In: Physics
1. Mathematically explain in Detail how Newton's cradles work. Be able to use your understanding of how Newton's cradles work to create a physics equation/formula that can be used in any situation.
Newton's cradle works based on conservation of energy and
momentum.
Consider the simplest Newton's cradle with only two spheres.
Consider that each sphere has a mass m.
The first sphere is raised and released. It will have a velocity V.
When the first sphere hits the second one, consider that the second
sphere move with velocity Vs and the first sphere recoil with a
velocity Vr
Using conservation of momentum, mV = mVs - mVr
V = Vs - Vr ...(1)
Using conservation of energy,
1/2 mV2 = 1/2 mVs2 + 1/2
mVr2
V2 = Vs2 + Vr2
...(2)
Substituting (1) in (2),
(Vs - Vr)2 = Vs2 + Vr2 ..
Vs2 + Vr2 - 2Vs Vr = Vs2 +
Vr2
- 2VsVr = 0
Vr = 0 since Vs can not be zero.
So, there is no recoil velocity for the first mass. This can be
extended to Newton's cradle with many spheres. When the momentum
and energy is conserved, velocity will be exchanged. The sphere at
rest exchange its velocity with the sphere that hits it.