Newton’s Newton’s Laws of Laws of MotionMotion

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

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

This is also known as inertia…This is also known as inertia…

..

11stst Law Law

Inertia is an Inertia is an object’s object’s resistance to resistance to a change in a change in motion!motion!

These books will stay here forever unless someone or something causes them to move!

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.

11stst Law Law Once in the air, the Once in the air, the

golf ball will not stop golf ball will not stop unless acted on by an unless acted on by an unbalanced force.unbalanced force.

What are the forces What are the forces acting on the golf ball acting on the golf ball in the air?in the air?

Gravity and air Gravity and air resistanceresistance

What is the other invisible, What is the other invisible, unbalanced force that causes unbalanced force that causes objects in motion slowing down objects in motion slowing down and stopping?and stopping?

Do you remember the 2 main types of friction:Do you remember the 2 main types of friction: Kinetic frictionKinetic friction Static frictionStatic friction

In the absence of a force of friction, the book In the absence of a force of friction, the book would continue in motion with the same speed would continue in motion with the same speed and direction - forever! (Or at least to the end and direction - forever! (Or at least to the end of the table top.) of the table top.)

Newtons’s 1Newtons’s 1stst Law and You Law and You

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

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

22ndnd Law Law

The acceleration of an object The acceleration of an object depends on the mass and the depends on the mass and the force applied!force applied!

22ndnd Law Law

FORCE IS FORCE IS ALWAYS ALWAYS

MEASURED MEASURED IN IN

NEWTONS!NEWTONS!

22ndnd Law Law

How to solve a problem!How to solve a problem!

How much force is needed to accelerate a 1400 kilogram car 2 meters per second/per second?

1. Write the formula1. Write the formulaF = m x a

2. Fill in given numbers and units2. Fill in given numbers and unitsF = 1400 kg x 2 meters per second/second

3. Solve for the unknown3. Solve for the unknown

2800 N

Check Your UnderstandingCheck Your Understanding

1. How much force is needed to accelerate a 66 kg skier 1 m/sec/sec?1. How much force is needed to accelerate a 66 kg skier 1 m/sec/sec?

2. What is the force on a 1000 kg elevator that is falling freely at 9.8 2. What is the force on a 1000 kg elevator that is falling freely at 9.8 m/sec/sec?m/sec/sec?

Check Your UnderstandingCheck Your Understanding

   3. How much force is needed to accelerate a 66 kg skier 1 3. How much force is needed to accelerate a 66 kg skier 1

m/sec/sec?m/sec/sec?

66 N66 N

4. What is the force on a 1000 kg elevator that is falling freely 4. What is the force on a 1000 kg elevator that is falling freely at 9.8 m/sec/sec?at 9.8 m/sec/sec?

9800 N9800 N

Newton’s 2nd Law proves that different masses accelerate to the earth at the same rate, but with different forces.

• We know that objects with different masses accelerate to the ground at the same rate.

• However, because of the 2nd Law we know that they don’t hit the ground with the same force.

F = maF = ma

98 N = 10 kg x 9.8 m/s/s98 N = 10 kg x 9.8 m/s/s

F = maF = ma

9.8 N = 1 kg x 9.8 9.8 N = 1 kg x 9.8 m/s/sm/s/s

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. When upon each other. When you sit in your chair, you sit in your chair, your body exerts a your body exerts a downward force on the downward force on the chair and the chair 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 – air goes interaction – air goes out and the balloon goes out and the balloon goes up.These two forces are up.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 Consider the propulsion of a

fish through the water. A fish fish through the water. A fish uses its fins to push water uses its fins to push water backwards. In turn, the backwards. In turn, the water water reactsreacts by pushing the by pushing the fish forwards, propelling the fish forwards, propelling the fish through the water.fish through the water.

The size of the force on the The size of the force on the water equals the size of the water equals the size of the force on the fish; the force on the fish; the direction of the force on the direction of the force on the water (backwards) is water (backwards) is opposite the direction of the 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, through the air, birds depend on birds depend on Newton’s third Newton’s third law of motion. As law of motion. As the birds push the birds push down on the air down on the air with their wings, with their wings, the air pushes the air pushes their wings up their wings up and gives them and gives them lift.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); the bat forces action); the bat forces the ball to the right (the the ball to the right (the reaction). reaction).

33rdrd Law LawThe reaction of a rocket The reaction of a rocket is an application of the is an application of the third law of motion. third law of motion. Various fuels are burned Various fuels are burned in the engine, producing in the engine, producing hot gases. hot gases.

The hot gases push The hot gases push against the inside tube of against the inside tube of the rocket and escape out the rocket and escape out the bottom of the tube. the bottom of the tube. As the gases move As the gases move downward, the rocket downward, the rocket moves in the opposite moves in the opposite direction.direction.