Forces and Motion Simulation Lab

Question

Part 1: Net Force
Open the Forces and Motion Simulator and click on the Net Force tab. Turn on the Sum of Forces, Values and Speed indicators.

You’ll see 4 red and 4 blue people below the tug of war cart. Each side has 2 small (50N) people, 1 medium (100N) person and 1 large (150N) person. Complete the orange cells in the data table below by dragging the indicated number of people to each side of the cart and clicking the Go! button.
Trial
Blue Side
Red Side
Sum of Forces (N)
(Magnitude of Net force)
Direction of the Sum of Forces
Acceleration?
(yes or no)
1
2x small people
1x small person
50
Left
Yes
2
2x small people
1x medium person
0
Balanced
No
3
1x medium person
1x large person
150
Right
Yes
4
1x large person
All 4 people
350
Right
Yes
5
1x large person
1x small person
1x medium person
2x small people
0
Balanced
No

Part 2: Friction
Click on the Friction tab at the bottom of the simulator. Check all the options in the yellow box (Forces, Sum of Forces, Values, Masses, Speed) and move the friction slider to Lots

Click the button to apply 50N of force to the crate. Does the crate start to move? No
Draw a freebody diagram of the crate and label ALL forces (symbol, vector, and magnitude). Be sure to consider both horizontal and vertical forces acting on the crate.

Now click the button to increase the force to 150N.
Does the crate start to move? No
What is the horizontal net force on the crate?
0,NN

Are the forces on the crate balanced?Yes
What happened to the friction force as you increased the applied force from 50N to 150N?
Nothing

What type of friction is this?Static
What is the maximum force you can apply to the crate just before it starts to move?
The maximum force that can be applied just before the crate moves is equal to the maximum static friction force.

Continue to click the button just until the crate moves.
What is the horizontal NET force on the crate?
66 N

Are the forces on the crate balanced?No
What type of friction is this?SELECT

Modify your free body diagram from #1, when the crate was at rest, to show the forces acting on the crate as it is moving.

Continue to increase the applied force to 300N.
Describe the motion of the crate.

What is the horizontal net force on the crate?

In what direction is the acceleration? Select One

Once the crate reaches a speed of 40m/s, the person will stop pushing.
Did the frictional force change? SELECT Why or why not?

Are the forces on the crate balanced? SELECT
Describe the motion of the crate.

What is the net horizontal force on the crate?

Answer 1

Part 1: Net Force

| Trial | Blue Side | Red Side | Sum of Forces (N) | Direction of the Sum of Forces | Acceleration? | |-------|----------------------------------|--------------------------------------|-------------------|-------------------------------|---------------| | 1 | 2x small people (50N each) | 1x small person (50N) | 50 | Left | Yes | | 2 | 2x small people (50N each) | 1x medium person (100N) | 0 | Balanced | No | | 3 | 1x medium person (100N) | 1x large person (150N) | 150 | Right | Yes | | 4 | 1x large person (150N) | All 4 people (2x small (100N), 1x medium (100N), 1x large (150N)) | 350 | Right | Yes | | 5 | 1x large person (150N), 1x small (50N), 1x medium (100N) | 2x small people (50N each) | 0 | Balanced | No |

Part 2: Friction

1. Free Body Diagram (Crate at Rest):

   • Forces acting on the crate when it is at rest:
     • Weight ⯈: Downward (gravity) - Magnitude: \( W = mg \)
     • Normal Force ⯅: Upward - Magnitude: Equal to the weight
     • Applied Force (only at 50N or 150N when applied)
     • Friction Force (static friction) - Opposing the applied force, magnitude equal to the applied force when at rest or balanced.

   ![Free body diagram] FBD when crate is at rest

2. Does the crate start to move at 50N?

   • No

3. What is the horizontal net force on the crate when the applied force is 150N?

   • 0N

4. Are the forces on the crate balanced?

   • Yes

5. What happened to the friction force as you increased the applied force from 50N to 150N?

   • Nothing (remained equal and opposing static friction).

6. What type of friction is this?

   • Static friction

7. Maximum force before moving?

   • Equal to maximum static friction force (just below the threshold that was experienced).

8. As you increase the applied force until it moves

   • Horizontal NET force when it starts moving: 66N
   • Balanced forces?: No
   • Type of friction while moving: Kinetic friction.

9. Modified Free Body Diagram (Crate is Moving):

   • Forces acting on the crate when it is moving:
     • Weight ⯈: Downward
     • Normal Force ⯅: Upward
     • Applied Force: (greater than static friction)
     • Friction Force (kinetic friction) - Opposing the direction of motion, steady magnitude less than the applied force.

   ![Free body diagram] FBD when crate is moving

10. Describe crate motion with 300N applied force:

    • The crate moves with constant acceleration due to the net force acting on it.

11. What is the horizontal NET force on the crate at 300N?

    • If friction was at about 34N, then \( 300N - 34N = 266N \).

12. Direction of acceleration: Right (in the direction of the applied force).

13. Frictional force change when person stops pushing at 40m/s?

    • It remains the same (equal to the kinetic friction).

14. Are the forces on the crate balanced?

    • No, there’s a net force acting on the crate.

15. Describe the motion of the crate when forces are unbalanced:

    • The crate is accelerating and moving in the direction of the net force until external force is removed.

16. What is the net horizontal force on the crate later?

    • Remains the same (would be consistent with the applied forces minus friction). If applied force was 300N with a max friction of 34N then resulting net force should be 266N (for example).

Note: Free Body Diagrams mentioned are a conceptual representation. Make sure to draw them accurately according to your visualization based on described conditions.