NewtonNewton’’s s Laws of Laws of MotionMotionhttp://www.youtube.com/watch?v=MAm6LOUnJ80

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).

NewtonNewton’’s Laws of Motions 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. F=MAacceleration. F=MA

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 motionless.motionless.

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 by an unbalanced force unbalanced force (gravity and air (gravity and air – fluid friction), – fluid friction), it would never it would never stop! stop!

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.

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?

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

Objects on earth, unlike the Objects on earth, unlike the frictionless space the moon frictionless space the moon travels through, are under the travels through, are under the influence of friction.influence of friction.

There are four main types of friction:There are four main types of friction: Sliding friction: Sliding friction: ice skating Rolling friction: Rolling friction: bowling Fluid friction (air or liquid): Fluid friction (air or liquid): air or water resistance Static friction: Static friction: initial friction when moving an object

What is this unbalanced force that acts on an What is this unbalanced force that acts on an object in motion?object in motion?

Slide a book Slide a book across a table and across a table and watch it slide to a watch it slide to a rest position. The rest position. The book comes to a book comes to a rest because of the rest because of the presencepresence of a force of a force - that force being - that force being the force of friction the force of friction - which brings the - which brings the book to a rest book to a rest position.position.

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.)

ExamplesExamples

Objects like to keep doing what theyObjects like to keep doing what they’’re re doing!!!doing!!!

NewtonsNewtons’’s 1s 1stst Law and You Law and You

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

Real World Real World DON’T LET THIS BE YOU!!DON’T LET THIS BE YOU!!

BUCKLE UP!BUCKLE UP! http://www.youtube.com/watch?v=d7iYZPp2z

YY

Time For Demonstrations!Time For Demonstrations!

I will complete ALL demonstrations. It is your I will complete ALL demonstrations. It is your job to pay attention carefully and answer the job to pay attention carefully and answer the questions on your sheet.questions on your sheet.

Exit Ticket Exit Ticket

Explain and describe Newton’s first law of Explain and describe Newton’s first law of motion. motion.

What is another word for Newton’s 1st law of What is another word for Newton’s 1st law of motion? motion?

22ndnd Law Law

http://science360.gov/obj/video/642db496-d506-432e-85b4-4e38f75d9142/newtons-three-laws-motion

22ndnd Law Law

The net force of an object is The net force of an object is equal to the product of its mass equal to the product of its mass and acceleration, or F=ma.and acceleration, or F=ma.

22ndnd Law Law

When mass is in kilograms and acceleration is When mass is in kilograms and acceleration is in m/s/s, the unit of force is in newtons (N).in m/s/s, the unit of force is in newtons (N).

One newton is equal to the force required to One newton is equal to the force required to accelerate one kilogram of mass at one accelerate one kilogram of mass at one meter/second/second.meter/second/second.

22ndnd Law (F = m x a) Law (F = m x a)

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

Write the formulaWrite the formula F = m x a Fill in given numbers and unitsFill in given numbers and units F = 1400 kg x 2 meters per second/second Solve for the unknownSolve for the unknown 2800 kg-meters/second/second or 2800 N

NewtonNewton’’s Second Laws Second Law Force = Mass x AccelerationForce = Mass x Acceleration Force is measured in NewtonsForce is measured in NewtonsACCELERATION of GRAVITY(Earth) = 9.8 m/sACCELERATION of GRAVITY(Earth) = 9.8 m/s22

Weight (force) = mass x gravity (Earth)Weight (force) = mass x gravity (Earth)

Moon’s gravity is 1/6 of the Earth’sIf you weigh 420 Newtons on earth, what will you weigh on the Moon?

70 Newtons

If your mass is 41.5Kg on Earth what is your mass on the Moon?

NewtonNewton’’s Second Laws Second Law

WEIGHT is a measure of the WEIGHT is a measure of the force of ________ on the force of ________ on the mass of an objectmass of an object

measured in __________measured in __________

gravity

Newtons

MeasurementsMeasurements

WeightWeight is measured using a is measured using a Spring ScaleSpring Scale MassMass is measured using a is measured using a balancebalance..

NewtonNewton’’s Second Laws Second Law

One rock weighs 5 Newtons.The other rock weighs 0.5 Newtons. How much more force will be required to accelerate the first rockat the same rate as thesecond rock?

Ten times as much

Force and Motion Force and Motion

I will now demonstrate Newton’s Second Law!!I will now demonstrate Newton’s Second Law!!

NewtonNewton’’s Third Laws Third Law

For every action there is an equal and For every action there is an equal and opposite reaction.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 - a force on interaction - a force on the chair and a force on the chair and a force on your body. These two your body. These two forces are called forces are called actionaction and and reactionreaction forces. forces.

Think about it . . .Think about it . . .

What happens if you are standing on a skateboard or a slippery floor and push against a wall? You slide in the opposite direction (away from the wall), because you pushed on the wall but the wall pushed back on you with equal and opposite force.

Why does it hurt so much when you stub your toe? When your toe exerts a force on a rock, the rock exerts an equal force back on

your toe. The harder you hit your toe against it, the more force the rock exerts back on your toe (and the more your toe

hurts).

Action: earth pulls on you

Reaction: you pull on earth

Action and Reaction on Different Masses

Consider you and the earth

NewtonNewton’’s 3rd Law in Natures 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).

Action: tire pushes on roadReaction: road pushes on tire

Action: rocket pushes on gases

Reaction: gases push on rocket

Consider hitting a baseball with a bat. Consider hitting a baseball with a bat. If we call the force applied to the ball If we call the force applied to the ball

by the bat the by the bat the action forceaction force, identify the , identify the reaction forcereaction force..

(a) the force applied to the bat by the hands(a) the force applied to the bat by the hands

(b) the force applied to the bat by the ball(b) the force applied to the bat by the ball

(c) the force the ball carries with it in flight(c) the force the ball carries with it in flight

(d) the centrifugal force in the swing(d) the centrifugal force in the swing

(b) the force applied to the bat by the ball

33rdrd Law Law

Flying gracefully Flying gracefully through the air, through the air, birds depend on birds depend on NewtonNewton’’s third 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.

Consider the flying motion of birds. A bird flies by Consider the flying motion of birds. A bird flies by use of its wings. The wings of a bird push air use of its wings. The wings of a bird push air downwards. In turn, the air reacts by pushing the bird downwards. In turn, the air reacts by pushing the bird upwards. upwards.

The size of the force on the air equals the size of the The size of the force on the air equals the size of the force on the bird; the direction of the force on the air force on the bird; the direction of the force on the air (downwards) is opposite the direction of the force on (downwards) is opposite the direction of the force on the bird (upwards).the bird (upwards).

Action-reaction force pairs make it possible for birds Action-reaction force pairs make it possible for birds to fly.to fly.

Other examples of NewtonOther examples of Newton’’s 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 Law

Consider the motion of Consider the motion of a car on the way to a car on the way to school. A car is school. A car is equipped with wheels equipped with wheels which spin backwards. which spin backwards. As the wheels spin As the wheels spin backwards, they grip the backwards, they grip the road and push the road road and push the road backwards.backwards.

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.

1stlaw: Homer is large and has much mass, therefore he has much inertia. Friction and gravity oppose his motion.

2nd law: Homer’s mass x 9.8 m/s/s equals his weight, which is a force.

3rd law: Homer pushes against the ground and it pushes back.