Always keep safety in mind when conducting your experiment. You can do this by ensuring you are inside, away from people. 

To obtain the raw data, you will need to draw up a table and record the information.

It is suggested you record the weight of the car, the degree of incline, and the speed the car rolls down the slope. The variable will be the speed of the car down the incline.

Remember, consistency is the key. 

If the experiment is not reflecting your hypotheses, troubleshoot and determine what could be going wrong, then try again. A;ways learn from your mistakes.