The science of the grubber kick

breadmonkey

God I hope there are some rugby heads that visit this forum!

Have you ever noticed that after executing a grubber kick, the ball bounces along and then bounces highest on the 3rd *main* bounce?

Can anyone explain?

oq4v3ht0u76kf2

I'd assume it is to do with the momentum of the ball... is it a hard and fast rule? Being a hooker I'd rarely practice kicking, I'm more of a crash ball man. Thinking about it though, it would seem to depend to do with the forward motion of the ball and the angle at which it hits the ground. Must go through some of the DVDs I have now and pay special attention to grubbers.

goodgod3rd

i'd say its the shape of the ball....
the whole <> thing ..
one end hits the ground*im not a player so all guess work!!!* bounces round.. other end hits.. so on the third there is more kenitic energy?

perhaps.

breadmonkey

It can't be gaining kinetic energy, otherwise it would just get faster and faster until it reached the speed of light. And that would hurt if it hit you

goodgod3rd

on the third highest bounce it loses all the energy:
1st bounce..gains some and uses a little.
2nd. gain's some more.. uses a little more (with all the first left over)
3rd (highest/bestist??) uses all energy in the move. when all is used up. falls to ground.

like i say. its a guess... i suggest www.thesciencefourm.com to ask some there. they are real smart!!!

breadmonkey

The ball can't be gaining (kinetic) energy since it's at it's maximum velocity just as it leaves your boot. Or is it?

Unless, of course, it's mass is changing. But that's just silly

breadmonkey

ttt, I want answers people!

nitroboy

well it can actually gain kinetic energy!
Whenever I kick a ball (or anything for that matter) up into the air it generally slows down(reduced kinetic energy) before gravity "kicks" in and then the ball speeds up again(increase in kinetic energy)???
Maybe the oddness that is a rugby ball shape creates its own gravity, who knows!!

Capt'n Midnight

the ball has
potential energy (height)
kenetic energy (speed 1/2 mv2)
rotational energy (spinning)

it will loose total energy all the time from drag and inelastic collisions.
Back in the days of Napolean they used to bounce canon balls off the ground or even skip them off the sea. The bounce would not be very high, a couple of feet but they would still have loads of kenetic energy. Same may be true of the rugby ball that at the 3rd bounce it might be the end of the ball and not the side that touches to give a higher but slower bounce.

I'd doubt that the spinning would affect stability but the first two bounce should have removed any gyroscope effect too.

bozzie

as the shot leaves the foot the direction of the wide sideof the elipse is lateral on the first bounce is starts a rotation from lateral to vertical on the second bounce this motion is increased and by the third/4th kickthe direction of the bulge is vertical and so causes a "kick" into the air