Notes: Momemtum CW: Acceleration and Momentum H: The Laws of Motion

Notes: Momemtum

CW: Acceleration and Momentum

H: The Laws of Motion

Momentum 2-18-09

Objectives describe the relationship between mass, velocity, inertia, and momentum relate conservation of momentum to motion in a collision

describe the relationship between mass, velocity, inertia, and momentum

relate conservation of momentum to motion in a collision

What makes an object difficult to stop?

Calculating Momentum The momentum of an object is directly related to its mass and its velocity.

The momentum of an object is directly related to its mass and its velocity.

Mass Mass measures inertia. The mass of an object tells you how much the object resists accelerating.

Mass measures inertia. The mass of an object tells you how much the object resists accelerating.

Nothing will change speed unless acted upon by a force. If it’s sitting still, it will keep sitting still. If it’s moving fast, it will keep moving fast. Only a force can change the velocity of an object .

Velocity Fast objects are also difficult to stop.

Fast objects are also difficult to stop.

Momentum = (mass)(velocity) p = mv

Example A ball of mass 2 kg is moving with a speed of 4 m/s. What is its momentum?

A ball of mass 2 kg is moving with a speed of 4 m/s.

What is its momentum?

Solution Momentum = (mass)(velocity) p = mv

Momentum = (mass)(velocity)

p = mv

p = (2 kg)(4 m/s) p = 8 kg m/s

p = (2 kg)(4 m/s)

p = 8 kg m/s

Example A runner has a mass of 75 kg and is running at 6 m/s. What is his momentum?

A runner has a mass of 75 kg and is running at 6 m/s.

What is his momentum?

Solution Momentum = (mass)(velocity) p = mv

Momentum = (mass)(velocity)

p = mv

p = (75 kg)(6 m/s) p= 450 kg m/s

p = (75 kg)(6 m/s)

p= 450 kg m/s

Momentum is a vector quantity. Its direction is the same as the direction of the object's velocity.

Momentum is a vector quantity. Its direction is the same as the direction of the object's velocity.

Elastic collision Resulting momentum

Two dimensional collision

Knowing the momentum of moving objects helps explain what happens when objects collide with one another.

Although moving objects can collide in many different ways, they have one important thing in common .

Although moving objects can collide in many different ways, they have one important thing in common .

Law of Conservation of Momentum The total momentum before and after the collision is not changed by the collision.

The total momentum before and after the collision is not changed by the collision.

collisions