Bouncing Ball Graph/Quadratic Formula

[Megzzy]

Homework Statement

The graph I have posted is the result of using a motion sensor above a bouncing ball.
I am asked to write a clear interpretation of the meaning of each parameter in the equation Y=At^2+Bt+C.

Homework Equations

Y=Ax^2+Bt+C
y=y0+v0t+1/2at^2

The Attempt at a Solution

http://imageshack.us/photo/my-images/687/screenshot20110902at112.png/
I think relating the above two equations that B is the initial velocity and C is the initial position. "A" however is confusing me.
Also if C is indeed the initial position I'm not quite sure I understand why it is negative.

 

[ehild]

Homework Equations

Y=Ax^2+Bt+C
y=y0+v0t+1/2at^2

X in the first equation should be t. So how is A related to the parameter a ?

The ball moves under the effect of gravity - what is the value of a?

ehild

 

[Megzzy]

sorry didn't see that typo!

a would just be the gravitational acceleration correct? So -9.80 m/s^2?
I'm still confused as to how they relate though. Does that mean A is half that of the gravitational acceleration?

 

[ehild]

Does that mean A is half that of the gravitational acceleration?

Yes.

ehild

 

[Megzzy]

Alright thank you!
I'm just confused as to why it changes (shown on that graph)?

 

[ehild]

The parabola is upside-down, so the A parameter is negative (like the gravitational acceleration, which points downward) A=-9.8/2.

ehild