1. Momentum and Collisions
Elastic and Inelastic Collisions

2. Collisions When two objects come together
In some collisions, the objects stick together
Perfectly Inelastic
In other collisions, the objects separate
Elastic
Total kinetic energy is usually not conserved because kinetic energy is converted to internal energy as the objects deform

3. Perfectly Inelastic Collisions
Perfectly inelastic collision – a collision in which two objects stick together and move with a common velocity after colliding
An arrow sticking into a target
Mass of the first object * initial velocity of the first object + mass of the second object * initial velocity of the second object equals the final velocity * the sum of the two object’s masses
m1v1,i + m2v2,i = (m1+m2)vf

4. Perfectly Inelastic Collisions

5. Perfectly Inelastic Collisions
Remember to assign positive and negative values based on direction
Kinetic energy is not constant in perfectly inelastic collisions

6. Elastic Collisions
Elastic collision – a collision in which the total momentum and total kinetic energy remain constant
m1v1,i + m2v2,i = m1v1,f + m2v2,f
½m1v1,i2 + ½m2v2,i2 = ½m1v1,f2 + ½m2v2,f2

7. Elastic Collisions

8. Inelastic Collisions
Most collisions are neither elastic nor perfectly inelastic
Fall into a third category
Inelastic collisions – the colliding objects bounce and move separately after collision, but total kinetic energy decreases

9. Collisions