Friction, Forces, and Motion

Purpose: In this lab, we will explore the relationships between forces and motion, both with and without friction. As we will see, friction can change the nature of a problem because of its dependence on other forces.

Equipment: This lab will be performed on your computer using java-based simulation software from PhET. You may access the program through your browser here:https://phet.colorado.edu/sims/cheerpj/forces-1d/latest/forces-1d.html?simulation=forces-1d.

Background: We have discussed the nature of forces and their relation to motion in class. In this lab, we will explore forces on a variety of objects, under a variety of different conditions. This will let us develop a more complete view of forces, and will let us explore the ramifications of Newton's three laws of motion.

Procedure: Open the "Forces in One Dimension" PhET program. Once the program has loaded, make it full screen, then open all four graphs - position, acceleration, force, and velocity. On the right-hand side of the screen, turn off friction. On the left-hand side of the screen is a box for the amount of force applied by the person. Enter 10 N, but do not start the simulation.

Sketch a free-body diagram of the forces on the filing cabinet.

What is the net force (magnitude and direction) on the filing cabinet? What is the filing cabinet's acceleration in the absence of friction? How much force (magnitude and direction will the filing cabinet apply to the person? How far will the filing cabinet move in 20 s?

Now click "Go" on the right-hand side of the screen. Watch the how the plots change through time. After 20 s (on the horizontal axis of the plots), click "Pause". How do the results from the graphs line up with your predictions?

Attach an image of the plots here. From Word, you may do this by selecting Insert-Screenshot-Screen clipping from the menu at the top of the page.

Click "Clear" to return to the original position. Turn on friction. You may keep the default values for the coefficients. What is the maximum value of the static friction on the filing cabinet? Once the cabinet is moving, what will the value of kinetic friction be?

Sketch the free-body diagram of the forces on the filing cabinet.

If the force applied to the cabinet by the person is 400 N, what will the net force on the cabinet be?

Now set the force from the person to be one Newton more than the maximum static friction. Describe what will happen to the filing cabinet.

What will its acceleration be once it is moving? How fast will it be moving when it reaches the house? How long will it take to reach the house?

Now click Go. Click Pause when the cabinet reaches the house. Do the plots agree with your predictions? If not, why not?

Attach an image of the plots here. From Word, you may do this by selecting Insert-Screenshot-Screen clipping from the menu at the top of the page.

Now let's say the filing cabinet is being pushed across the ground on the Moon. Click Clear to reset the Cabinet's position. On the right-hand side of the screen, you will find a box labeled Gravity. Use the slider bar to adjust the gravitational acceleration to that on the Moon. What value is this in your box?

In the absence of friction, how far will the box go in 20 s with 10 N of force applied? Is this more or less distance than in the frictionless case on Earth? Why?

Run the simulation with 10 N of force and no friction. Do the plots agree with your predictions? If not, why not?

Attach an image of the plots here. From Word, you may do this by selecting Insert-Screenshot-Screen clipping from the menu at the top of the page.

Now turn friction back on. What is the maximum value of the static friction on the filing cabinet? Once the cabinet is moving, what will the value of kinetic friction be?

Sketch the free-body diagram of the forces on the filing cabinet.

If the force applied to the cabinet by the person is 400 N, what will the net force on the cabinet be?

Now set the force from the person to be one Newton more than the maximum static friction. Describe what will happen to the filing cabinet.

What will its acceleration be once it is moving? How fast will it be moving when it reaches the house? How long will it take to reach the house?

Now click Go. Click Pause when the cabinet reaches the house. Do the plots agree with your predictions? If not, why not?

Attach an image of the plots here. From Word, you may do this by selecting Insert-Screenshot-Screen clipping from the menu at the top of the page.

Now change the values to anything you like (non-zero). Enter the values you have chosen below.

Mass:

Gravity:

Static Friction:

Kinetic Friction:

How much force must be applied to overcome friction? If one Newton more force is applied, what will the net force on the object once it begins moving? What will its acceleration be? How long will it take to reach the house? How fast will it be moving when it reaches the house?

Set up the scenario and click go. When the object reaches the house, click pause. Attach an image of the plots here. From Word, you may do this by selecting Insert-Screenshot-Screen clipping from the menu at the top of the page.

Briefly explain what changing the gravitational force will do to friction on level ground. Why does this happen? How will this change on a hill?