Momentum and Collisions

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