Two glass marbles click together and bounce apart, each moving about as fast as it did before. The collision seems to have cost the pair nothing. There is a name for collisions like that.
The cost is measured in kinetic energy, the energy of motion you met in earlier grades: more mass or more speed means more kinetic energy. In this topic it stays a comparison; the equation for it comes later in the course.
Here are the marbles again, measured. The marbles have equal masses. Before: marble 1 moves at 2.0 m/s and marble 2 sits at rest.
After: marble 1 sits at rest and marble 2 moves at 2.0 m/s.
The motion swapped. The system's total kinetic energy after the collision equals the total before: the same masses, the same one speed, carried now by the other marble.
When colliding objects bounce apart with the system's total kinetic energy unchanged, we call the collision elastic.
Two steel ball bearings collide and bounce apart, and the system's total kinetic energy is unchanged. Is the collision elastic?
Elastic collisions are the exception in everyday life. Most collisions turn some kinetic energy into sound, heat, or a dent.
Billiard balls make a click you can hear: that click is kinetic energy leaving as sound. Their collisions are almost elastic, never exactly elastic.
Perfectly elastic collisions do happen, between molecules and atoms. Between everyday objects, elastic is an excellent approximation at best.
The deciding feature is the kinetic energy, not the bounce. A collision can bounce the objects apart and still lose kinetic energy; that collision is not elastic.
Two carts collide and bounce apart, but the system's total kinetic energy after the collision is less than before. Is the collision elastic?
Two air-track gliders of equal mass collide and bounce apart. Measurements show the system's total kinetic energy after the collision equals the total before. Classify the collision.
The gliders bounce apart.
The system's total kinetic energy is unchanged by the collision.
Bouncing apart with the total kinetic energy unchanged is the definition of an elastic collision.
The collision is elastic.
Katya says: colliding billiard balls make a click you can hear, so a little kinetic energy leaves the system as sound, and the collision is almost elastic rather than exactly elastic. Is she correct?
Which statement describes an elastic collision?
A tennis ball bounces off a racket. Which measurement settles whether the collision is elastic?
In an elastic collision between two gliders, what happens to the system's total kinetic energy?