User's Manual

Dynamics Cart Magnetic Damping Experiment 3: Predicting Terminal Velocity

Equation 3 assumes that magnetic drag is the only source of friction. A real cart is

also affected by friction that is not proportional velocity, but is constant as long as the

cart is moving. If this additional frictional force is f

, then the net force on the cart is

(eq. 4)

and

(eq. 5)

The addition of f

does affect the slope of the v versus a graph, but it does add a ver-

tical offset (or “Y-intercept’) equal to .

In this part of the experiment, you will use the motion sensor to record v and a as the

cart slows down after you push it on a level track.

Set-up

1. Make the track level.

2. Attach a motion sensor to the left end of the track.

3. Attach the Magnetic Damping Accessory to the cart.

4. If you are using a plastic cart, add about 250 g of mass, so that the total mass is

about 500 g. (Additional mass is not necessary with a metal cart.)

5. Place the cart on the track with the Magnetic Damping Accessory away from the

motion sensor.

6. Adjust the magnets to be about 1 mm above the track. Check to make sure that

the magnets do not touch the track when you push the cart swiftly.

Important: After you have adjusted the magnets, do not readjust them for the remainder of the

experiment.

Experiment set-up for Terminal Velocity, Part I

Sensor, Interface, and Software Set-up

For detailed information about setting up your motion sensor, interface, and software, refer to the

instructions supplied with those products.

1. Connect the sensor to your interface.

2. Prepare a graph (or graphs) to display Position, Velocity, and Acceleration versus

time.

3. Take some test data and adjust the sensor so that it can measure the cart’s position

up to a distance of about 1 m. Delete the test data.

Leave the sample rate at the motion sensor’s default of 10 Hz.

net

ma bv– f

–= = for v 0>()

-----

a–

----–=

b⁄–