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2015-16 SHC Physics Name: _________________________________Newton’s Laws

FORCES and Newton’s LawsA force is ______________________________________________________.

Force When is it present? Direction/Notes Symbol Units Equation

Forces - Learning Objectives

LO 3.1: I can define a "force" and provide an example.

LO 3.2: I can identify 4 basic force types and describe them as contact or noncontact forces.

LO 3.3: I can draw an interaction diagram for two objects and use it to draw a force diagram.

LO 3.4: When given one force, I can correctly identify its Newton’s 3rd Law pair.

LO 3.5: I can determine whether forces acting on an object are balanced or unbalanced from its motion and/or its force interactions as well as explain and provide examples.

LO 3.6: I can draw force diagrams for objects showing correct sizes and “feeler-dealer” labels.

LO 3.7: Using a written scenario or a force diagram, I can use the equation a = Fnet / m to solve for an unknown quantity.

LO 3.8: I can describe a scenario using force diagrams, velocity graphs, motion maps, words and equations.

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Lab 1: Bowling Balls

As part of our study of motion and forces, in this activity you will tap a bowling ball across the floor using a mallet. When drawing arrows, the relative size and the direction of your arrows are important! To the RIGHT on the paper will represent the positive direction. You will take photos of these actions, and explain them in your lab report. Use your regular camera AND the Motion Shot App.

Scenario Words Motion Map + Mallet Taps

Accelerate (speed up) the bowling ball from rest to a fast speed.

Accelerate (speed up) the bowling ball from rest to a fast speed, using only very gentle taps.

Accelerate (slow down) a fast moving bowling ball to a stop

Accelerate (slow down) a fast moving bowling ball to a stop, using only very gentle taps.

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Keep a fast moving bowling ball moving at constant velocity.

Keep a bowling ball still that started at rest.

Have a moving bowling ball make a sharp left (90°) turn.

Move the bowling ball around the 3 pt. line at a constant speed.

What patterns do you see between the direction the ball is moving, the direction you hit the ball, and the ball’s resulting change in motion?

Finish Lab Report on the e-copy, found in Schoology.

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Demo 1: Interaction Diagrams

Draw a sketch of the scenario presented. Connect each object with a line and initial representing the two objects that are interacting.

Scenario 1: Bird on table Scenario 2: Bird hanging from rod

Scenario 3: Bird being pushed by buggy at constant speed

Station 4: Uh-oh! Bird is falling!

How do you know if two objects are interacting?

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Discussion 1: Types of ForcesGRAVITY FORCE:

1. On the picture on the right, draw an arrow on each person to show the direction of the Earth’s gravitational pull on that person.

2. What causes gravity?

3. Is there a way to shield out the gravitational force or create a gravity-free room? How/Why not?

4. To what extent is gravity caused by the following factors:

a. Earth’s magnetism (circle one)totally largely slightly not at all

b. Earth’s rotation (circle one) totally largely slightly not at all

c. Earth’s atmospheric pressure (circle one)totally largely slightly not at all

d. Earth’s mass (circle one)totally largely slightly not at all

5. The Earth’s gravitational pull on you is…

larger than smaller than the same as

… your gravitational pull on the Earth.

NORMAL FORCE: Bridging demo

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TENSION FORCE: Spring Scales

FRICTION FORCE: Brushes

In summary: Fill out chart on page 1 together

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Discussion 2: Interaction Diagrams- Force Diagrams

Labeling forces with “feeler-dealer” notation.Objects? Force - Type Feeler Dealer Label

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Practice 1: Interaction Diagrams and Force Diagrams

Scenario / Picture Interaction Diagram Force Diagram Force Diagram1. A 5-kg bowling ball is at rest on

the floor.Bowling ball

2. A 5-kg bowling ball is at rest on top of a 2-kg physics textbook which is on the floor.

Bowling ball Textbook

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Scenario / Picture Interaction Diagram Force Diagram Force Diagram3. The 2-kg textbook is pushed up

by a 60 kg man against the ceiling with a force of 25 N.

Textbook Man

4. A person pulls up slightly on a 25 N box resting on a 10-kg table.

Box Table

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15 N

25 N

Lab 2: Newton’s 3rd Law

After you hand-write this activity in class, you will summarize electronically and submit to schoology. PLEASE GET A PHOTO OF EACH ACTIVITY AND DEMO. Be sure ALL partners get the photos.

ACTIVTY 1: (Pulling with the same spring scale)Each partner get a red spring scale. Hook their "S" hooks together, and hold them horizontally so that you can see the N side of the spring scale. Each partner holds a spring scale. One partner is A. The other is B

a. Partner A pulls with 4 N. Partner B does not pull. Describe what you see on the spring scales.

b. Partner B pulls with 4 N. Partner A does not pull. Describe what you see on the spring scales.

c. Now both partners pull with 4 N. Describe what you see on your spring scales.

ACTIVTY 2: (Pulling with different spring scales)Partner A gets a red spring scale. Partner B gets a brown spring scale. Hook their "S" hooks together, and hole them horizontally so that you can see the N side of the spring scale. Each partner holds a spring scale. One partner is A. The other is B

a. Partner A pulls with 4 N. Partner B does not pull. Describe what you see on the spring scales.

b. Partner B pulls with 4 N. Partner A does not pull. Describe what you see on the spring scales.

c. Now both partners pull with 4 N. Describe what you see on your spring scales.

d. What is different about the spring scales (compared with Activity 1)? How does this affect the results?

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ACTIVITY 3: (Rolling Chairs)Place 2 partners on one rolling chair, and one partner on another rolling chair. (aiming to have a "small mass" chair and a "big mass" chair). One person from each chair hold a scale. Face each other, then use the scales to push off from each other. What do the scales read? What happened to your chairs? Why?

Now face each other with the scales touching. Have another person push you down the hallway. What do the scales read while you are moving?

DEMO 4: (Collisions)

Collision when moving slowly.

Collision when moving fast.

DEMO 5: (Videos of Carts)

https://drive.google.com/folderview?id=0B4h2KfPMJ6ONX1BCbUlBcll5SDA&usp=sharing

Watch videos 846 and 849. The rings are the same “stretchiness”. What do you see?

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https://drive.google.com/folderview?id=0B4h2KfPMJ6ONX1BCbUlBcll5SDA&usp=sharing

Practice 2: Newton’s 3rd Law

1. In frustration, Alec gets Henry to hold up his test and punches his fist completely through all of the sheets of paper. Which is greater: the force that Alec’s fist exerted on the paper or the force that the paper exerted on Alec’s fist? Explain.

2. In this photo:

Which experienced more force in this collision – the car or the truck? Why?

3. As you sit in your chair and study your physics (presuming that you do), the force of gravity acts downward upon your body. The reaction force to the force of the Earth pulling you downward is ___.a. the force of the chair pushing you upwardb. the force of the floor pushing your chair upwardc. the force of the Earth pushing you upwardd. the force of air molecules pushing you upwardse. the force of your body pulling the Earth upwardsf. ... nonsense! Gravity is a field force and there is no such reaction force.

4. A golf pro places a ball at rest on the tee, lines up his shot, draws back his club, and lets one rip. During the contact of the golf club with the golf ball, the force of the club on the ball is ____ the force of the ball on the club.

a. greater thanb. less thanc. equal to

5. While driving down the road, a firefly strikes the windshield of a bus and makes a quite obvious mess in front of the face of the driver. This is a clear case of Newton's third law of motion. The firefly hit the bus and the bus hits the firefly. Which of the two forces is greater: the force on the firefly or the force on the bus?

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Demo 2: Hover Soccer BallHover Soccer Ball – NO FRICTION

Before the Push During the Push After the PushInteraction Diagram: Interaction Diagram: Interaction Diagram:

Force Diagram: Force Diagram: Force Diagram:

Net Force Diagram: Net Force Diagram: Net Force Diagram:

Forces Balanced or Unbalanced? Forces Balanced or Unbalanced? Forces Balanced or Unbalanced?

Describe the motion: Describe the motion: Describe the motion:

Motion Map: Motion Map: Motion Map:

Velocity Graph: Velocity Graph: Velocity Graph:

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Toy – FRICTIONMoving at a constant speed Stop pushing Object is Stopped

Interaction Diagram: Interaction Diagram: Interaction Diagram:

Force Diagram: Force Diagram: Force Diagram:

Net Force Diagram: Net Force Diagram: Net Force Diagram:

Forces Balanced or Unbalanced? Forces Balanced or Unbalanced? Forces Balanced or Unbalanced?

Describe the motion: Describe the motion: Describe the motion:

Motion Map: Motion Map: Motion Map:

Velocity Graph: Velocity Graph: Velocity Graph:

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Practice 3: Force Diagrams

A racecar takes off at the start of a race.

Interaction Diagram Force Diagram Forces Balanced or Unbalanced?

Describe the motion:

A cat sits motionless on a rug. Interaction Diagram Force Diagram Forces Balanced or Unbalanced?


A skater moves at constant speed across frictionless ice.



A softball plater slides to a stop at home plate, before being tagged “out”.



A boy pulls a wagon across Interaction Diagram Force Diagram Forces Balanced or 15

grass at a constant speed. Unbalanced?


A bucket of water is being raised from a well at constant speed.



A skydiver has just left the plane and is still speeding up as he falls.



A ball rising in a parabolic trajectory.



Demo 3: Hallway and Chair16

Person on chair being pulled with a small force, equal to the force of friction

Interaction Diagram Force Diagram:

Motion Map:

x vs t graph v vs t graph Forces Balanced or Unbalanced?

Describe Motion:

Person on chair being pulled with a medium force, bigger than the force of friction

Interaction Diagram Force Diagram

Motion Map:


Describe Motion:

Person on chair being pulled with

Interaction Diagram Force Diagram:

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a very large force, larger than last time

Motion Map:


Describe Motion:

Person on chair already moving, stops being pulled

Interaction Diagram Force Diagram

Motion Map:


Describe Motion:

Lab 3: pHet Simulation

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Go to http://phet.colorado.edu/en/simulation/forces-and-motion-basics. Click “Run Now” or “Run in HTML5” for tablets. Choose Acceleration Lab.

Scenario #1:

Check all boxes in yellow area on upper left. Choose a brown crate. Set friction to “None”. Set the applied force to 100 N.

Force Diagram: Net Force (calculate or diagram):

Balanced or Unbalanced?

Quantitative velocity graph: Written Description of Motion:

a = Fnet /mFind the acceleration.

Motion Map:

Scenario #2:

Check all boxes in yellow area on upper left. Choose a brown crate. Set friction to “None”. Set the applied force to 200 N.




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http://phet.colorado.edu/en/simulation/forces-and-motion-basics

a = Fnet / mFind the acceleration.

Motion Map:

How does this acceleration compare to the acceleration in Scenario #1? WHY?

Scenario #3:

Check all boxes in yellow area. Choose TWO brown crates. Set friction to “None”. Use an applied force of 200 N.




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Motion Map:


Scenario #4:

Check all boxes in yellow area. Choose a brown crate, IT BEGINS AT REST. Leave friction as is (be sure you hit “Reset All” or the “rewind” button). Use an applied force of 100 N.





Motion Map:

Why is this happening?

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Scenario #5:

Check all boxes in yellow area. Choose a brown crate, IT BEGINS AT REST. Leave friction as is (be sure you hit “Reset All” or the “rewind” button). Use an applied force of 100 N.





Motion Map:


Scenario #6:THREE PARTS!Check all boxes in yellow area. Choose TWO brown crates. Leave friction as is (be sure you hit “Reset All” or the “rewind” button). PART 1: Use an applied force of 450 N, let the speed get about halfway up the speedometer.

PART 1 Force Diagram: Net Force (calculate or diagram):


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PART 2: REDUCE the applied force to 250 N.



PART 3: REDUCE the applied force to 0 N.




a = Fnet / mFind the acceleration FOR EACH PART SEPARATELY.

Motion Map:

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Practice 5: Putting it all together1. A 50 kg box starts at rest and is pushed by a man. Draw a clearly labeled force diagram for the box,

showing correct sizes and “feeler-dealer” labeling.

Are the forces balanced or unbalanced in the direction of motion?

Describe the motion of the box in words.

Draw a motion map for the box moving for 5 seconds.

Calculate the net force acting on the box (including direction!). Show your work mathematically or with a diagram.

Calculate the acceleration of the box. Show your work.

Draw a QUANTITATIVE velocity vs. time graph if the box is moving for 5 seconds.

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How fast is the box moving at the end of 5 seconds? Explain your reasoning.

How hard would the man have had to push to have the box move with a constant speed? Explain your reasoning and draw a force diagram.

How would the motion of the box been different if the mass were the same, but the man pushed with a value greater than the force of friction? Explain.

2. A refrigerator is moving to the right with a constant speed of 2.5 m/s, when the man suddenly reduces his push to 100N.

Draw a clearly labeled force diagram for the refrigerator, showing correct sizes and “feeler-dealer” labeling.

Are the forces balanced or unbalanced in the direction of motion?Describe the motion of the refrigerator in words.

Draw a motion map for the refrigerator moving for 4 seconds.

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Calculate the net force acting on the refrigerator (including direction!). Show your work mathematically or with a diagram.

Calculate the acceleration of the refrigerator. Show your work.

Draw a QUANTITATIVE velocity vs. time graph if the refrigerator is moving for 4 seconds.

How fast is the refrigerator moving at the end of 4 seconds? Explain your reasoning.

How hard would the man have had to push to continue moving the refrigerator at a constant speed? Explain your reasoning.

How would the motion of the refrigerator been different if the man pushed with the same 100 N force, but the refrigerator was less massive? Explain.

How would the motion of the refrigerator been different if the mass were the same, but the man pushed with a value greater than the force of friction? Explain.

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