9.4 - elastic + inelastic

what is an elastic collision?

collision in which there is no loss of kinetic energy

what is inelastic collision?

collision in which there is less kinetic energy after the collision than before

when dropping a ball from a given height, what height will the ball reach after bouncing back from an elastic collision?

it will return to the initial height

when dropping a ball from a given height, what height will the ball reach after bouncing back from an inelastic collision?

a much smaller height than the initial height it was dropped from

when is a car crash an elastic collision?

in very low speed impacts provided no damage is done

when is a car crash an inelastic collision?

• if the collision causes damage to the vehicles

• if colliding vehicles couple

why is a car crash an inelastic collision when the vehicles are damaged?

bcuz some of the initial kinetic energy is transferred to the surroundings

why is a collision an inelastic one when the objects couple?

bcuz some of the initial kinetic energy is transferred to the surroundings

how can we tell if a collision is elastic or inelastic?

by calculating the kinetic energy of each object before and after the collision

for a ball being dropped from a given height, what is the kinetic energy immediately before impact?

• kinetic energy immediately before impact = loss of potential energy through height H

• E_k = g p e

for a ball being dropped from a given height, what is the kinetic energy immediately after impact?

• kinetic energy immediately after impact = gain of potential energy through height h

• E_k = g p e

how do we find the change of kinetic energy for ball being dropped from a given height?

here

• fraction of the initial kinetic energy that is recovered as kinetic energy after the collision

• h / H

for a ball being dropped from a given height, why is the change of kinetic energy h / H?

• kinetic energy immediately before impact = g p e from height H

• kinetic energy immediately after impact = g p e through height h

• energy change, when testing collision type, = kinetic energy after the collision recovered from initial kinetic energy / initial kinetic energy

• therefore h / H

how do we find the change of kinetic energy for a collision between two objects?

E_k = ½ m v² , used to find the initial and final kinetic energy

is total energy conserved in all collisions, including inelastic?

yes, always

why is total energy conserved in all collisions, including inelastic?

following conservation laws for momentum and energy, and providing no other external forces act, total energy in a system is always conserved. kinetic energy may be transferred into other energy stores within the system, explaining inelastic collision