Name:___________________________________
Forces and Motion
Date:________________________
Getting Started:
1. Google PHET Forces and Motion Basics
2. Click on the 1st hit
3. Click Run Now!
A. Simulation 1: Tug of War
You and some friends are at the park. You find some rope and decide you’d like to play a game of tugof-war. Unfortunately, there are 5 people so you can’t have an equal amount of people on each side.
One of your friends suggests that the two biggest people should be on one side, while the three smaller
people should be on the other side. Do you think this is a fair way to split up teams? Why or why not?
a. Place 2 people that are the same size the same distance away from the cart.
b. Make a prediction about the movement of the cart.
c. AFTER you have observed the actual movement, click on the sum of the forces box at the top
right hand corner of the simulation. Record the number in the data chart.
d. Complete the rest of the chart using the directions given.
Predicted
Movement
Actual Movement
(none, left, right)
Sum of Forces
(0, x-left, x-right)
1. Same size
Same placement on rope
2. Same size,
Different placement on rope
3. Different size
Same placement on rope
Analysis Questions:
1. Describe which scenario(s) showed a balanced force. Did this cause a change in motion?
2. Describe which scenario(s) showed an unbalanced force. Did this cause a change in motion?
3. Now that you have had a chance to experiment with the simulation, go back to the question at the
beginning of the investigation. What do you think would be the fairest way to divide up your friends
for the game of tug-of-war? Be sure to explain your reasoning.
Name:___________________________________
Forces and Motion
Date:________________________
B. Simulation 2: Motion and Friction
a. Motion
i. Click the tab “Motion”
ii. Check all of the boxes
in the top right (force, values,
masses, and speed)
iii. Click the pause button.
iv. Place a box on the skateboard.
Type 200 in the applied force
box. The screen should look like
this:
1. Press the play button. Count to ten, what happens? (Look at the speedometer)
2. Repeat steps 4 and 5 with the refrigerator. (look at the speedometer)
3. Click the “Reset All” button.
4. Repeat steps ii-iv using different objects and different applied forces. You can also use the people.
5. What happens to the speed, does it slow down as different objects are added and the applied force is
different? Describe at least 2 general statements about how the changes you made (different objects,
different applied forces, different people) affected the speed.
a.
b.
6. Why do you think this happens?
7. How much time does it take for 1 crate, 2 crates, a refrigerator, the man, the girl, and the mystery object,
with same applied force get to maximum speed? Maximum speed is reached when the hand on the
speedometer cannot go any further. Open a new browser and type in this link to use the stopwatch.
http://www.online-stopwatch.com/full-screen-stopwatch/ (Suggestion: start the stopwatch, then start the
animation at 1 sec. Subtract 1 sec from the time and record in the table below.)
Object
1 crate
2 crates
Refrigerator
Man
Girl
Mystery Object(present)
Mass
Applied force
(Newtons)
300N
300N
300N
300N
300N
300N
Time (Use
stopwatch)
Name:___________________________________
Forces and Motion
8.
Date:________________________
Do you think the object’s mass determines how long it will take for that object to reach maximum speed
with an applied force of 300 N? Yes or No, Explain your answer.
9. Estimate how much the mystery object weighs based on how long it took to reach maximum speed at
300N?
Part II-Friction
1. Click on the Friction Tab and check the boxes in the upper right hand corner for Forces and Speed.
2. Practice moving the friction scale back and forth to observe the changes.
a. What happens when you set the friction scale to “none”?
b. What happens when you set the friction scale to “lots”?
c. Why do these changes occur?
3. Place the refrigerator on the screen.
Type 500 in the box.
The screen should look like this:
4. What happened? Did the refrigerator move?
5. Complete the table. Fill in the missing values.
Calculate the sum of forces by using the formula:
Sum of Forces = Applied Force – Friction Force
Object
Applied Force (N)
Friction Force (N)
Crate
200
125
Man
472
Refrigerator
51
Girl
363
100
Garbage Can
500
*You can use the Friction Tab to help you check your answers.
Sum of Forces (N)
272
99
375
6. Reset the simulation. Click the “Sum of Forces” and “Values” boxes. Did you get the same numbers
using the above equation?
Name:___________________________________
Forces and Motion
Date:________________________
Analysis Questions:
1. How does the force placed on an object affect how it moves? (Use one of Newton’s laws in your
explanation).
2. Describe a general relationship between the amount of friction and how an object will move.
3. Which type of surfaces reduce friction? Which type of surfaces add friction?
4. Give a real life example of a way to reduce friction.
5. Which type of energy is produced when there is friction?