Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: DoctorBeaver on 26/04/2007 08:43:03

Title: More balls
Post by: DoctorBeaver on 26/04/2007 08:43:03

This is inspired by PaulFr's "Bouncing a ball on the moon" thread.

When I was younger I had 1 of those super-bouncy balls (I can't remember exactly what they were called). I don't know if they're still around. These balls would bounce seemingly forever, barely losing any height on each bounce.

1 thing I noticed about them was if I spin when I bounced the ball it would rebound in the direction you'd expect it to. But the next time it bounced, it would rebound in the opposite direction. That effect would continue almost until the ball stopped bouncing. It was like a pendulum going from side to side.

So, my question is - what is it about those balls that makes them so bouncy and causes the side-to-side effect?

I've not noticed this effect with other rubber balls. Is it that they don't do it or just that I haven't noticed it?

Title: More balls
Post by: another_someone on 26/04/2007 11:55:24

The amount of bounce will depend only on the elasticity of the material.  Less elastic materials will lose more energy on each impact.

The issue of spin is valid for any ball, however hard or elastic - I can have a very hard ball bounce higher than the release point by imparting sufficient spin to it.  The reason why you wont get the oscillation is because you are again losing too much energy on each impact, so you rapidly lose the energy both of the spin and of the vertical motion.

Title: More balls
Post by: daveshorts on 26/04/2007 15:01:16

This is very related to a kitchen science experiment we did last year.

the guy who did it, Hugh Hunt, has a really interesting website on this sort of subject
http://www2.eng.cam.ac.uk/%7Ehemh/movies.htm#superballs

Title: More balls
Post by: DoctorBeaver on 30/04/2007 13:46:15

Fascinating site. Thanks, Dave  [8D]

Title: More balls
Post by: tony6789 on 09/05/2007 16:49:37

yea its pretty sweet learn something new every day!

Title: More balls
Post by: JimBob on 09/05/2007 22:57:12

This happens to balls that are not soft as well IF the surface they hit is soft - the opposite of the  rubber mentioned. Ever played pool, billiards or snooker? The second bank after hitting the ball with "english" (imparted spin) causes the ball to have an opposite reaction to the reaction off of the first bank.