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www.njctl.org
8th Grade Forces and Motion Classwork & Homework
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Classwork #1: Motion and Speed
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1 Define motion.
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2 When you look at the ground you seem to be at
- rest. Using the term relative motion explain why
someone in space would see you moving in a circle.
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3 Define speed.
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4 What is the formula for measuring the speed of an
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5 Lance Armstrong can ride his bicycle at speeds of 15 m/s. If he is traveling at this speed, how long will it take him to travel 81.9 meters?
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6 John is growing another crop of corn this year. He plows a row of his field in 90 seconds. If each row is 384 meters long, how fast does John drive his tractor?
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7 Benjamin is learning how to ride his tricycle. His driveway is 30 meters long, and he is not allowed to ride anywhere else yet. If Benjamin travels at 3 m/s, how long will it take him to go from one end
- f the driveway to the other?
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Homework: Motion and Speed
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8 How can you tell that an object is in motion?
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9 What is a frame of reference?
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10 How long does it take a snail to travel a distance
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11 How far (distance) does a cat run if it travels at a speed of 3 m/s for 25 seconds?
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12 A racecar driver frequently drives his racecar at 67 m/s for as long as he can. If he drives his car at that speed for 22 seconds, how far will he travel?
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13 Everyone in Paperville needs their newspaper before 6 a.m. on Monday. If it takes the delivery boy 3 hours to deliver the papers at 12 m/s, what is the distance of the paper route in Paperville?
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Classwork #2: Average vs. Instantaneous Speed & Velocity
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Men’s 100m Dash World Record Activity Sheet
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Homework: Average vs. Instantaneous Speed & Velocity
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14 What is the difference between average speed and instantaneous speed?
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15 What is the average speed of a dog that runs 100 m in 30 s?
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16 You look at your speedometer in the car on a trip to look at your speed. Is this an average speed or instantaneous speed?
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17 List two examples of average speed and two examples of instantaneous speed.
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18 The Admiral train is traveling east at 100 mph and the Alamo train is traveling west at 100 mph. Do they have the same speed? Do they have the same velocity? Why?
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19 Train A leaves New York at the same time Train B leaves California. They are 2900 miles apart. If they both travel at an average speed of 120 mph. A What is the velocity of train A? B What is the velocity of train B? C How long will it take before they meet?
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Classwork #3: Graphing Motion
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Graphing Motion Simulation Activity Sheet
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Homework: Graphing Motion
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20 It is Field Day at your school and everyone is ready for the potato sack race. Each grade has selected one person to enter the race. There were nine checkpoints along the racecourse. Graph the motion of the three contestants using a separate color/line pattern for each contestant.
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Name 10m 20m 30m 40m 50m 60m 70m 80m 90m Susie (6th) 4s 9s 11s 15s 21s 23s 28s 32s 37s Joe (7th) 5s 15s 19s 24s 29s 33s 36s 41s 46s Thomas (8th) 6s 8s 11s 15s 20s 24s 28s 31s 35s
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21 Who won the race?
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22 Who had the fastest speed from 0- 50m?
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23 Who had the fastest speed from 0-70m?
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Classwork #4: Acceleration
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24 Define acceleration.
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25 Write the formula for measuring the acceleration
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26 What is the SI unit of measurement for acceleration?
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27 Explain 3 ways that you can change motion and accelerate.
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28 What is the acceleration of a car that starts at rest and increases its speed to 10 m/s in 2 seconds?
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29 What is the acceleration of an object that starts at 10 m/s and slows to 2 m/s in 4 seconds?
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30 Describe the speed of an object as seen in the acceleration graph below:
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31 Describe the speed of an object as seen in the acceleration graph below:
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Homework: Acceleration
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32 Explain why going around a corner on a bicycle is considered acceleration.
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33 A car increases its speed. Is this acceleration positive or negative? Explain.
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34 What is the acceleration of a rocket that is travelling at 20 m/s and increases it’s velocity to 40 m/s in 4 seconds?
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35 What is the acceleration of a dragster that deploys a parachute when travelling at 33 m/s and slows to rest in 11 seconds?
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36 Describe the speed of an object as seen in the acceleration graph seen below:
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37 Describe the speed of an object as seen in the acceleration graph seen below:
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Classwork #5: Forces and Friction
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38 Define a force.
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39 How are forces involved in changing the motion of an object?
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40 What is the “BIG IDEA” about the relationship between forces and acceleration?
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41 What is the Unit for measuring force in the SI system of measurement?
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42 Calculate the net force in the diagram seen below:
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43 Define friction and explain its effect on motion.
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44 What is static friction?
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Homework: Forces and Friction
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45 A force is a push or a pull acting on an object. How do forces affect motion when the forces are a) balanced, and b) unbalanced?
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46 What happens to the motion of any object that feels an unbalanced force?
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47 What types of friction occur when you ride a bike through a puddle?
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Classwork #6: Gravity and Equilibrium
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48 In your own words, define the law of gravitation.
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49 What is the formula for measuring the weight of any object?
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50 Why is the weight of a barbell smaller on the moon compared to the Earth?
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51 What happens to the force of gravity as any 2
- bjects move farther apart?
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52 When is an object said to be in free fall?
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53 Define Equilibrium and relate it to the term balanced forces.
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54 Calculate the Net force acting on the block in the diagram seen below:
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Homework: Gravity and Equilibrium
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55 As we move away from the center of the Earth, what happens to the force of gravity?
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56 Explain why Jupiter’s gravitational constant is stronger than Mercury’s gravitational constant.
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57 What is the weight of a 99 kg man on Earth?
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58 Why does an object accelerate when it falls toward Earth’s surface?
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59 What happens to the motion of any object that feels an unbalanced force?
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60 If an object is in equilibrium, then the forces must be _____________________?
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61 Calculate the net force acting on the block seen in the diagram below:
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62 Is the object in #50 in equilibrium? Explain.
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Classwork #7: Newton's First Law
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63 Who were the early scientists that first studied/explained motion?
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64 What were some of the advances that Sir Isaac Newton made in the area of physics and mathematics?
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65 Define Newton’s 1st law of motion.
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66 What is the relationship between an object’s mass and the amount of inertia it exhibits? Give an example to answer this question.
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Homework: Newton's First Law
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67 Define inertia.
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68 Which object has more inertia? A boy or an automobile? Why?
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69 In your own words, explain an example of Newton’s 1st law of motion.
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Classwork #8: Newton's Second Law
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70 How does applying a force to an object affect its motion?
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71 What is the acceleration of a 100 kg canoe that feels a force of 1000N?
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72 If the canoe in problem #74 is loaded to have a total mass of 500 kg and the force stays the same at 1000 N, what is the new acceleration?
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73 A tennis ball, 0.314 kg, is accelerated at a rate of 164 m/s2 when hit by a professional tennis player. What force does the player’s tennis racket exert
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74 You push a friend sitting on a swing. She has a mass of 50 kg and accelerates at a rate of 4 m/s 2. Find the force you exerted.
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75 How much force would it take to push another friend who has a mass of 70 kg to accelerate at the same rate of 4 m/s 2?
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Homework: Newton's Second Law
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76 What is the unit of force when completing physics problems?
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77 As the mass of an object increases, what if the effect on the resulting acceleration?
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78 What is the acceleration of a 1000 kg car that feels a force of 5000 N?
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79 What force causes a 1 m/s 2 acceleration of a 5 kg bowling ball?
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80 What is the mass of an object that accelerates at a rate of 3 m/s2 when acted upon by a 30 N force?
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81 A worker drops his hammer off the roof of a
- house. The hammer has a mass of 9 kg, and
gravity accelerates it at the usual 9.8 m/s 2. How much force does the earth apply to the hammer?
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Classwork #9: Newton's Third Law
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82 Define Newton’s 3rd Law.
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83 When forces act upon two objects in contact, explain the forces in terms of “paired forces.”
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84 Explain how a rocket works using Newton’s third law of motion.
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85 Define momentum.
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86 How is momentum similar / different to inertia?
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87 What is the formula and unit for measuring momentum?
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88 What is the momentum of a 10 kg object travelling at 3 m/s?
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89 What is the momentum of a 10 kg object travelling at 6 m/s?
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90 What happens to the momentum of an object if the velocity is doubled?
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Homework: Newton's Third Law
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91 How does Newton’s third law relate to the man jumping out of a canoe as discussed in the lesson
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92 Compare the momentum of a fly and a train travelling at the same velocity.
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93 How does sitting in your chair relate to Newton’s 3rd law of motion?
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94 What is the momentum of a 13 kg shot-put travelling at 3 m/s?
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95 What is the momentum of the same shot-put travelling at 1.5 m/s?
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96 If the velocity of an object is cut in half, what happens to the momentum of the object?
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97 Define “conservation of momentum” and give an example of this principle in the real world.
