Newton's Laws of Motion - Day 2

• Force - A push or a pull

  • You pull a door open

  • You push a basketball away as you make a shot

• Newton (N) - The metric system unit of force

  • It takes approximately one newton (1 N) of force to lift an apple to your mouth

What is Force?

A force can cause an object to:

• Change speed

• Change direction

• Change both velocity and direction

Force and Acceleration

• We use arrows!

• The larger the arrow, the larger the force!

How do we draw forces?

• If forces that are equal in size and opposite in direction are put on an object, they cancel each other out

• The forces are balanced

• The object does not move

Balanced Forces

• Newton’s First Law of Motion – An object in motion will remain in motion, and an object at rest will remain at rest, until a force acts upon it

  • If a ball is moving, it will keep moving until something slows it down

  • If it is not moving, it won’t move until something causes it to move

Newton's First Law of Motion

Friction

• Wait.

• If you roll a ball down the hall, it will eventually stop

• But the Newton’s First Law said it would keep moving!

• What is slowing it down?!

• Friction – a force that resists motion between two surfaces that are in contact

• There is friction between the ball and the floor, so it eventually slows down

Inertia

• What would be easier to push across a floor: a rolling chair or a refrigerator?

  • The chair, because it’s smaller

• Which would be harder to stop moving: a soccer ball, or a linebacker?

  • The linebacker, because he’s bigger

• In both cases, it’s harder to change the motion of objects with more mass

Newton's Second Law of Motion

• When you put a force on an object, it starts to move

  • That means it changes velocity

  • What do we call a change in velocity over time?

  • Acceleration!

• Newton’s Second Law of Motion – when an object is acted on by a net force, it causes a change in velocity in the direction of the force

Newton's Second Law