Which car rolls down a ramp faster?
Help your child make a fair comparison between two car designs on the same ramp.
Gravity racer: wheels, friction and a fair test
On a ramp, stored height energy becomes motion. Some moves the car forward and some turns the wheels. Friction at the axles and air resistance can affect the travel time too. That is why larger wheels are not automatically faster.
A useful comparison starts with the same ramp and starting point, changing only one design feature. Compare the time to finish first. If you test body shapes next, keep the wheels the same so that you can connect the result to the change you made.
„Which car do you expect to need less time on this ramp?“
Try it together in the lab
- Begin with a prediction. You do not have to agree.
- Change Wheel size from 4 cm to 6 cm; keep the ramp and body unchanged.
- Compare finish times together: a smaller time means a faster trip.
Next comparison: Compare the smooth body with the current body, keeping wheels and ramp unchanged.
Start the labAn activity away from the screen
Release two small toy cars in turn from the same mark on a low, safe ramp without pushing them. Repeat the runs. If the cars differ in several ways, the result alone cannot tell you whether the wheels or the body caused the difference.