newton’s laws of motion. learning objectives state newton’s first law of motion. state...

Newton’s Laws of Motion

Learning Objectives State Newton’s first law of motion. State Newton’s second law of motion. State Newton’s third law of motion.

Warm up 10/30 Define these words

inertia

Isaac Newton

“If a horse draws a stone tied to a rope, the horse (if I may so say) will be equally drawn back towards the stone....”

—Sir Isaac Newton

Newton’s First Law of Motion

An object at rest will remain at rest unless acted upon by a nonzero net forceAn 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.an object moving at a constant velocity will continue moving at a constant velocity unless acted upon by a nonzero net force.

Inertia: resistance to change in motion

At rest Constant motion in a straight line

AND

Inertia Depends on MassThe greater the mass of an object, the greater its inertia and the greater the force required to change its motion.

2 13

Newton’s Second Law of Motion

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

Si Unit: Newtons (N)

Newton’s Second Law of Motion

The sled’s acceleration will increase if:

OR

more dogs are added to increase the force.

passengers are removed to decrease the mass.

Newton’s Second Law of Motion

Practice:Practice:

What is the net force on a 1,200-kg race car accelerating at a rate of 3 m/s2?

3,600 N

Newton’s Third 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 direction on the first object.

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

For every action, there is an equal and opposite reaction.

Action

Reaction

Action-Reaction Forces

Force on ballForce on ball

Force on hands

Laws of Motion in Action 1. Use one of Newton’s laws to explain why the driver was thrown forward when she braked.

Newton’s first law says that objects in motion stay in motion. The car stopped, but the driver’s inertia kept her moving forward.

Laws of Motion in Action 2. Use one of Newton’s laws to explain how the seat belt stopped the driver’s body from moving too far forward.

Newton’s third law says that for every action force, there is an equal and opposite reaction force. The driver’s body exerted an action force on the seat belt. The seat belt exerted a reaction force on the driver that stopped her motion.

Laws of Motion in Action 3. Use one of Newton’s laws to determine how much force the driver will need to exert to make it to her appointment on time.

Newton’s second law is represented by the formula F = ma.

F = (1,100 kg)(2 m/s2)F = 2,200 N

Patterns in Newtons Laws

Q: What pattern of motion identifies with the law of inertia?• A: objects resist a change in their motion

Q: What pattern exists in the law of force and acceleration?• A: as force increases, so does acceleration if the mass is

constant• A: as acceleration increases so does force if the mass is

constant• A: As mass increases, acceleration decreases if the force

is constant• A: As mass decreases, acceleration increase if the force is

constant

Patterns in Newtons Laws

Q: What pattern exists in the law of action-reaction?• A: Every action force has a corresponding reaction force

Q: What are the action- reaction forces?• A: Whenever one object exerts a force on a second object,

the second object exerts an EQUAL and OPPOSITE force on the first object.