Newton’s Newton’s Laws of Laws of MotionMotion

CHAPTER 10, Sections 2-5 CHAPTER 10, Sections 2-5 NotesNotes

I.I. Law of Inertia Law of Inertia II.II. F=M x A F=M x A III.III. Action-Reaction Action-Reaction

While most people While most people know what Newton's laws know what Newton's laws say, many people do not say, many people do not know what they mean (or know what they mean (or simply do not believe what simply do not believe what they mean.) they mean.)

Newton’s Laws of MotionNewton’s Laws of Motion

11stst Law Law – An object at rest will stay at – An object at rest will stay at rest, and an object in motion will stay rest, and an object in motion will stay in motion at constant velocity, unless in motion at constant velocity, unless acted upon by an unbalanced force.acted upon by an unbalanced force.

22ndnd Law Law – – Force equals mass times Force equals mass times acceleration.acceleration.

33rdrd Law Law – – For every action there is an For every action there is an equal and opposite reaction.equal and opposite reaction.

11stst Law of Motion Law of Motion (Law of Inertia) (Law of Inertia)

An object at rest will stay An object at rest will stay at rest, and an object in at rest, and an object in motion will stay in motion motion will stay in motion at constant velocity, at constant velocity, unless acted upon by an unless acted upon by an unbalanced force.unbalanced force.

11stst Law Law Inertia is the Inertia is the

tendency of an tendency of an object to resist object to resist changes in its changes in its velocity: velocity: whether in whether in motion or motion or motionlessmotionless.. These pumpkins will not move

unless acted on by an unbalanced force.

11stst Law Law Once airborne, Once airborne,

unless acted on unless acted on by an unbalanced by an unbalanced force, it would force, it would never stop! never stop!

The unbalanced The unbalanced force would be force would be gravity and air, gravity and air, which are fluid which are fluid friction.friction.

11stst Law Law

Unless acted Unless acted upon by an upon by an unbalanced unbalanced force, this golf force, this golf ball would sit on ball would sit on the tee forever. the tee forever.

Newton’s 1Newton’s 1stst Law Law

Why then, do we observe Why then, do we observe every day objects in motion every day objects in motion slowing down and becoming slowing down and becoming motionless seemingly without an motionless seemingly without an outside force?outside force?

It’s a force we sometimes cannot see – It’s a force we sometimes cannot see – friction.friction.

Newton’s 1Newton’s 1stst Law and You Law and You

Don’t let this be you. Don’t let this be you. Wear seat belts.Wear seat belts.

Because of inertia, Because of inertia, objects (including you) objects (including you) resist changes in their resist changes in their motion. When the car motion. When the car going 80 km/hour is going 80 km/hour is stopped by the brick stopped by the brick wall, your body keeps wall, your body keeps moving at 80 m/hour.moving at 80 m/hour.

22ndnd Law – F= M x A Law – F= M x A

22ndnd Law Law

Acceleration depends on the Acceleration depends on the object’s mass and the net force object’s mass and the net force acting on the objectacting on the object

22ndnd Law Law

A A decreasedecrease in mass causes an in mass causes an increaseincrease in in accelerationacceleration

AA increase increase in mass causes a in mass causes a decreasedecrease in in accelerationacceleration

Example - A golf cart will go a lot faster with Example - A golf cart will go a lot faster with 2 people instead of 5 people!2 people instead of 5 people!

33rdrd Law Law

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

33rdrd Law Law According to Newton, According to Newton,

whenever objects A and whenever objects A and B interact with each B interact with each other, they exert forces other, they exert forces upon each other. upon each other.

When you sit in your When you sit in your chair, your body exerts chair, your body exerts a downward force on a downward force on the chair and the chair the chair and the chair exerts an upward force exerts an upward force on your body. on your body.

33rdrd Law Law

There are two forces There are two forces resulting from this resulting from this interaction - a force interaction - a force on the chair and a on the chair and a force on your body. force on your body.

These two forces are These two forces are called called actionaction and and reactionreaction forces. forces.

Newton’s 3rd Law in NatureNewton’s 3rd Law in Nature Consider the propulsion of a fish through Consider the propulsion of a fish through

the water.the water.

A fish uses its fins to push water A fish uses its fins to push water backwards. backwards.

In turn, the water In turn, the water reactsreacts by pushing the fish by pushing the fish forwards, propelling the fish through the forwards, propelling the fish through the water.water.

The size of the force on the water equals The size of the force on the water equals the size of the force on the fish; the the size of the force on the fish; the direction of the force on the water direction of the force on the water (backwards) is opposite the direction of the (backwards) is opposite the direction of the force on the fish (forwards.)force on the fish (forwards.)

33rdrd Law Law Flying gracefully Flying gracefully

through the air, birds through the air, birds depend on Newton’s depend on Newton’s third law of motion. third law of motion.

As the birds push As the birds push down on the air with down on the air with their wings, the air their wings, the air pushes their wings up pushes their wings up and gives them lift.and gives them lift.

Other examples of Newton’s Other examples of Newton’s Third LawThird Law

The baseball forces the The baseball forces the bat to the left (an bat to the left (an action.)action.)

The bat forces the ball The bat forces the ball to the right (the to the right (the reaction.) reaction.)

33rdrd Law Law• The reaction of a rocket is an The reaction of a rocket is an

application of the third law of application of the third law of motion. motion.

• Various fuels are burned in the Various fuels are burned in the engine, producing hot gases. engine, producing hot gases.

• The hot gases push against the The hot gases push against the inside tube of the rocket and inside tube of the rocket and escape out the bottom of the tube. escape out the bottom of the tube.

• As the gases move downward, the As the gases move downward, the rocket moves in the opposite rocket moves in the opposite direction.direction.