Post date: Feb 15, 2014 8:30:58 PM
What changes in motion take place when two particles collide? Simple experiments may be conducted using carts equipped with springs, or using steel balls.
Students are asked to make purely qualitative observations. They are invited to test how good their powers of observations are.
I. Elastic collisions.
(a) Body B is initially stationary (vB1 = 0). Body A is moving to the right with velocity vA1. Assume positive direction is toward the right. After collision, the following are possible scenarios:
(1) If mA = mB, body A stops (vA1 = 0) and body B moves with velocity vB2 = vA1.
(2) If mA > mB, both A and B move to the right. B moves faster than A, vB2 > vA2. Body A moves slower than before collision, vA2 < vA1.
(3) If mA < mB, body A bounces and moves to the left while body B moves to the right.
The velocity equations after collision are then derived from the conservation of kinetic energy and conservation of momentum. The above observations are examined using the velocity equations.
II. Perfectly inelastic collisions. Instead of bumper springs or steel balls, we use carts equipped with sticky masking tapes.
(a) Body B is initially stationary. Body A is moving to the right. After collision, they move off as one unit to the right at slower speed than initial speed of A. v2 < vA1.
(b) Bodies A and B are moving toward each other with equal speed. If mA = mB, the bodies stick together and come to a dead stop.