Chapter 2 - Sections 3 & 4

Chapter 2 - Sections 3 & 4

Newton’s Laws of Motion and Momentum

• Also known as the LAW of Inertia

• An object at rest will remain at rest unless acted upon by a NONzero net force.

• An object moving at a constant velocity will continue moving at a constant velocity unless acted upon by a NONzero net force.

Newton’s First Law

Inertia• A resistance to change in motion

• Depends on MASSo The greater the mass, the greater the inertia

The greater the force needed to change the object’s motion.

Newton’s 2nd Law of Motion

• An object’s acceleration depends on its mass and on the net force acting on it.

F = Net force

a = Acceleration

m = mass

unit = kg.m/s2

2nd Law continued

More dogs could be added OR passengers can be removed.

Dogs could be removed OR passengers can be added.

Newton’s 3rd Law of Motion

If one object exerts a force on another object, then the second object exerts a force of equal strength in the opposite

directions on the first object.

(For every action there is an equal but opposite reaction.)

Equal and opposite reaction...

What makes a bug go splat? pg 50

A. Air pushes the bug forward. The bug produces this force by pushing backward on the air with its wings, and the reaction force is that the air pushes forward on the bug.

.05kg x 2 m/s2 = .1N

What makes a bug go splat? pg 50

B. Newton’s first law of motion says that objects in motion stay in motion. The car stopped but she kept moving forward.

What makes a bug go splat? pg 50

C. The windshield hits the bug with a 1 N force. NO; Newton’s third law states that for every force, there is an equal and opposite force.

Newton’s 2nd law; The same force acts on both, but the bug has a much smaller mass, so it accelerates much more.

Chapter 2.4Momentum

• Is a property of a moving object that depends on the object’s mass and velocity.

• the more momentum an object has, the harder it is to stop the object or change its direction.

What is Momentum?

Momentum = Mass x VelocityUnit is kg.m/s

Remember: Velocity is speed in a given direction.S = Distance/Time

How is momentum calculated?

Conservation of Momentum...

When a moving object hits another object, some or all of the momentum gets transferred to the other object.

THEREFORE….

Conservation of momentum….

The total momentum of any group of objects remains the same, or is CONSERVED, unless outside forces act on the object.

600 To the right

200 400600 to the right

400 0

200400

400 to the right

to the right2 m/s to the right