Title: Forces, Friction and Motion
Introduction
Today we will learn about how the force put on an object determines how it will move when there is
no friction and when there is friction.
1. Click this link: http://phet.colorado.edu/en/simulation/forces-and-motion-basics
This is a screen shot of the website:
2. Click the button that says “Run Now”. It might take a few minutes to load.
The screen will look like this:
3. All answers will be recorded on Quia. You will have to switch between Quia and the PhET
simulation in order to complete all parts of the activity.
Explore- Tug of War
Problem: How do the net forces applied to an object affect its motion?
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Place a small man on each side of the rope.
Hit the “go” button.
Hit the “Return” button.
Hit the “Reset all” button. Click the boxes next to “sum of forces” and “values”.
Try it again with two men on the blue side and one on the red side. Hit “go”.
Hit the “Return” button.
Try some different combinations of men and observe the Sum of Forces and the size and
direction of the forces.
Questions
Answer the questions on the Quia PhET simulation quiz concerning Tug of War.
Explore-Motion
Problem: How does the force applied to an object affect the speed of an object?
Part I- Motion
1. Click the tab “Motion” at the bottom of the screen.
2. Check the boxes next to “force, masses, and speed”
3. Place a box on the skateboard. There are NO frictional forces on this surface.
4. Push the slider below the 0 Newtons box to the right until you reach 200N and then let go.
5. Observe what happens to the box and the man.
6. Hit the orange reset button on the right.
7. Now tap the right arrow to increase the force from 0 Newtons to 200 Newtons (the amount of
push applied to the box). The screen should look like this.
8. Count to 10 seconds and observe the speed (look at the speedometer) and motion of the man
and box.
9. Replace the box with the refrigerator. Repeat steps 7 and 8.
10. Click the “Reset All” button.
11. Explore by using different objects and different applied forces (You can also use the people).
12. Now set the applied force to 300N. How much time does it take for each of the objects listed
to obtain maximum speed with same applied force? Maximum speed is reach when the hand
on the speedometer cannot go any further (and the man falls down!)
13. Use a timer and complete the chart below.
Object
1 crate
2 crates
Refrigerator
Man
Girl
Garbage Can
Mystery Object
Mass
Applied force (Newtons)
300N
300N
300N
300N
300N
300N
300N
Time (Use stopwatch)
Questions: Answer the questions on Quia for Forces.
Explore-Friction
Problem: How does the force applied to an object, and friction affect the speed of an object?
1. Tap on the “Friction” tab.
2. Check the boxes next to “ forces and speed”
3. Place the refrigerator on the screen. Tap on the right arrow until you reach 500 Newtons in the
box. The screen should look like this:
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Observe what happens to the man and refrigerator.
Click the “Reset All” button.
Check the boxes next to “values and speed”
Place the refrigerator on the screen. Tap the right arrow to 500 Newtons of applied force in
the box. Slide the Friction tab (right side box) to “None”.
8. Observe the motion of the refrigerator.
9. Click “Reset All”.
10. Check the boxes next to “values and speed”
11. Place any object on the screen. You can also place the people on the screen.
12. Explore the force of friction by setting the applied force at 500N in the box. Try different
objects and try sliding the friction tab between “None” or “Lots” and observe the changes to
the motion and values of the objects.
13. Try to stop the friction tab to indicate that the friction force arrow is between 100N and 200N.
14. Now try the following objects and complete the table. Fill in the missing values.
Object
Applied Force (N)
Friction Force (N)
Crate
Crate + Man
Garbage Can
200
400
125
250
Net Force (Sum of Forces) (N)
75
50
*You can use the Friction Tab to help you check your answers.
Now, Apply What You Have Learned!
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Just like in the Tug of War, when two forces act in opposite directions you can calculate the
Net Force acting on the object which determines the direction of motion.
Applied Force and Frictional force are two forces acting on the same object but in opposite
directions.
Now, as an example, let’s call all applied forces positive and all friction forces negative. With this idea
in mind, fill in the missing values.
Object
Box
Man
Refrigerator
Girl
Garbage Can
Mystery Object
Applied Force (N)
Friction Force (N)
Net Force (Sum of Forces) (N)
-210
190
274
363
122
100
175
350
-137
200
-50
300
Questions:
Answer the questions on Quia about Friction.
The END!!! Congratulations you are finished.