Force & Fan Carts

A. Motion from rest
Turn on the fan but put your hand in front of the cart so that it does not move.

1. Draw a free body diagram for the cart/fan system. Label all forces by identifying: a) the type of force, b) the object on which the force is exerted, and c) the object exerting the force.

2. How would your free body diagram change if you were to remove your hand from the front of the cart? Explain.

3. Suppose that the cart moves away from the sonic ranger, starting from rest, while the fan supplies a constant force. Predict what the velocity vs. time and the acceleration vs. time graphs would look like. Explain.

4. Test your prediction

a. Compare your graph with your prediction on the previous page. Resolve any discrepancies.

b. Use the velocity graph to describe the acceleration of the cart. Explain how you arrived at your answer. What can you say about the net force on the cart?

c. Compare the accleration measured from the velocity graph with the average value measured from the acceleration graph. Do they agree? Account for any discrepancies. Record both accelerations below.

 

B. There and back
Suppose that you push the cart so that the initial velocity is in the opposite direction of the force of the fan and towards the sonic ranger. Assume that the friction is negligible.

1. Draw two free body diagrams below. On the left, draw one for the cart/fan system on its way toward the sonic ranger. On the right, draw one for the cart/fan system after it turns around.

2. Predict the shape of the velocity and acceleration graphs for this situation. Sketch your predictions on the graphs on your whiteboards.

 

C. Motion of a fan cart with friction
Suppose again that you push the cart so that the initial velocity is in the opposite direction of the force of the fan. However, now do not assume that the friction is negligible.

1. Draw two free body diagrams. On the left, draw one for the cart/fan system on its way toward the sonic ranger. On the right, draw one for the cart/fan system after it turns around.

2. Predict the shape of the velocity and acceleration graphs for this situation. Sketch your predictions on the graphs from above with different colors.

D. Do the experiment

1. Do the experiment. Is there friction present? How can you tell?

2. Increase the mass of the cart and repeat the experiment. What happens?

3. Use the data from the first experiment to find the coefficient of friction