Chapter-7 Momentum and Impulse - Winthrop Chemistry

Chapter-7 Momentum and Impulse 1 Momentum 2 Impulse 3 Conservation of Momentum 4 Recoil 5 Elastic and Inelastic Collisions 6 Collisions at an Angle: An Automobile Collision Momentum, p

In everyday life, the word momentum is used to describe changes in the flow of a game or leads in elections. In physics, the momentum p of an object is the product of the objects mass m and velocity v: Momentum = Mass x Velocity Momentum is a vector quantity that points in the same direction as the velocity. SI Unit of Linear Momentum: kilogram meter/second = (kg m/s)

A bowling ball and a tennis ball with the same momentum Q: If the velocity of an object is doubled, its momentum is multiplied by____________ its kinetic energy is multiplied by ___________ a.1 b. 2

c. 3 d. 4 e. 8 Impulse, J The impulse J of a force is the product of the average force and the time interval t during which the force acts: Impulse is a vector quantity and has the same direction as the average force.

SI Unit of Impulse: newton second = (N s) Impulse = Change in momentum Momentum and Impulse A tennis ball bouncing off the floor. There is a rapid change in the direction of the velocity when the ball hits the floor. The floor

delivers the impulse to the tennis ball. Baseball Q: Why batters swing when they hit a ball? A: To increase the time of contact

Catching an Egg Q: An egg is thrown at you. How can you catch it without breaking it? Conservation of Momentum The principle of conservation of momentum helps us understand collisions such as above. The total momentum of an isolated system remains constant (is

conserved). Isolated means there are no net external forces. Demo: Try this box 7.2 Recoil and Rocket Motion Q: Why does a shot gun slam against your shoulder when

fired? Q: How can a rocket accelerate in empty space? Starting from rest, two skaters push off against each other on smooth level ice, where friction is negligible. The mothers mass is 100 kg and the childs is 50 kg. If the

mother moves away with a velocity of 2.5 m/s, west, find the recoil velocity of the child. Two Skaters Push off Collisions are often classified depending on how the total kinetic energy changes during the collision:

Collisions 1. Elastic collisionOne in which the total kinetic energy of the system after the collision is equal to the total kinetic energy before the collision. 2. Inelastic collisionOne in which the total kinetic energy of the system is not the same before and after the collision. 3. Partially inelastic collision is one in which some

energy is lost, but the objects do not stick together after the collision. 4. Perfectly inelastic collision is one in which the objects stick together after the collision. A greatest portion of energy is lost here. Collision Problems in One Dimension 1. A freight car rolling down the track at 3 m / s collides with four identical freight cars that were initially at rest. Calculate the speed of the coupled cars after the collision.

2. A 2000 kg car collides with a 1500 kg car that was initially at rest. The two cars lock together and move off after the collision at a speed of 6 m / s. Calculate the speed of the 2000 kg car before the collision. 3. A football player of mass 100 kg with a speed of 3.0 m / s collides head-on with another football player of mass 85 kg who was initially moving in the opposite direction with a speed of 5.0 m / s. The second player tackles the first and they become entangled into the equivalent of a single mass. Determine the direction and the magnitude of the velocity of the two players after the collision.

Collisions at an Angle Automobile Collision: Analysis