Collision between spheres: general result

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Dr Ben Yelverton

Dr Ben Yelverton

5 ай бұрын

Deriving general vector expressions for the velocities of two smooth spheres following a collision. We include both elastic and inelastic collisions, by allowing for an arbitrary coefficient of restitution. Using the zero-momentum frame allows us to simplify the maths a little!
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About me: I studied Physics at the University of Cambridge, then stayed on to get a PhD in Astronomy. During my PhD, I also spent four years teaching Physics undergraduates at the university. Now, I'm working as a private tutor, teaching Physics & Maths up to A Level standard.
My website: benyelverton.com/
#physics #mathematics #mechanics #momentum #collision #coefficientofrestitution #restitution #inelasticcollision #elasticcollision #zeromomentumframe #centreofmass #centerofmass #velocity #vectors #vectoraddition #physicsproblems #conservationlaws #maths #math #science #education

Пікірлер: 4
@Nxck2440
@Nxck2440 5 ай бұрын
If we wanted to allow for rough spheres so that we can have spinning balls, what extra things would we need to know? Can we still use a zero momentum frame since now we will have angular momentum?
@DrBenYelverton
@DrBenYelverton 5 ай бұрын
The coefficient of friction is enough extra information in principle, but the complication is that the frictional force is governed by an inequality (F≤μR) rather than an equation. That makes it hard to deal with analytically, but I've implemented it in a simulation before. The idea is to first apply a normal impulse given by the equation from the video, then compute the tangential impulse that would reduce the relative velocity of the points of contact to zero, clamp this tangential impulse to μ × (normal impulse) if it's too big, then apply it. I suppose you could follow the same logic analytically and come up with some conditions and corresponding equations for changes in tangential and angular velocity, but it would be a little complicated! The ZMF is still very useful in the sense that the calculation of the normal impulse is the same as in the video - the linear momentum will still be zero after the collision even if the balls have angular momentum about their centres of mass.
@darwinvironomy3538
@darwinvironomy3538 4 ай бұрын
@@DrBenYelverton As long the roughness is small or somehow ball are rotating so fast we can assume F = μR right?. does this equation you derived work for 3D? because , following your derivations, there's no assumption regarding the dimension of the problem.
@DrBenYelverton
@DrBenYelverton 4 ай бұрын
@@darwinvironomy3538 The result does indeed work in 3D. If they are rough enough and/or rotating fast enough then F will be equal to μR, but the difficult part is determining what exactly "enough" means here!
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