Adding a friction sled to a propeller-driven cart

1. Reverse the direction of the propeller and the motor so that it blows toward the cart. To do this, place the white dab of paint facing away from the motor, and reverse the red and black leads.

2. Build a sled to drag behind the cart. Fold up one end of a file card. Make a loop of thread about 20cm long and tape one end of it to the file card.

3. Hook the loop over the bumper. Use clay to add weight to the sled.

4. Connect the SmartWheel to your handheld computer. Refer to Technical Hints to see how to connect the SmartWheel.

5. Start the software to measure velocity. Make the following three measurements one after another with the graph running. You will then have all of your data on one graph, and you can analyze it. Note: because the cart is going backwards, the velocity graph will be upside down.

   1. With no weight on the sled, start the motor and let the cart go for about 3m.

   2. Put some clay on the sled and hook it onto the bumper. Give the cart a push so that it rolls to a stop after about 3m.

   3. With the clay still on the sled, start the motor and let the cart go for about 3m.

6. Save the data to your handheld computer.