Need Help Understanding Terminal Velocity in Physics Experiment - Urgent!

[thyqwerty]

Help needed on question. URGENT!

Hi,
Basically I'm doing my IB standard physics coursework and i have to write all about an experiment we did.
Its fairly simple, we dropped a ping pong ball from varying heights and measured the height that they rebound to. I found that as the initial height increases, the percentage increase decreases (so graph curves to the right...) (so from 10cm it was 8cm, from 20 its only 16etc...)
I understand that this is to do with terminal velocity etc...
However, for some reason i am really really stuck on finding a logical explanation. Surely if TV was the reason it curved, it would kick in suddenly, therefore a sharp turn in the graph...
I'm actually not that bad at phyics its just that its in for tomorow and am really panicking a bit.
Thanks in advance for any help given :)

 

[kuruman]

...
However, for some reason i am really really stuck on finding a logical explanation. Surely if TV was the reason it curved, it would kick in suddenly, therefore a sharp turn in the graph...

Why should it kick in suddenly? Usually, terminal velocity is reached asymptotically.

 

[thyqwerty]

So it gets closer and closer while never touching it?
so acceleration decreases with time (or height in this case) when nearing terminal velocity...
It that the main reason why the graph curves? Or is it more to do with the energy lost through heat, sound etc...
So how come a ball from 10cm bounces to 80% of its original height but a ball from higher bounces to a lower percentage of its height.

 

[kuruman]

So it gets closer and closer while never touching it?
so acceleration decreases with time (or height in this case) when nearing terminal velocity...
It that the main reason why the graph curves? Or is it more to do with the energy lost through heat, sound etc...

"Terminal velocity" means that the velocity reaches a constant value. When that happens, what do you think the acceleration is?

So how come a ball from 10cm bounces to 80% of its original height but a ball from higher bounces to a lower percentage of its height.

I believe that is the question that your experiment wanted you to figure out. I will give you a hint:

If the ball reaches terminal velocity after it is dropped from, say, 3.0 m and it jumps back up to 1.8 m, to what height will it jump back up after is dropped from 4.0 m?

 

[thyqwerty]

Just that "asymptotically" technically means that it will never reach the asmytote i.e terminal velocity ?
In answer to the question, surely it would alsoo be 1.8 metres too, since in both cases the ball hits the ground at the same velocity therefore the same force so rebounds to the same height ?

 

[kuruman]

Just that "asymptotically" technically means that it will never reach the asmytote i.e terminal velocity ?

Essentially yes. It will need an infinite amount of time (mathematically) to reach terminal velocity, but it comes so close to terminal velocity in a finite time, that it makes no difference for all practical purposes.

In answer to the question, surely it would alsoo be 1.8 metres too, since in both cases the ball hits the ground at the same velocity therefore the same force so rebounds to the same height ?

So is it the height from which the ball is dropped what counts in this experiment or something else? And if it is something else, how does it vary with the height from which the ball is dropped?

 

[thyqwerty]

hmm well the title of the investigation is "how does the initial height effect..." in a very simple way, in which case the basics is to say , that the higher the ball is dropped from the more it bounces...
so would that be:
More g.p.e so more kinetic force and velocity generated, therefore more contact force( is that right ?) when it hits ground, loses some energy because of sound heat etc...

 

[kuruman]

I am sure you will write a fine report. Good luck.

 

[thyqwerty]

ok,
Thanks for all the help,
much appreciated