Forces and Motion Click on the topic to go to that section Motion - - PDF document

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8th Grade

Forces

2015-10-27 www.njctl.org

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Forces and Motion

· Motion

Click on the topic to go to that section

· Graphs of Motion · Newton's Laws of Motion · Newton's 3rd Law & Momentum · Forces

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Motion

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• f Contents

Slide 4 / 159 What does it mean to be in motion?

With a partner, come up with a scientific explanation of what it means if an object is in

• motion. Don't just say an
• bject is moving!

Slide 5 / 159 What does it mean to be in motion?

An object is in motion if it changes position in relation to a certain place, called a reference point. Reference points are places or objects used to determine the motion of an

• bject.

It is extremely important to choose reference points carefully.

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Relative Motion

Motion is relative as it is dependent upon the reference point. Are you in motion right now? Think about it... Are you in motion compared to your desk? Are you in motion compared to the sun?

Slide 7 / 159 Measuring Motion

Speed is one of the many ways we measure motion. Speed is a measure of the distance traveled per unit of time. That means you can find the speed of any object that is in motion!

Slide 8 / 159 Finding Speed

Speed = Distance ⁄ Time

and

We can rearrange the letters in the speed equation and solve for any of the other 2 pieces of information.

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Finding Speed

Discussion time! · What are some possible units to measure speed? Remember that speed= distance/time! · How do you think speed is measured when driving in a car? · How would you measure speed of an engine? For reference, an animation of an internal combustion engine is shown below.

Slide 10 / 159 Units for Speed

The SI unit for distance is meters (m) and for time is seconds (s). Given these units, what will be the SI unit for speed? (Hint: recall the speed equation speed= distance/time)

Slide 11 / 159 Units for Speed

The SI unit for distance is meters (m) and for time is seconds (s). Given these units, what will be the SI unit for speed? (Hint: recall the speed equation speed= distance/time)

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Answer meters/second which is usually shortened to m/s

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1 A snail travels a distance of 10 m in 6000

• seconds. What is the snail's average speed?

A 60000 m/s B 0.02 m/s C 600 m/s D 0.002 m/s

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1 A snail travels a distance of 10 m in 6000

• seconds. What is the snail's average speed?

A 60000 m/s B 0.02 m/s C 600 m/s D 0.002 m/s

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Answer

D

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2 A blimp travels at 3 m/s for 1500 s. What distance does the blimp cover in that time? A 500 m/s B 4500 m/s C 4500 m D 500 m

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2 A blimp travels at 3 m/s for 1500 s. What distance does the blimp cover in that time? A 500 m/s B 4500 m/s C 4500 m D 500 m

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Answer

C

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Manipulate the speed of each car, solve for time, and predict which car will win!

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When we talk about speed, it is important to know that there is a difference between instantaneous speed and average speed. Average speed can be calculated by dividing the total distance by the total time. This is what is usually calculated by runners in a race. Instantaneous speed is the speed of an object at any moment in time (an instant of time). Can you think of an example where you would use instantaneous time?

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It might take 3 hours to travel 300 km in a car. What would the average speed of the car be? Calculate it now. Does that mean the car was going that speed for the whole 3 hours

• f the trip?

When you go on a trip in the car, do you go the same speed the whole time? Talk to a partner about this.

Average vs Instantaneous Speed Slide 16 / 159 Average vs Instantaneous Speed

Have you ever run a mile? Do you think you ran at the exact same speed the entire mile? Think about what runners do at the very end of a race.

Slide 17 / 159 Average vs Instantaneous Speed

When you ride on the bus to school, does the bus driver travel at the same speed the entire trip? School buses and other vehicles have speedometers that measure the speed of the vehicle at a specific moment in time. Do speedometers measure average speed or instantaneous speed?

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3 Your teacher times your mile run at 7.5 minutes, that means your speed was 0.13 mile/min. Was this your average speed or your instantaneous speed? AAverage Speed BInstantaneous Speed

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3 Your teacher times your mile run at 7.5 minutes, that means your speed was 0.13 mile/min. Was this your average speed or your instantaneous speed? AAverage Speed BInstantaneous Speed

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Answer

avg speed = 1 mile/ 7.5 min = 0.13 mile/min

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4 A student has built a model car that is designed to run at a constant speed. What should the student measure to test whether the car runs at a constant speed, average or instantaneous speed? AAverage Speed BInstantaneous Speed

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4 A student has built a model car that is designed to run at a constant speed. What should the student measure to test whether the car runs at a constant speed, average or instantaneous speed? AAverage Speed BInstantaneous Speed

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Answer

instantaneous speed

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5 A swordfish travels for two hours. The first hour he covers 110 kilometers, and the second hour he covers 84 kilometers. What is the average speed of the swordfish? A 110 km/h B 84 km/h C 97 km/h D 194 km/h Hint: Remember that Average speed is total distance travelled divided by total time

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5 A swordfish travels for two hours. The first hour he covers 110 kilometers, and the second hour he covers 84 kilometers. What is the average speed of the swordfish? A 110 km/h B 84 km/h C 97 km/h D 194 km/h Hint: Remember that Average speed is total distance travelled divided by total time

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Answer

C

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6 A dog walks outside to go the bathroom every day. On a given day, she walks 75 meters before she finds a spot to use the bathroom. She walks at an average speed of 2.5 meters per second. How long does it take her to find a place to use the bathroom? A 30 seconds B 2 minutes C 188 seconds D 90 seconds

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6 A dog walks outside to go the bathroom every day. On a given day, she walks 75 meters before she finds a spot to use the bathroom. She walks at an average speed of 2.5 meters per second. How long does it take her to find a place to use the bathroom? A 30 seconds B 2 minutes C 188 seconds D 90 seconds

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Answer

A

Slide 22 (Answer) / 159 Velocity

Velocity is another way to measure motion. Simply put, velocity is the speed of an object with a direction included. Runner's speed: 10 km/hr Runner's velocity: 10 km/hr to the East What do you notice about the units for speed and velocity?

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Why is velocity important?

Have you ever been in an airplane? Would would be the consequence of a pilot only knowing the speed of other nearby planes? Tornadoes travel at about 170 km/h. Why is knowing the velocity of a tornado important?

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7 Carlos and Gina are riding on their horses to go into town. They travel 70 meters in 7 seconds going west. What is their velocity? A 490 m/s west B 10 m/s west C 490 m/s D 10 m/s

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7 Carlos and Gina are riding on their horses to go into town. They travel 70 meters in 7 seconds going west. What is their velocity? A 490 m/s west B 10 m/s west C 490 m/s D 10 m/s

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Answer

B

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8 A car travels 100 km/h west for 2 hours. The car then travels 50 km/h east for one hour. What is the car's final position relative to its starting position? A 50 km west B 150 km west C 250 km west D 50 km east Hint: Find the distance and direction traveled for each leg of the trip first. Draw these distances on a number line using 0km as the starting point.

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8 A car travels 100 km/h west for 2 hours. The car then travels 50 km/h east for one hour. What is the car's final position relative to its starting position? A 50 km west B 150 km west C 250 km west D 50 km east Hint: Find the distance and direction traveled for each leg of the trip first. Draw these distances on a number line using 0km as the starting point.

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Answer

B

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Graphing Motion

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Graphing Motion

Graphs can be used to show motion and can be used to determine relationships! When graphing data, position should be on the y-axis and time on the x-axis. Drag and drop the variables onto the correct axis on the graph below. Position Time

Slide 28 / 159 Graphing Motion

Graphs can be used to show motion and can be used to determine relationships! When graphing data, position should be on the y-axis and time on the x-axis. Drag and drop the variables onto the correct axis on the graph below. Position Time

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Answer Position Time

Slide 28 (Answer) / 159 Graphing Motion

Use the graph below to calculate speed at 1, 2, and 3 seconds. Do you notice a pattern?

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Graphing Motion

2 m/ 1s = 2 m/s 4 m/ 2s = 2 m/s 6 m/ 3s = 2 m/s The speed is 2 m/s at each of the three seconds! In other words, the speed is constant.

Slide 30 / 159 Graphing Motion

When interpreting a graph, it is important to look for relationships between variables. These relationships can be strong, weak, or not present at all. The graph below shows a strong relationship between position and

• time. Can you describe what this relationship is?

Slide 31 / 159 Graphing Motion

When interpreting a graph, it is important to look for relationships between variables. These relationships can be strong, weak, or not present at all. The graph below shows a strong relationship between position and

• time. Can you describe what this relationship is?

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Answer As the time increases at a constant rate, so does the position.

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Graphing Motion

A weak relationship is when significant changes in one variable cause minimal changes in the other variable. Is there any pattern in the graph below? Circle the patterns.

Slide 32 / 159 Graphing Motion

When there is no relationship between the variables, there will not be a pattern present. Is there any pattern in the graph below?

Slide 33 / 159 The Importance of Slope

Position versus time graphs can be used to find speed and compare speeds.When we talk about the slope of a line, we are talking about how steep a line is. Look at the skier to the right. He is on a very difficult trail. Would an easier trail be steeper or more flat? How would the slopes of these two trails compare?

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The Importance of Slope

In a position versus time graph, the y-axis is the position and the x-axis is the time. Recall that the relationship between position and time is speed. So when we are looking at the slope, we are looking at the speed . The steeper the slope of the line on a position versus time graph, the greater the speed! The slope of the black line gives us the speed of the bicycler.

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Which walker has a greater speed? How can you tell in terms of the slopes of the graphs? 9 A B

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Which walker has a greater speed? How can you tell in terms of the slopes of the graphs? 9 A B

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Answer

Walker #2 because the slope is steeper. This walker covered the same distance in less time than walker #1.

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Relate the shape of the graph (slopes!) to the man's motion.

Graphing Motion Simulation Lab

Click on the image to the left to launch the simulation. You will need to download it to be able to use it. Click on the CHARTS tab at the top. Minimize the velocity graph and the acceleration graph by clicking on the RED dash on each graph. KEEP POSITION! CLICK PLAY Drag the man to the RIGHT at a constant speed, STOP, and finally drag the man at a constant speed Left back to the starting point (zero).

Slide 37 / 159 Acceleration

Constant speed is when an object's speed does not change; however, most objects do not travel at a constant speed. Acceleration is a way to measure changing motion. Do you walk at the exact same speed from class to class? What if you are late for class? Are you ever accelerating when you go to class? Can you define acceleration?

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speed speed change in direction

Acceleration

Acceleration occurs when there is a change in velocity. Remember, velocity is speed with direction. So acceleration occurs any time there is an increase in speed, a decrease in speed, or a change in direction.

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Acceleration

Acceleration is a measure of the change in velocity per unit of time. Here is the equation for acceleration.

vf -vo

t

a =

acceleration = (final velocity-initial velocity) time

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10 A school bus driver sees an old man crossing the street at an intersection. The bus driver hits the brake pedal and turns the steering wheel to avoid

• him. Describe the acceleration of the bus.

A It increased speed B It decreased speed C It changed direction

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10 A school bus driver sees an old man crossing the street at an intersection. The bus driver hits the brake pedal and turns the steering wheel to avoid

• him. Describe the acceleration of the bus.

A It increased speed B It decreased speed C It changed direction

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Answer

B & C

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11 A dragster launches from rest to 50 mi/hr at the start of a race. How did the car accelerate? A increased speed B decreased speed C changed direction

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11 A dragster launches from rest to 50 mi/hr at the start of a race. How did the car accelerate? A increased speed B decreased speed C changed direction

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Answer

A

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The school bus picks you up at the bus stop and takes 60 seconds to accelerate to 120 km/h. What is the acceleration of the school bus?

vf -vo

t

a = Practice Solving for Acceleration Slide 43 / 159

The school bus picks you up at the bus stop and takes 60 seconds to accelerate to 120 km/h. What is the acceleration of the school bus?

vf -vo

t

a = Practice Solving for Acceleration

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Answer

a = (120 km/h - 0 km/h) 60 s a = 2 km/h per second

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12 A plane's speed increases from 25 m/s to 60 m/s in 5

• seconds. What is the acceleration of the plane?

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12 A plane's speed increases from 25 m/s to 60 m/s in 5

• seconds. What is the acceleration of the plane?

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Answer

a = (60 m/s - 25 m/s) 5 s a = 7 m/s/s OR 7m/s2

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13 After traveling for 10 seconds, a runner reaches a speed of 12m/s. If the runner started from rest, what is the runner's acceleration?

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13 After traveling for 10 seconds, a runner reaches a speed of 12m/s. If the runner started from rest, what is the runner's acceleration?

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Answer

a = (12 m/s - 0 m/s) 10 s a = 1.2m/s2

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14 A parachute opens and slows a skydiver from 65m/s to 45m/s in a period of 5 seconds. What is the acceleration of the skydiver?

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14 A parachute opens and slows a skydiver from 65m/s to 45m/s in a period of 5 seconds. What is the acceleration of the skydiver?

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Answer

a = (45m/s - 65m/s) 5 s a = -4m/s2 or decelerated 4m/s2

Slide 46 (Answer) / 159 Acceleration and Graphs

If the speed and direction of an object are constant, then the acceleration is zero. Look at the car's speed at 20s, 60s, and 100s. Is the car accelerating?

Slide 47 / 159 Acceleration and Graphs

If the speed and direction of an object are constant, then the acceleration is zero. Look at the car's speed at 20s, 60s, and 100s. Is the car accelerating?

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Answer Only if the car is changing

• directions. Based on speed alone,

the car does not accelerate.

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Acceleration and Graphs

Acceleration is positive when speed is increasing. Negative acceleration (deceleration) is when speed is decreasing. How could you describe the slopes of each of these lines?

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15 A driver hits the brakes to slow down at an

• intersection. As the car's speed is decreasing it has:

A positive acceleration B negative acceleration C no acceleration D more information is needed

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15 A driver hits the brakes to slow down at an

• intersection. As the car's speed is decreasing it has:

A positive acceleration B negative acceleration C no acceleration D more information is needed

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Answer

B

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16 Which of the following graphs shows a positive acceleration? A B C x Y

Speed (m/s) Time (s)

x

Y

Speed (m/s) Time (s)

x Y

Speed (m/s) Time (s)

D x

Y

Speed (m/s) Time (s)

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16 Which of the following graphs shows a positive acceleration? A B C x Y

Speed (m/s) Time (s)

x

Y

Speed (m/s) Time (s)

x Y

Speed (m/s) Time (s)

D x

Y

Speed (m/s) Time (s)

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Answer

C

Slide 50 (Answer) / 159 Constant Speed Graphical Analysis Lab

We will us a constant velocity vehicle to collect data and graph our results. The graph will help us determine the average speed.

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Acceleration and Graphs

The slope of a position versus time graph can also show acceleration. If the slope curves and gets steeper, then positive acceleration is occurring. If the slope curves and becomes less steep, then negative acceleration is occurring.

Slide 52 / 159 Distance vs. Time Graphs of Accelerating Objects

Click on the image to download the simulation. Click on the CHARTS tab. Type in 1 m/s

2 into the acceleration

value and hit play. Sketch the shape of the distance vs. time graph: Sketch the shape of the velocity vs. time graph:

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17 Which of the following speed vs time graphs (on the left) correspond to the position vs time graph on the right? A B C

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17 Which of the following speed vs time graphs (on the left) correspond to the position vs time graph on the right? A B C

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Answer

A

Slide 54 (Answer) / 159 Accelerated Motion on an Inclined Plane Lab

In this lab you will record the time it takes for a car to go different distances down an inclined plane. The data will be graphed and then you will analyze the results.

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Forces

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What Are Forces?

Forces are ________ or ______ in a given direction. Forces affect how objects move.

Slide 57 / 159 Forces Affect Motion

At your table, make a list of ways forces can affect objects. There are many ways. Write a few of these ways below.

Slide 58 / 159 Forces Acceleration

cause

The Big Idea...

Since forces can cause changes in the speed or direction of an

• bject, we can say that forces cause changes in velocity, so

forces cause acceleration!

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Units of Force

Forces are measured in newtons (N). You probably measure yourself on a scale in pounds. One pound is equal to 4.448 newtons. Just like velocity, force has direction. When forces are demonstrated both magnitude and direction should be shown.

10 N

What is the magnitude of the force shown above? How about the direction?

Slide 60 / 159 Balanced Forces

If you and a friend both push with the same strength on each side of a table, will it move? Two or more opposite forces acting on an object are considered balanced if their effects cancel each other out. Balanced forces do not cause a change in an object's motion.

8 N 8 N

The box to the right is at rest and will remain at rest since the

• pposite forces acting
• n it are balanced.

Slide 61 / 159 Unbalanced Forces

If the effects of the forces don't cancel each other out (one force is stronger than others), the forces are unbalanced forces. Unbalanced forces do cause a change in motion; speed and/or direction. Think about Tug-Of-War. How does one side win?

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Unbalanced Forces

15 N 8 N

Two ways to interpret this diagram are to say: there is a 15N force to the right and an 8N force to the left OR we can say there is a +15N force and a -8N force. What does the negative on the -8N tell us?

Slide 63 / 159 Unbalanced Forces

15 N 8 N

The box was initially at rest. Since the forces acting on the box are unbalanced, the box will start moving. Does the box accelerate? Which way do you think the box will move and why?

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18 Forces are all around us. Which of the following do you think are examples of forces? (choose all that apply) A Gravity B Friction C Muscles D Wind

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18 Forces are all around us. Which of the following do you think are examples of forces? (choose all that apply) A Gravity B Friction C Muscles D Wind

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Answer

A & B

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19 What is the SI unit for force? A Pounds B Kilograms C Newtons

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19 What is the SI unit for force? A Pounds B Kilograms C Newtons

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Answer

C

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20 A +10 N force acts on a car and at the same time, a -20 N force acts on the car. What is the net force acting on the car and is it balanced? A -30 N unbalanced B

• 10 N unbalanced

C

• 10 N balanced

D + 30 balanced Hint: Net force is the total (or sum) of all the forces acting on an object.

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20 A +10 N force acts on a car and at the same time, a -20 N force acts on the car. What is the net force acting on the car and is it balanced? A -30 N unbalanced B

• 10 N unbalanced

C

• 10 N balanced

D + 30 balanced Hint: Net force is the total (or sum) of all the forces acting on an object.

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Answer

B

Slide 67 (Answer) / 159 Friction

Forces are present all around us, but can not usually be seen. Friction is a force that resists motion and we experience daily. When you run, walk, sit on the couch, brush your hair, and write you experience friction. You are experiencing friction right now!

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Friction

The force of friction is caused by microscopic particles touching each

• ther. These microscopic pieces on both surfaces cause friction.

Friction is affected by how hard the surfaces push together and the types of surfaces involved.

Click here to see the force of friction clip

There are many types of friction.

Slide 69 / 159 Static Friction

Static friction acts on objects that are not moving. Have you ever wondered why it is so hard to start moving a heavy object like a dresser or couch, but then once it starts moving it is easier? That is because you have to overcome the force of static friction! Static friction holds the couch in place and keeps it from moving.

Slide 70 / 159 Sliding Friction

Sliding friction occurs when objects slide over each other. Sliding friction is easier to overcome than static friction. That is why the couch is easier to move once it starts sliding!

Click here to see sliding friction in action.

Sliding friction is also known as kinetic friction.

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Fluid Friction

Fluid friction occurs when objects move through a fluid. Remember, air is a fluid, so you continuously experience fluid friction!

Click here to see the effects of fluid friction.

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Rolling friction exists when objects roll across surfaces. With a partner, make a list of other examples

• f rolling friction. Hint:

There are many examples in sports.

Slide 73 / 159 Friction

The force of friction is measured in Newtons like all other forces. When you are trying to determine where to put the friction force, just remember that friction acts opposite to motion!

stationary box force applied by person pushing box static friction force

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21 Friction acts more on objects in motion than it does on objects at rest. True False

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21 Friction acts more on objects in motion than it does on objects at rest. True False

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Answer

False

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22 Friction always opposes the motion of an

• bject.

True False

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22 Friction always opposes the motion of an

• bject.

True False

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Answer

TRUE

Slide 76 (Answer) / 159 Gravity

Forces are present all around us and always act in pairs, so we usually experience more than one force. Gravity is a force that pulls objects towards each other. How does gravity act on objects here on Earth? Use the picture to the right to help you with your answer.

Slide 77 / 159 Law of Gravitation

The Law of Universal Gravitation tells us that gravity acts between all objects in the universe. This means that without exception, any two objects in the universe attract each other!

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Factors Affecting Gravity

Gravity is affected by both mass and distance. The greater the distance between two objects, the less the gravitational force between them. The greater the mass of the object, the greater the object's gravitational force. You have learned about mass in the past. Can you define mass? Which of these examples has more gravity? Why?

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23 The force of gravitation between an object and a planet is increased as they move away from each other. True False

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23 The force of gravitation between an object and a planet is increased as they move away from each other. True False

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Answer

False

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24 The force of gravitation between an object and a planet is decreased if the object increases mass. True False

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24 The force of gravitation between an object and a planet is decreased if the object increases mass. True False

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Answer

False

Slide 81 (Answer) / 159 Mass and Weight

What is weight? You have also learned the difference between mass and weight in the

• past. What can you recall about mass and weight?

Think about astronauts on the International Space Station. What do you know about their masses and weights?

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Wait, so mass affects gravity?

Weight is a measure of the gravitational force exerted on an object. Weight varies depending on gravitational force, but mass does not. Weight = mass x gravity Our moon has a gravity that is

• ne sixth of that on Earth.

What would that do to your weight on the moon? Would your mass change on the moon?

Slide 83 / 159 What is "g"?

"g" is the acceleration due to gravity. On Earth, our "g" is approximately 9.8 m/s2 . On other planets, acceleration due to gravity will vary depending

• n the mass of the planet. In general, the more massive the
• bject, the larger the value of g!

Jupiter g = 26.1 m/s2 Earth's Moon g = 1.67 m/s2

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25 A 50 kg kid is on planet Earth, where g = 9.8 m/s2. What is the boy's weight? A 5.1 m/s B 490 N C 490 kg D 5.1 N

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25 A 50 kg kid is on planet Earth, where g = 9.8 m/s2. What is the boy's weight? A 5.1 m/s B 490 N C 490 kg D 5.1 N

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Answer

B

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26 A 50 kg kid is on planet Earth, where g = 9.8 m/s2. What is the boy's mass? A 50 kg B 490 N C 490 kg D 5.1 N

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26 A 50 kg kid is on planet Earth, where g = 9.8 m/s2. What is the boy's mass? A 50 kg B 490 N C 490 kg D 5.1 N

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Answer

A

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27 A 50 kg kid is on the moon, where g = 1.67 m/s2. What is the boy's weight? A 83.5 kg B 29.9 kg C 83.5 N D 29.9 N

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27 A 50 kg kid is on the moon, where g = 1.67 m/s2. What is the boy's weight? A 83.5 kg B 29.9 kg C 83.5 N D 29.9 N

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Answer

C

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28 A 50 kg kid is on the moon, where g = 1.67 m/s2. What is the boy's mass? A 83.5 kg B 50 kg C 83.5 N D 50 N

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28 A 50 kg kid is on the moon, where g = 1.67 m/s2. What is the boy's mass? A 83.5 kg B 50 kg C 83.5 N D 50 N

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Answer

B

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29 The larger the planet, the larger the __________.

A mass B weight C gravity D all could be correct

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29 The larger the planet, the larger the __________.

A mass B weight C gravity D all could be correct

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Answer

D

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Gravity and Motion

Galileo showed that falling objects accelerate equally no matter what their mass is. This is strictly true when gravity is the only force acting on a falling object and is known as free fall. When an object is in free fall, it accelerates at 9.8 m/s2 10kg If these two stones are dropped from the same height at the same time, which hits the ground first? 1kg

Click here to see a bowling ball and golf ball being dropped

Slide 90 / 159 Gravity and Motion

Galileo showed that falling objects accelerate equally no matter what their mass is. This is strictly true when gravity is the only force acting on a falling object and is known as free fall. When an object is in free fall, it accelerates at 9.8 m/s2 10kg If these two stones are dropped from the same height at the same time, which hits the ground first? 1kg

Click here to see a bowling ball and golf ball being dropped

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Answer If these falling rocks only had gravity acting on them (in free fall), they would both fall at the same rate of 9.8 m/s2 . They would both hit the ground at the same time!

Slide 90 (Answer) / 159 Gravity and Motion

The following video shows a feather and a ball bearing being dropped from a small height. Which simulation showed the objects in free fall? Critical thinking: What was happening in the simulation that did not illustrate free fall?

Click here to see a feather and a ball bearing being dropped.

Slide 91 / 159

Gravity and Motion

The following video shows a feather and a ball bearing being dropped from a small height. Which simulation showed the objects in free fall? Critical thinking: What was happening in the simulation that did not illustrate free fall?

Click here to see a feather and a ball bearing being dropped.

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Answer In the first simulation, the objects fell at different rates. In the second simulation, the objects fell at the same rate. The second simulation illustrates free fall. Critical thinking: Move on to the next slide to learn the answer to this question!

Slide 91 (Answer) / 159 Air Resistance

Try this: Crumple up two pieces of paper individually and drop them both from the same height at the same time. Which hits the ground first? Now drop a crumpled piece of a paper and a non-crumpled piece of paper in the same way. What's the difference? Objects are not always truly in free fall because they experience air resistance. Air resistance is a fluid friction experienced by falling objects. When objects experience air resistance, they don't fall at a rate of 9.8 m/s2.

Click here to see a feather and a hammer being dropped

• n the moon. What happens

with no air resistance?

Slide 92 / 159 Air Resistance

The flat piece of paper fell at a slower rate because it had more surface area. This greater surface area resulted in the paper experiencing air resistance. For the crumpled paper, air resistance was probably very tiny and thus could be ignored. The crumpled paper was essentially in free fall. People use parachutes when they jump out of planes. Why?

Slide 93 / 159

Net Force

As you know, many forces are acting on us and other objects. To determine the total force acting on an object, the forces are added and subtracted as appropriate to find the net force. When several forces are acting on the same object, the net force might be zero...

5 N

• 5 N

Net Force = 0

If the net force on an object is zero, then it is in equilibrium. When an object is at rest, the net force is zero.

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If the net force is not equal to zero, then there is a change in the motion

• f the object. The object is not in equilibrium. What is the net force in the

example below?

5 N

• 12 N

Net Force = Unbalanced Forces

What direction is this box going to move?

Slide 95 / 159

5 N

• 12 N

Net Force = -7 N

In this case, the object will accelerate towards the left because the NET FORCE is toward the left.

Unbalanced Forces

On Earth, gravity and friction are two of the unbalanced forces that frequently change an object's motion.

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30 What is the net force acting on the object below? Is the object in equilibrium? 7 N

• 8 N
• 10 N

Slide 97 / 159

30 What is the net force acting on the object below? Is the object in equilibrium? 7 N

• 8 N
• 10 N

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Answer

• 11 N

Slide 97 (Answer) / 159

31 What is the net force acting on the object below? Is the object in equilibrium? 25 N

• 15N
• 10 N

Slide 98 / 159

31 What is the net force acting on the object below? Is the object in equilibrium? 25 N

• 15N
• 10 N

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Answer

0 N

Slide 98 (Answer) / 159

32 Acceleration due to gravity on Jupiter is 26.1 m/s2. How much would a 60 kg person weigh on Jupiter?

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32 Acceleration due to gravity on Jupiter is 26.1 m/s2. How much would a 60 kg person weigh on Jupiter?

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Answer

1566 N

Slide 99 (Answer) / 159

33 Acceleration due to gravity on Earth's Moon is 1.67 m/s2. How much would a 60 kg person weigh

• n Earth's Moon?

Slide 100 / 159

33 Acceleration due to gravity on Earth's Moon is 1.67 m/s2. How much would a 60 kg person weigh

• n Earth's Moon?

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Answer

100.2 N

Slide 100 (Answer) / 159 Sticky Sneakers Lab

How does the amount of friction between a shoe and a surface compare for different shoes? Which shoes would be best for playing basketball? Which would be best for bowling? These questions will be answered in this lab.

Slide 101 / 159

Newton's Laws of Motion

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• f Contents

Slide 102 / 159 The History of the Laws of Motion

Aristotle, a Greek philosopher, and Galileo Galilei, an Italian astronomer, may have been two of the first scientists to try to explain gravity and motion.

Slide 103 / 159

In the late 1600s, Sir Isaac Newton used Galileo's ideas to create three basic laws of motion.

The History of the Laws of Motion

Sir Isaac Newton contributed to advances in physics, mathematics, and astronomy.

Slide 104 / 159

Laws of Motion

Newton may be one of the greatest scientists in

• history. The three laws of

motion he created are three of the most used natural laws in science. These laws help us to make sense of the world around us.

Slide 105 / 159

Newton was inspired by the apple falling from the tree and asked himself if gravity might also be the force holding the moon in orbit. Newton found that gravity plays a role in other orbital motions as well!

Laws of Motion Slide 106 / 159 Newton's First Law of Motion

The first law of motion tells us that an object at rest stays at rest, and an object moving at a constant velocity will continue moving at a constant velocity, unless acted on by an unbalanced force. On Earth, gravity and friction are two of the unbalanced forces that frequently change an

• bject's motion.

Slide 107 / 159

The first law of motion is sometimes referred to as the law of inertia.

Newton's First Law of Motion

Inertia is the tendency of an object to resist a change in motion.

Slide 108 / 159 The First Law of Motion

The first law basically tells us that motion will not change without a net force. So, if an object stops moving or starts moving, you know there is a net force. If there is a net force, then the forces are

• unbalanced. As you know, unbalanced

forces cause changes in motion! Apply Newton's First Law of Motion to the baseball player sliding into second

• base. What are some forces acting on

him?

Slide 109 / 159 Inertia Simulation

Click on the image to the left to launch simulation. Click on the motion tab, check speed to add speedometer, and place a person on the skateboard. Apply a force to the object and look at the speedometer. What happened? Stop applying the force. What happens?

Slide 110 / 159

Application of The First Law of Motion

Have you ever wished that you could just tell your clothing to move itself to the closet? Unfortunately, we know that objects don't move on their own. An unbalanced force is required to make an object change its state

• f motion.

Slide 111 / 159

Imagine you need to move a few pieces of furniture in your

• room. Would you rather move your dresser with everything in

it or your dresser when its empty?

Application of The First Law of Motion

Be sure to use the term inertia in your answer. Based on your answer, how are inertia and mass of an

• bject related?

Slide 112 / 159

34 Inertia is the resistance of an object to change in its state of motion. True False

Slide 113 / 159

34 Inertia is the resistance of an object to change in its state of motion. True False

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Answer

True

Slide 113 (Answer) / 159

35 The law of inertia applies to___________. A moving objects B nonmoving objects C both moving and nonmoving objects

Slide 114 / 159

35 The law of inertia applies to___________. A moving objects B nonmoving objects C both moving and nonmoving objects

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Answer

C

Slide 114 (Answer) / 159

Which has more Inertia?

A Tennis Ball or a Bowling Ball? Why?

Slide 115 / 159

36 Which object has the greatest inertia? A Car B Tennis Ball C Moving Freight Train

Slide 116 / 159

36 Which object has the greatest inertia? A Car B Tennis Ball C Moving Freight Train

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Answer

C

Slide 116 (Answer) / 159

37 Which object has the greatest inertia? A Car B Tennis Ball C Freight Train at rest

Slide 117 / 159

37 Which object has the greatest inertia? A Car B Tennis Ball C Freight Train at rest

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Answer

C

Slide 117 (Answer) / 159

38 Which object has the greatest inertia? A Moving Tennis Ball B Tennis Ball at Rest C Both have the same Inertia

Slide 118 / 159

38 Which object has the greatest inertia? A Moving Tennis Ball B Tennis Ball at Rest C Both have the same Inertia

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Answer

C

Slide 118 (Answer) / 159

39 A ball will accelerate when it is acted on by 2 equal forces pointing in opposite directions. True False

Slide 119 / 159

39 A ball will accelerate when it is acted on by 2 equal forces pointing in opposite directions. True False

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Answer

FALSE

Slide 119 (Answer) / 159

Newton's Second Law

Newton's second law states that acceleration depends on both force and mass. It supports the idea that unbalanced forces cause acceleration. Remember, acceleration is an increase in speed, a decrease in speed,

• r a change in direction.

Slide 120 / 159 Newton's Second Law

Unbalanced forces cause acceleration. There is a direct relationship between force and acceleration. Mass and acceleration are inversely proportional. Forces that cause a net force on an

• bject are

unbalanced. As force increases, acceleration increases. As mass increases, acceleration decreases.

Slide 121 / 159 Newton's Second Law

Unbalanced forces cause acceleration, so unbalanced forces cause an increase in speed, a decrease in speed, and/or a change in direction. The second law relates force, mass, and acceleration. Force = mass x acceleration

Slide 122 / 159

We can rearrange this to solve for the other variables. You do not need to know how to rearrange it, but you do have to be able to select the right formula for solving your problem.

F = ma a = F m m = F a Newton's Second Law Slide 123 / 159 Application of Newton's Second Law

The second law states that if force is increased, acceleration will also increase. If you want to shoot a very fast penalty kick into the soccer net, how do you kick it?

Slide 124 / 159 Application of Newton's Second Law

The second law also tells us that the greater the mass, the less the acceleration (if the force is constant). How hard is it to pull one person in the wagon? What happens when you add another person to the wagon? Have you ever pulled your friends in a wagon?

Slide 125 / 159

40 When the force acting on an object increases, the resulting acceleration will: A remain constant B increase C decrease

Slide 126 / 159

40 When the force acting on an object increases, the resulting acceleration will: A remain constant B increase C decrease

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Answer

B

Slide 126 (Answer) / 159

41 When an object's mass increases but the applied force stays the same, the resulting acceleration will: A remain constant B increase C decrease

Slide 127 / 159

41 When an object's mass increases but the applied force stays the same, the resulting acceleration will: A remain constant B increase C decrease

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Answer

C

Slide 127 (Answer) / 159

42 You are riding your bicycle to the park to meet a few friends. As you ride, you apply a force of 30 N and accelerate at a rate of 0.4 m/s2. What is the total mass of the bicycle and you? A 75 kg B 12 kg C 120 kg

Slide 128 / 159

42 You are riding your bicycle to the park to meet a few friends. As you ride, you apply a force of 30 N and accelerate at a rate of 0.4 m/s2. What is the total mass of the bicycle and you? A 75 kg B 12 kg C 120 kg

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Answer

A

Slide 128 (Answer) / 159

43 You are pushing a shopping cart so that it accelerates at 0.2 m/s2. You start filling the shopping cart with food. Do you need to change how you push on the cart for it to maintain the same acceleration? If so, in what way? A No B Yes, push harder C Yes, push softer

Slide 129 / 159

43 You are pushing a shopping cart so that it accelerates at 0.2 m/s2. You start filling the shopping cart with food. Do you need to change how you push on the cart for it to maintain the same acceleration? If so, in what way? A No B Yes, push harder C Yes, push softer

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Answer

B

Slide 129 (Answer) / 159 Newton's 2nd Law Simulation

Click on the image to the left to download the Simulation. Click the Acceleration Lab Tab Check show Forces, masses, acceleration, and turn friction to none. Place 1 crate onto the surface and apply a 500 N force, note the acceleration. Stack 2 crates onto the surface and apply a 500 N force,note the acceleration. What was the effect of adding mass to the simulation on the resulting acceleration produced?

Slide 130 / 159

Newton's 3rd Law of Motion & Momentum

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• f Contents

Slide 131 / 159 Newton's Third Law of Motion

Newton's third law of motion, unlike the first and second, pertains to forces between two

• bjects.

When you kick a soccer ball, do you feel the force of the ball against your foot? Does the ball "feel" the force

• f your foot?

Newton's third law explains this occurrence.

Slide 132 / 159

Have you ever jumped off a skateboard? What happens to the board when you jump off? Draw an arrow below to show what direction the board will go.

Newton's Third Law of Motion

This is Newton's third law of motion at work! You applied a force to the board and the board applied an equal (in magnitude) and

• pposite (in direction) force on you.

We call these Action-Reaction Forces.

Slide 133 / 159

44 When you sit on a chair, the seat of the chair pushes up on you with more force than your weight. True False

Slide 134 / 159

44 When you sit on a chair, the seat of the chair pushes up on you with more force than your weight. True False

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Answer

False

Slide 134 (Answer) / 159

45 Action-Reaction forces are always found in pairs that are equal and opposite. True False

Slide 135 / 159

45 Action-Reaction forces are always found in pairs that are equal and opposite. True False

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Answer

True

Slide 135 (Answer) / 159 Newton's Third Law of Motion

Forces always exist in pairs! Newton's third law defines these action and reaction forces.

Click here to see how Newton's Third Law applies to the physics of a rocket.

Slide 136 / 159

As you kick the soccer ball, you apply an action force to the ball, and the ball applies a reaction force on your foot. These forces are equal in strength and opposite in direction. Why does the ball accelerate more quickly than you and your foot?

Newton's Third Law of Motion Slide 137 / 159

As you kick the soccer ball, you apply an action force to the ball, and the ball applies a reaction force on your foot. These forces are equal in strength and opposite in direction. Why does the ball accelerate more quickly than you and your foot?

Newton's Third Law of Motion

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Answer Because the ball has less mass! Remember Newton's 1st and 2nd law!

Slide 137 (Answer) / 159 Newton's Third Law of Motion

The third law states that for every action force, there is an equal, but opposite reaction force.

a c t i

• n

r e a c t i

• n

This means that if one object applies a force to another object, then the

• ther object exerts an equal and opposite force on the first object.

Slide 138 / 159

46 When you jump off a skateboard, which of the following is true? A You accelerate more than the skateboard. B You and the skateboard accelerate equal but

• pposite amounts.

C The skateboard accelerates more than you.

Slide 139 / 159

46 When you jump off a skateboard, which of the following is true? A You accelerate more than the skateboard. B You and the skateboard accelerate equal but

• pposite amounts.

C The skateboard accelerates more than you.

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Answer

C

Slide 139 (Answer) / 159 Newton's Third Law of Motion

According to Newton's 3rd law, the cart pulls on the man just as hard as the man pulls on the cart. Do these forces cancel each

• ther out preventing the cart and man from moving?

Slide 140 / 159 Newton's Third Law of Motion

According to Newton's 3rd law, the cart pulls on the man just as hard as the man pulls on the cart. Do these forces cancel each

• ther out preventing the cart and man from moving?

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Answer No, they are not acting on the same

• bject!! Each force is acting on a

different object.

Slide 140 (Answer) / 159

Newton's Third Law of Motion

Action: The man applies force to the cart that moves the cart forward. Reaction: The cart applies an equal and opposite force on the man. Each force in the pair acts on a different object!

Slide 141 / 159 The Truth about Action Reaction Forces

If a force occurs, there are action reaction forces! Action reaction forces: can cause changes in motion are equal in strength but

• pposite in

direction act on different

• bjects

Slide 142 / 159

47 Which of the following statements pertains to the third law of motion? A Action and reaction pairs always act on the same object. B Mass is indirectly proportional to acceleration. C An object at rest will remain at rest unless acted on by an unbalanced force. D If a force occurs, action reaction forces are present.

Slide 143 / 159

47 Which of the following statements pertains to the third law of motion? A Action and reaction pairs always act on the same object. B Mass is indirectly proportional to acceleration. C An object at rest will remain at rest unless acted on by an unbalanced force. D If a force occurs, action reaction forces are present.

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Answer

D

Slide 143 (Answer) / 159

48 A textbook is resting on a table. Tommy pushes the book rightwards. What is an action reaction pair in this scenario? A The book exerts a downward force on the

• table. The table exerts an upward on Tommy.

B Tommy exerts a rightward force on the book. The book exerts a downward force on the table. C The book exerts a leftward force on Tommy. Tommy exerts a rightward force on the book. D Tommy exerts a downward force on the table. The table exerts a rightward force on Tommy.

Slide 144 / 159

48 A textbook is resting on a table. Tommy pushes the book rightwards. What is an action reaction pair in this scenario? A The book exerts a downward force on the

• table. The table exerts an upward on Tommy.

B Tommy exerts a rightward force on the book. The book exerts a downward force on the table. C The book exerts a leftward force on Tommy. Tommy exerts a rightward force on the book. D Tommy exerts a downward force on the table. The table exerts a rightward force on Tommy.

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Answer

C

Slide 144 (Answer) / 159

49 Action reaction pairs cancel each other out since they are equal and opposite to each other. True False

Slide 145 / 159

49 Action reaction pairs cancel each other out since they are equal and opposite to each other. True False

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Answer

False

Slide 145 (Answer) / 159 Momentum

Newton's third law tells us that action reaction forces are equal and

• pposite, but that does not mean that the effects of those forces are

equal. After watching the video, discuss the following: · what was the action reaction pair? · did both carts accelerate the same? Why or why not? · how is this related to Newton's 1st and 2nd law of motion?

Click here to see how equal action reaction pairs cause different motions.

Slide 146 / 159

Momentum

Remember Newton's law of inertia. Objects with more mass (more inertia) have more reluctance to change their motion and vice versa. Also recall Newton's 2nd law. Objects with more mass accelerate less than objects with less mass under the same force (and vice versa). Both carts experience the same strength in force (Newton's 3rd law). But the cart on the right experiences a greater change in motion because it has less mass. Why?

Slide 147 / 159 Momentum

If we understand Newton's third law and momentum, we can predict how the motion of colliding objects will change. Momentum is the result of the mass of the object times the object's velocity. momentum (kg-m/s) = mass (kg) x velocity (m/s)

Slide 148 / 159 Momentum

Find the momentum of a skateboarder with a mass of 50 kg traveling at a velocity of 4 m/s west.

p = mv

Slide 149 / 159

Momentum

Find the momentum of a skateboarder with a mass of 50 kg traveling at a velocity of 4 m/s west.

p = mv

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Answer p = mv p = (50kg) (4 m/s) p = 200 kg m/s west If you know the direction of the velocity, you also know the direction of the momentum!

Slide 149 (Answer) / 159

50 How can a small insect have the same momentum as a large car? A insect has large speed B both car and insect are at rest C insect has no mass D A & B

Slide 150 / 159

50 How can a small insect have the same momentum as a large car? A insect has large speed B both car and insect are at rest C insect has no mass D A & B

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Answer

D

Slide 150 (Answer) / 159

51 If a 2 kg toy truck is moving at 4 m/s, what is the toy's momentum? A 3 m/s B 2 kg m/s C 8 kg m/s D 8 m/s

Slide 151 / 159

51 If a 2 kg toy truck is moving at 4 m/s, what is the toy's momentum? A 3 m/s B 2 kg m/s C 8 kg m/s D 8 m/s

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Answer

C

Slide 151 (Answer) / 159 Law of Conservation of Momentum

Momentum is conserved (remains the same) during an interaction as long as the objects are not affected by outside forces. This means that the total momentum of objects prior to hitting each other will equal the total momentum of the objects after the interaction. Any momentum lost by one object is gained by the other!

Slide 152 / 159

Momentum Simulation

Click on the image to the left to launch and play the simulation. Make each object the same mass by moving sliders (1 kg each works best). Click show values. Compare the total momentum of the balls added before and after the collision. What happens to the total amount of momentum before and after the collision?

Slide 153 / 159 Law of Conservation of Momentum

Fill in the missing values. Remember that the law of conservation tells us that the total momentum before a collision is equal to the total momentum after a collision. Car Mass

(kg) Velocity (m/s) Momentum (kg m/s) 1 1000 6 2 2000 Car Mass (kg) Velocity (m/s) Momentum (kg m/s) 1 1000

• 12

2 2000

Before Collision Data After Collision Data

Total Momentum: ___________ Total Momentum: ___________ HINT: p=mv can be rearranged to v=p/m and a negative momentum means the object moves left!

Slide 154 / 159

52 What two variables does momentum depend on? A mass and volume B mass and acceleration C mass and velocity D mass and force

Slide 155 / 159

52 What two variables does momentum depend on? A mass and volume B mass and acceleration C mass and velocity D mass and force

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Answer

C

Slide 155 (Answer) / 159

53 The total amount of momentum before and after a collision may vary. True False

Slide 156 / 159

53 The total amount of momentum before and after a collision may vary. True False

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Answer

FALSE

Slide 156 (Answer) / 159

Newton's Third Law and Momentum Lab

Click on the picture to go to the website for the lab.

Slide 157 / 159 Newton's Laws of Motion Lab

Rotate from station to station in the classroom. Follow the directions that correspond with your station. Make observations, record your results, and answer the questions for each station. Station 1: Inertia is Nuts! Station 2: Balloon Blow Out Station 3: Spinning Penny Station 4: Water Whirl Station 5: Dominoes Station 6: Yay for Seatbelts and Airbags Station 7: Free Fallin' Station 8: Rolling Chair

Slide 158 / 159 Images Cited

A7N8X 2012, 4-Stroke Engine, gif, viewed 29 June 2015, <https://commons.wikimedia.org/wiki/File:4-Stroke-Engine.gif>. Luke Ma 2012, Pull Carts Kyoto, Japan, jpg, viewed 7 July 2015, <https://commons.wikimedia.org/wiki/File:Pull_carts,_Kyoto,_Japan_(8587844087).jpg>

Slide 159 / 159