# Q & A: Trolley on Ramp

Q:
What factors affect the speed of a trolly down a ramp?
- Darda Hireika (age 13)
London UK
A:
There are a few factors affecting the speed of a trolley down a ramp. The trolley changes speed as it goes down the ramp. It starts from 0 speed (not moving at all) and then speeds up as it goes down the ramp. How much it speeds up depends on a number of things.

How steep the ramp is affects how fast it speeds up. The steeper the ramp the faster it speeds up. (If this doesn't make sense, imagine a ball rolling down a board. If the board is almost straight up and down, then the ball is basically falling, so it's speeding up really quickly. But if the board is almost flat with the ground, it will take a lot longer for the ball to roll down it.)

There can also be friction between the wheels and the axles. If the wheels don't turn very easily, then the cart won't speed up very fast.

Also, there is an effect known as air resistance. As the cart moves through the air the cart pushes on the air and the air pushes back on the cart making it speed up less (this is called action and reaction). Air resistance is a bigger effect for things with more surface on them. This is because things with more surface will hit more air molecules. For example a person in a parachute has more air resistance than a person without one, because the parachute has a lot more surface for the air to push on than the person does. This is why parachutes are useful when jumping out of airplanes. (Since the parachute has more surface to it, the air will slow it down a lot more than if the person were just falling.) How much of an effect air resistance has depends on the shape of the cart.

The one thing that doesn't matter at all is how much the cart weighs. You might think that a heavy cart would move faster. But it doesn't. What gravity does is it speeds stuff up. It speeds it up the same amount no matter what the thing is. (If you drop a ball of paper and a rock at the same time from the same height, they'll hit the ground at the same time... you can try this out at home if it doesn't make sense.) The only thing that the weight of the thing effects is how hard gravity has to work to pull it down. (This is called the force of gravity.)

There are other things that will effect the speed of the trolley, but these are some of the big ones.

-dan
-tamara

(published on 10/22/2007)