I set up a light gate at the bottom of my ramp. The can was stationary at A and accelerated down the slope to B where the light gate timed how long it took for the can to pass through. The timing works because the can blocks the infra-red light beam for a certain amount of time.
Here's the data we need to work out the speed:
1. I lined up the 0cm end of the ruler with one side of the tin.
2. Then I looked straight down on the reading on the other side of the tin.
Notice that it doesn't look like the 0cm end is lined up correctly anymore. This is an example of parallax error. It is really lined up but doesn't look like it when you change the angle.
3. Here is the time for the diamter of the tin breaking the infra-red beam
4. We can now use velocity = distance/time to calculate the velocity of the tin at B in the original picture, at the bottom of the slope.
5. Next we need an equation:
6. We know the final velocity at B and the initial velocity at A. If we want to calcuclate the acceleration all we need to know is the distance that the tin rolled down the slope. There was a danger of parallax error at the bottom of the slope because the light gate was well above the ruler and I could read it at the wrong angle. So I used a smaller ruler to make sure that 0cm on my big ruler lined up the the light gate.
Then I looked at the top of the slope and got this reading for the distance the can rolled.
7. I put all of the readings into metres and calculated. I foundout that the acceleration was 1.4 m/s/s.
8. Then I realised that as the tin rolled along the floor it slowed down and stopped. I reaised that I could use the same equation to calculate the deceleration from B to C below.
All I had to do was to measure how far it rolled along the floor. Here's the reading
9. Friction caused it to decelerate and stop. This time I got -0.46 m/s/s. The minus sign means slowing down not speeding up. Acceleration is a vector so it can be negative as well as positive.
