Place two LEGO rectangular pieces parallel to each other. These pieces should have holes through their sides and measure 1 nub and hole by 8 nubs and holes. At one end, connect the two pieces with a flat LEGO rectangular piece measuring 1 nub by 4 nubs. Do the same on the other end. You now have a rectangular shape that will serve as the frame for the car.
Hold the rectangular frame with one of the short sides facing up and the long sides parallel to each other. Push the LEGO axle piece into the top side hole till it comes out through the hole on the opposite side of the frame. Attach one tire wheel on each side of the axle piece. Plug the LEGO wheel connector pieces into the holes on the opposite end of the car starting from the outer edge of each parallel side. Connect one tire to each wheel connector.
Take the the flat LEGO board piece that measures 16 nubs by 16 nubs and turn it so the nubs are facing up. Connect the two LEGO brick pieces measuring 2 nubs by 4 nubs onto the center top of the flat LEGO board piece. Flip the flat board piece over so the smooth side faces up, and set it on a flat surface. The board will now be at a slight angle to form an incline ramp.
Conduct your experiment by placing the LEGO car at the top of the incline and releasing it. Use the stopwatch to time how long it takes the car to come to a stop. Use the measuring tape to measure the distance traveled.
Test how friction affects the car's speed by placing a sheet of sand paper, with the grit side up, onto the flat LEGO board incline. Send the car down the ramp again. Use the stopwatch and measuring tape to determine if there is a difference in speed and distance when the car meets resistance. Record the results.
Turn the car to face the opposite direction as in the original tests and see how the spinning axle and the fixed axle sides affect the car's speed and distance. Record the results.