Bouncing ball and coeff. of restitution

[fisico30]

Dear Forum,

in the coefficient of restitution lab, a ball is drop from a certain height and the bounce height is measured to eventually calculate the coefficient of restitution COR...

Why should the initial height always be measured from the bottom of the ball and not from the top? Why does it matter? Does it give more precise results?

It should not matter as long as the bounce height is recorded using the top of the ball as reference...

thanks
fisico30

 

[rcgldr]

You want to know how far the ball drops and bounces back up (the distance travelled) on each cycle. If you're measurements also include the balls "height" at the moment of contact with the ground, then it doesn't matter where you take your measurements from, as long as you're recording the distance vertically traveled on each bounce. You'd need to avoid measuring the top of the ball when it is compressed.