I throw a small hard rubber bouncy ball forward after the second bounce it accelerates faster than the first bounce and the distance travelled is greater than the first bounce…if you dont believe me try it for your self…i thought energy cannot be created or stored…explanations please…:smack:
sorry i mean bouncy ball…
Spin, I expect. The time in which the ball is in contact with the surface is long enough to impart spin to the ball at the first bounce. This may make the ball “jump” away on the second bounce.
I don’t want to hijack, but I believe this may be entirely relevant:
Throwing a bouncy ball (about 4 cm diameter) hard enough at the floor (carpeted) so that it bounces up and hits the ceiling results in ball returning to the thrower after bouncing off the ceiling, starting with a good range of throwing angles (up to around 30 degrees to the vertical, maybe greater).
This requires the ball to completely reverse horizontal direction on the second bounce. I’m thinking that the effects are related.
Any ideas?
I think what happens is:
Most of the time just throwing the ball such it will hit the floor about one step before my feet will add a little backward spin or just no spin. (see below )
The ball will hit under an angle of lets say 70deg. and jump up at a 105deg., a little steeper, because it had the backward spin.
The kinetic energy of the flowing ball was transferred into heat (a little), forward spin (SOME !), bounce back kinetic (most).
Now it already has forward spin.
The second bounce the angles will be 75deg. down and 145deg. up.
(0deg. is horizontal to me, 180deg. is horizontal away from me.)
2nd time energy conversion is heat (same little), forward spin (less* then 1st time !), bounce back kinetic (a little more than last time).
The resulting spin will be grater. The amount converted into spin is less as the ball does not need to be turned “the right way” as in the first time.
If you measure the bounce back height exactly, you would realise see that is substantial less after the second jump compared to the first. But this is difficult to observe.
The forward movement of the ball will be much more the second time, what is easy to see.
Test my hypothesis:
Drop the ball vertically with no spin. Is it jumpier the second bounce?
Throw with intentional forward spin. Is the bouncyness difference 1st to 2nd now less?
Why always backward spin?
I want to throw a small ball. What my limbs do:
- the upper arm lifts a bit = my elbow moves forward 10cm
- the same time my lower arm moves about a quarter circle down
- at the end my hand moves about a 8ths of a circle down
- at the very end my fingers open
2&3 will add a little forward spin to the ball, 1 will reduce that somewhat but 4 will make the ball roll along my fingers and add quite some backward spin.
MummyCave
In the meantime puggyfishs reply was in. My explanation serves also his observation.
Consider how the ball leaves your hand; in most cases, it rolls a little from your palm to your fingertips as it is launched, imparting a slight backspin. If you exaggerate this, it is actually possible to get the ball to bounce back toward you.
That’s true, but if you take my example and observe the angles the ball moves through when it strikes the floor and the ceiling, the change in direction is far greater on the second bounce. The same is true for the observation in the OP. This effect does not require initial spin.
It does require an initial horizontal veloctity. As MummyCave said, dropping a ball vertically is not going to result in anything other than it bouncing up to a proportion of its initial height.
Unless you have done a quantitative measurement (e.g. by coating the ball with ink and measuring the distance between the impressions), I’m inclined to attribute to an illusion. You subconsciously expect the second bounce to be much shorter than the first, so if it greatly exceeds your expectations you are fooled into thinking it bounced farther than the first time.
Because rubber balls are exceptionally ‘grippy’, the spin ‘bounces’ too (i.e. the direction of spin reverses each time the ball bounces), so you throw it with backspin, after the first bounce, it has topspin, after the next bounce it has backspin again and so on, so it is appears to move with alternately long and short bounces. Except that the spin deteriorates faster than the movement of the ball, so by the fourth or fifth bounce, the spin might largeley hav disappeared.
thanks guys
spin is the answer and this effects velocity of the next bounce…and also the distance travelled…energy is not created the formsof energy in the bouncy ball in motion are simply tranferred…I think this is right :smack: