# Homework Help: Velocity against height graph?

1. Oct 7, 2006

### smileandbehappy

Hi, I am currently doing my a-level coursework on Parachutes. I have got a set of results for my first parachute by dropping the parashute from a determined height and then timing how lond it takes to hit the ground, and thus using the v=s/t formula to calculate the average velocity.

My graph is pretty much linear! I was thinking that it would be curved - is my graph wrong?

I will attatch my graph - if it looks awful would someone be kind enough to tell/show me what it should look like (there was a lot of error in my experiment so this is why I am worrying, and I need an A)

Thank you very much.

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2. Oct 7, 2006

### semc

dude u are right the graph should be a log curve instead of y=x.However,u use v=s/t for ur graph.this means that u are not taking air drag into consideration so i think that should be the reason

3. Oct 7, 2006

### smileandbehappy

I'm not quite sure I understnad what you are saying. So that I can try and explain this in my write up, would you please be kind enough to explain: 1) Why the graph should be a log curve? (an equation which indicates this would help alot), 2) Why would me using the equation for average velocity lead to me gaining an anomolous graph, when what I wish to show is the average velocity again height?

Thanks again.

4. Oct 7, 2006

### semc

well i am not quite sure but i think u are trying to ask why the graph is a log graph but not y=x right?okay... lets say u drop a marble from the sky,the instant u release the marble,gravity will pull it down so it will accelerate down right?however there is also the air resistance which increases as velocity increases.so there will be a point where this drag balances the gravity pull meaning it does not accelerate anymore and this velocity is the terminal velocity.so you know why the velocity does not increase linearly now?
is that alright?

5. Oct 7, 2006

### smileandbehappy

Sorry, I obviously havn't explain myself very well. I just wanted someone to look at the graph and say if they thought it was the correct shape. However you are right in saying that after a certain height the graph should level of.

6. Oct 7, 2006

### semc

oh sry for saying so much then :tongue: