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A2 Coursework Help Needed

Hi, I'm currently doing my A2 physics coursework on projectiles and I'm having trouble explaining the patterns in my results. The experiment involves releasing balls from a ramp (with a launch ramp attached to the bottom) at different distances from the base of the ramp. I've attached the main graph which shows how increasing the displacement affects the range of the ball.

I've calculated the expected results if there was no drag (the dashed line on the graph) and I've carried out the experiment on a ping-pong ball, a plastic ball and a metal ball of similar size.

What I expected to see was that the metal ball, since it travels at a greater velocity, would experience more drag and would be the furthest from the dashed line, since drag is proportional to v^2. However, the metal ball seems to experience the least drag and the ping-pong ball which travels the slowest seems to experience the most.

Can anyone explain why this would be the case? It seems logical that the faster the ball is moving, the less drag would affect it but this seems to contradict the drag equation :s-smilie:

Any help would be appreciated. Thanks.
physicscworkgraph.JPG72.2KB
Reply 1
Avatar for Henerz
Henerz
7
Yes, surely you would expect the metal ball to always go further than the ping-pong ball. (i.e. what you have)

My reasoning is as follows: Without drag, all the balls would go the same distance (as the balls are given initial GPE, which is converted to KE before the ball leaves the bench. (Do I understand the experiment correctly?) thus initial velocity is independant of mass. (0.5mv^2=mgh)

All the balls will experience the same drag (a force) as they are all approximatly the same size & shape and have the same speed. So, by Netwtons Second law, if the ball is more massive (the metal ball) it will experience less of an acceleration for the given drag force, be slowed less and have a greater range. The ping pong ball has a greater retardation for the given force so has a reduced range.

I sence I've got the wrong end of the stick?
Reply 2
Avatar for ryanwilk
ryanwilk
OP
Henerz
Yes, surely you would expect the metal ball to always go further than the ping-pong ball. (i.e. what you have)

My reasoning is as follows: Without drag, all the balls would go the same distance (as the balls are given initial GPE, which is converted to KE before the ball leaves the bench. (Do I understand the experiment correctly?) thus initial velocity is independant of mass. (0.5mv^2=mgh)

All the balls will experience the same drag (a force) as they are all approximatly the same size & shape and have the same speed. So, by Netwtons Second law, if the ball is more massive (the metal ball) it will experience less of an acceleration for the given drag force, be slowed less and have a greater range. The ping pong ball has a greater retardation for the given force so has a reduced range.

I sence I've got the wrong end of the stick?


Thanks for replying. That does make perfect sense actually, I was assuming the metal ball had a highest launch speed which is obviously not the case :rolleyes:

Oh well, thanks again :smile:
Reply 3
Avatar for Drummy
Drummy
10
I was about to reply with something similar.

If you drop a ping pong ball and a metal ball with the same dimensions the latter will hit the floor first. For any given speed it will experience the same amount of drag but that drag force will have less affect due to its greater mass.

Imagine playing badminton with a metal shuttlecock!

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