FORCE & MOTION Instructional Module 6 Dr. Alok K. Verma Lean - - PowerPoint PPT Presentation

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• Dr. Alok K. Verma Lean Institute - ODU

FORCE & MOTION Instructional Module 6

1

MarineTech 2009 - 2011 STEM Preparation through Marine Engineering, Science and Technology Experiences

• Dr. Alok K. Verma Lean Institute - ODU
• Study of different types of forces like Friction force,

Weight force, Tension force and Gravity.

• This Module studies relationship between forces and

the different types of Motion they produce, using Newton’s three laws of Motion.

2

Description of Module

MarineTech 2009 - 2011 STEM Preparation through Marine Engineering, Science and Technology Experiences

• Dr. Alok K. Verma Lean Institute - ODU

Targeted Sols : A-1, 3, 11, 15,G -3, 4, 9 , AII-2,3 ,T-3, AII/T-3, AII/T-2 PH - 5d , 5C , 5E

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Learning objectives Activity Force and motion Identify the forces that cause an object’s motion Tension Calculate tension on string and force acting on it. Hooke's law To verify Hooke's law relation ship between force and elongation Projectile motion How projectile angle effects range and velocity on different masses. Gravity Calculate weight on different planets Acceleration Calculate acceleration on connected

• bjects

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Topics Covered

No Topic Time

1. Force and Motion 2. Balanced and Unbalanced forces 3. Types of Forces 4. Types of Friction. 5. Tension Force 6. Hooke’s law 7. Gravity 8. Mass and Weight 9. Newton's First Law 10. Newton's Second Law 11. Newton's Third Law

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5

Force &Motion

Force: A push or pull that one body exerts on another. Motion: A Change of Position or Location.

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Unit of Force

• Forces are measured in Newton
• A Newton is the force required to

give a mass of 1 kilogram (1 kg) an acceleration of 1 meter per second per second (1 m/s2). It is abbreviated as N.

• 1 N is equivalent to 1 kg-m/s2.

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Different Ways of Measuring Force

• 1. Spring Scale
• 2. Force Meter
• 3. Force Gauges

a) Mechanical Gauges b) Digital Gauges

• 4. Dynamometer

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• Balanced forces do not cause change in motion
• They are equal in size and opposite in direction

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Balanced Forces

F F F F

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• An unbalanced force always causes a change in motion
• They are not equal in size and opposite in direction

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Unbalanced Forces

2F F 2F F

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4 N, left – 10 N, right

Which one is balanced and unbalanced?

4 N, left – 4 N, right

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11

4 N, left – 10 N, right

Which one is balanced and unbalanced?

4 N, left – 4 N, right

Balanced Unbalanced

Answers

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12

Types of Forces

• 1. Normal force
• 2. Friction Force
• 3. Tension force
• 4. Gravitational Force
• 5. Spring Force
• 6. Electromagnetic Force
• 7. Nuclear force

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Weight of block (W) Normal Force (Fn) Friction Force (Ff) It is the force exerted by one surface on another. It is perpendicular to the surface.

Normal Force

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The person is walking on the floor and he slips suddenly. What is the reason? Because of lack of Friction

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Force that opposes motion between two surfaces. Depends on the:

• types of surfaces
• different materials

Normal force (Fn) Coefficient of friction Friction force (Ff)

Ff = m Fn

Friction Force

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Four Types of Friction

• 1. Static Friction: Force that acts on objects that are not moving

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• 2. Sliding Friction: Force resulting when pushing or pulling

an object over a surface

Four Types of Friction

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• 3. Rolling Friction: is the resistance that occurs when a round
• bject such as a ball or tire rolls on a flat surface.

Much easier to move object.

Four Types of Friction

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• 4. Fluid Friction: Solid moving through a liquid or a gas
• Force of a fluid friction is always less than sliding friction
• The resistance that a body experiences in fluid is knows as

Drag force. This is proportional to square of velocity of a body.

Four Types of Friction

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Coefficient of Friction (µ) (mu): It is the ratio of the force

• f friction between two bodies and the force pressing them
• together. We use the symbol µ (Greek alphabet).

Value of µ depends on the two surfaces involved and material they are made up of. Example: Teflon on steel has a low coefficient of friction. µ = 0.04 Rubber on concrete has a high coefficient of friction. µ = 1.0

Coefficient of Friction

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Coefficient of Friction (µ) can be calculated experimentally by the following formula:

Calculation of Coefficient of Friction

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Weight of block (W) Normal Force (Fn) Friction Force (Ff)

Height Length

µ = Height/ Length

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• 1. The direction of friction is always ________ to the

direction in which the object is moving .

• a. Same b. Opposite c. Unrelated
• 2. When an object is moving faster through a fluid –

what happens to the force of friction on it?

• a. Force of Friction increases.
• b. Force of Friction decreases .
• c. There is no force.

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• 1. The direction of friction is always ________ to the

direction in which the object is moving .

• a. Same b. Opposite c. Unrelated
• 2. When an object is moving faster through a fluid –

what happens to the Drag force?

• a. Drag Force increases.
• b. Drag Force decreases .
• c. There is no force.

Answers

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Hands on Activity - 1 Measure Coefficient of Friction

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Objective: Measuring the coefficient of friction between different surfaces. Materials for class activity:

• 1. A Flat corrugated plastic board to be used as a ramp.
• 2. Square block with six different surfaces.(Copper,Brass,Rubber,

Wood(Rough surface),Wood(Smooth Surface),Cork sheet.

• 3. 12” Ruler.
• 4. 3 dowels.
• 5. Base Stand.
• 6. Square beam with pulley.
• 7. Wooden clamp

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Hands on Activity - 1 Measure Coefficient of Friction

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Assembled Equipment:

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Activity Procedure:

• 1. Put the square block on the top of the ramp in the center with

the surface materials in contact according to the worksheet.

• 2. Gently release the clamp and slide down the centre post

raising the ramp until the block starts to slide.

• 3. Lock the clamp in this position.
• 4. Measure the height and length of the inclined plane and enter

in the work sheet.

• 5. Calculate the coefficient of friction between the surfaces using

the formula: µ = Height/Length

• 6. Repeat the steps for other five surfaces on the block and

record height and length on the worksheet for each surface combination.

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S.No Slide surface material Block Surface material Length Height Average Length Average Height Coefficient of Friction = Height/Length 1 Plastic Copper 2 Plastic Brass 3 Plastic Rubber 4 Plastic Wood (Rough Surface) 5 Plastic Wood (smooth) 6 Plastic Cork

Work Sheet

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Tension Force

The tension force is directed along the length of the wire and pulls equally

• n

the

• bjects
• n

the

• pposite ends of the wire.

Tension is the magnitude of the pulling force exerted by a string, cable, chain, or similar object

• n another object

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Objective: Calculate Tension force in the string and

• bserve in the tension protractor.

Materials for class activity:

• 1. Tension Protractor
• 2. Vertical Square stick
• 3. Ruler.
• 4. String.
• 5. Weight 300 grams.
• 6. Weight 200 grams.
• 7. Weight 100 grams.

Hands on Activity - 2 Tension Force

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Free Body Diagram

T = Tension in the string F = Force in the horizontal arm

Hands on Activity - 2 Tension Force

W= mg Y X T θ Y X W= mg T θ Sum of all the forces in the x and y direction should be zero F

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Free Body Diagram Hands on Activity - 2 Tension Force

Y X W= mg T θ Sum of all the forces in the x and y direction should be zero

Sum of all the forces in the y direction ∑Fy = 0 T Sin(θ) – W = 0 Sum of all the forces in the x direction ∑Fx = 0 F – T Cos(θ) = 0

T = Tension in the string F = Force in the horizontal arm F

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33 Suspended Mass (kg) W = mg (N) ∑Fy = 0 T Sin(θ) – W = 0 Tension (T) (N) ∑Fx = 0 F – T Cos(θ) = 0 Force (F) (N)

0.3 0.2 0.1

Work Sheet

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Hands on Activity - 2 Tension Force

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10 Minutes

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Force of attraction between any two objects in the universe. Gravity Force Increases

• As mass increases
• As distance decreases between two objects

Gravity

g earth= 9.81m/s2

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MASS & WEIGHT Mass: Mass is a measure of matter.

• Mass is constant.
• m = mass (kg)

Weight: Weight is a force. Weight is not constant. The weight

• f an object depends on location

with respect to the Earth’s surface W = mg W = Weight (N) m = Mass (kg) g = Acceleration due to gravity(m/s2)

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38

Comparison of Weight on Earth and Mars

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To find gravity force on different Planets

Class Exercise - 1

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• 1. The amount of matter in an object is called its weight
• a. True b. False
• 2. The mass of an object is 20 kg on earth, its weight is
• a. 196 N b. 200 N c.76 N d. 96 N
• 3. An object has a weight of 30 N on earth. A second object

weighs 30 N on the moon, which object has greater mass?

• a. The one on the earth
• b. They have the same mass
• c. The one on the moon
• d. Not enough information provided

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41 41

• 1. The amount of matter in an object is called its weight
• a. True b. False
• 2. The mass is 20 kg on earth and its weight is
• a. 196N b. 200N c. 76N d. 96N
• 3. An object has a weight of 30N on earth. A second object

weighs 30N on the moon, which object has greater mass?

• a. The one on the earth
• b. They have the same mass
• c. The one on the moon
• d. Not enough information provided

Answers

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42

It states that the Elongation of a spring is in direct proportion with the load added to it as long as this load does not exceed the elastic limit. Elastic Limit: The maximum stress that can be applied to a Spring without producing permanent deformation

Hooke's Law

Spring Stiffness (N/m) Force (N) Elongation (m)

F = k x

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Objective: To verify Hooke's Law (Relation between force & Elongation) Materials for class activity:

• 1. 10N/m Spring
• 2. 20N/m Spring
• 3. 40N/m Spring
• 4. Weights (5 Hooke's law apparatus
• 5. 50g, 100g, 200g and 500g)

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Hands on Activity - 3 Hooke's Law

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Activity Procedure:

• 1. Hang the 10 N (Red) spring from the notch on the support

arm

• 2. Align the top surface of the washer with zero on the scale
• 3. Hang the specified weight from the spring
• 4. Measure the stretch of the spring and note the values in the

work sheet

• 5. Repeat the steps for additional weights according to the

worksheet

• 6. Repeat the above steps for 20 N (Blue) and 40 N (Green)

spring.

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No Weights (grams) Force(N) Elongation(cm) 1 2 3 4 No Weights (grams) Force(N) Elongation(cm) 1 2 3 4 No Weights (grams) Force(N) Elongation(cm) 1 2 3 4

Spring Stiffness 10 N/m Spring Stiffness 20 N/m Spring Stiffness 40 N/m

Work Sheet

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Hands on Activity - 3

To Verify Hooke’s Law (Relationship between Force & Elongation)

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Velocity: Velocity is the rate of change of position

• The velocity v of an object moving through a

displacement (Δ x) during a time interval (Δ t) is described by the formula:

VELOCITY

Units = meters/sec

Time Travel nt Displaceme Total Velocity 

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ACCELERATION

Acceleration: Acceleration is defined as the rate of change of velocity. The acceleration is the ratio between the change in velocity and the time interval. Units = meters/sec2

Time Travel y in velocit Change

• n

Accelerati 

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• When an object is thrown

into the air, its motion is affected by gravity and wind resistance.

• It follows a parabolic path

as shown on the right.

• At the maximum height,

the vertical component of velocity becomes zero and changes direction.

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Projectile Motion

Range VX VY Height(H)

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Slow projectile - shoot a monkey Fast projectile - shoot a monkey

Fast Projectiles travel longer distances

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• Objective: To observe how projectile angle affects distance

and velocity of different masses.

• Materials for Class Activity:

1.Catapault

• 2. Two balls of different masses. (17 grams , 25 grams)
• 3. Stop Watch
• 4. Measuring Tape

51

Hands-on Activity - 4 Projectile Motion

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Activity Procedure:

• 1. Arrange the equipment such that the ball will land in a safe

area by calculating the maximum distance it might travel

• 2. Place the ball in the catapult
• 3. Start the gun of the catapult at 38 degrees
• 4. Release the ball and note down the time taken when it

touches the ground by using Stop watch

• 5. Repeat the Step 4 for angles 62 , 84 and note down the

values in worksheet 1 provided

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Assembled Equipment: Free Body Diagram

Vy Vx V V = Velocity Vx = Velocity in Horizontal direction Vy = Velocity in Vertical direction

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NO Angle(θ ) degrees Distance (meters) Time of flight(Sec) Vx = V Cos(θ) D1 D2 T1 T2 1 38 2 62 3 84 NO Angle(θ) degrees Distance (meters) Time of flight(Sec) Vx = V Cos(θ) D1 D2 T1 T2 1 38 2 62 3 84

Work Sheet

Mass = 17 grams Mass = 25 grams

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Hands on activity - 4 Projectile Motion

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15 Minutes

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Inertia

The tendency of all objects to resist any change in motion. More mass= More inertia Harder to start or stop motion of an object. Less mass = Less inertia Easier to start or stop motion an object

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An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

NEWTON’S FIRST LAW

FORCE No force

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These pumpkins will not move unless acted on by an unbalanced force. Unless acted upon by an unbalanced force, this golf ball would sit on the tee forever.

NEWTON’S FIRST LAW

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• 1. The inertia applies to
• a. Objects that are not moving
• b. Moving objects
• c. Both moving & non moving objects
• 2. An object wants to maintain its state of motion because it has
• a. Inertia b. Velocity c. Speed d. Acceleration
• 3. Why then, do we observe every day objects in motion

slowing down and becoming motionless seemingly without an outside force?

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• 1. The inertia applies to
• a. Objects that are not moving
• b. Moving objects
• c. Both moving & non moving objects
• 2. An object wants to maintain its state of motion because it has
• a. Inertia b. Velocity c. Speed d. Acceleration
• 3. Why then, do we observe every day objects in motion

slowing down and becoming motionless seemingly without an outside force? Ans: It’s a force we sometimes cannot see – Friction.

Answers

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The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass.

Newton’s Second Law

m F m F a

net

     

a m F Fnet     

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• 1. Acceleration is produced by
• a. Forces b. acceleration c. Pressures d. velocities e. masses
• 2. Mary is accelerating her little red wagon when Tom begins

to pull in the same direction effectively doubling the net force

• n the wagon what happens to the Wagons acceleration?
• a. It halves b. It doubles c. It quarters d. It stays the same

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64 64

• 1. Acceleration is produced by
• a. Forces b. acceleration c. Pressures d. velocities e. masses
• 2. Mary is accelerating her little red wagon when tom begins

to pull in the same direction effectively doubling the net force

• n the wagon what happens to the Wagons acceleration?
• a. It halves b. It doubles c. It quarters d. It stays the same

Answers

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65

Find Force, Mass, Acceleration in the given problems

Class Exercise - 2

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Hands on Activity - 5 Acceleration

Objective: To study the impact of force on the acceleration of a cart under varying load conditions Case 1: Mass of cart constant, Varying force . Case 2: Force constant ,Mass of cart varying. Materials for class activity 1. Motion sensor

• 2. Wooden track
• 3. Wooden cart
• 4. Mass hanger
• 5. Washers (mass = 34 grams

= 0.034 kgs)

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Assembled Equipment:

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Activity procedure: Case - 1 1. Place one washer on the mass hanger. 2. Pull the cart back so the mass is just below the pulley. 3. Make sure that the cart is at least 15cm away from the motion sensor. 4. Tap play button to start recording data and release the cart so it moves toward the pulley. 5. Tap stop button to stop recording after it reaches at the end of the track. 6. Record the value of acceleration from Spark and note it in the last column. 7. Place a second washer on the mass hanger and repeat steps 2 to 6. 8. Place a third washer on the mass hanger and repeat steps 2 to 6.

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Suspended Mass M1(KG) W1=M1g=N1

(Newton)

Cart on track M2(Kg) W2=M2g=N2

(Newton)

F=µN2 (Newton) T=M2a+f Theoretical value a=W1-T/M1(m/s2) Experiment values of a (m/s2)

Force = Mass * 9.81N Mass of the cart = 131 grams. Mass of the washer = 34 grams. Coefficient of friction = 0.2 Work sheet Case - 1 Mass of the Cart Constant, Varying Force

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Case -2

• 1. Place two washers in the mass hanger.
• 2. Pull the cart back so the mass is just below the pulley.
• 3. Make sure that the cart is at least 15 cm away from the motion

sensor.

• 4. Tap play button to start recording data and release the cart so it

moves toward the pulley.

• 5. Tap stop button to stop recording after it reaches at the end of the

track.

• 6. Record the value of acceleration from Spark and note it in the

last column.

• 7. Place one washer on the top of the cart and repeat steps 2 to 6.
• 8. Place a Second washer on top of the cart and repeat steps 2 to 6.

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Suspended Mass M1(KG) W1=M1g=N1

(Newton)

Cart on track M2(Kg) W2=M2g=N2

(Newton)

F=µN2 (Newton) T=M2a+f Theoretical value a=W1-T/M1(m/s2) Experiment values of a (m/s2)

Force = Mass*9.81N Mass of the cart = 131 grams. Mass of the washer = 34 grams. Coefficient of friction = 0.2. Work sheet - 2 Mass Cart Varying and Force Constant

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72

Hands on Activity - 5 Acceleration of Connected Objects

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Newton’s Third Law

For every action there is an equal and opposite reaction

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• The rocket exerts a

downward force on the exhaust gases

• The gases exert on equal

but opposite upward force

• n the rocket

74

Action-Reaction Example

FG FR

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Complete the table by writing the reaction for each action.

Class Exercise - 3

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Solve the word puzzle and match the following on force and motion.

Class Exercise - 4