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

The term “newton” is usedin honor of Sir Isaac Newton (1642–1727), who is the first to explain the relationship between force and motion. He synthesized the work of Galileo and other scientists into a unifying principle that governs the motions of everything in the universe These are now known as Newton’s laws of motion.

11stst Law :Law of Law :Law of InertiaInertia

An object at rest will stay at rest…An object at rest will stay at rest…

……an object in motion will stay in an object in motion will stay in motion with the same speed and in motion with the same speed and in the same direction…the same direction…

.. unless acted by an outside .. unless acted by an outside force.force.

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

What is inertia?What is inertia?

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 YOU MOVE IT (acted on by an unbalanced force).

Remember: the greater the mass, the harder it is to change motion.

What are the

forces acted on

the object?

Since these two forces are of equal magnitude and inopposite directions, they balance each other. The book is said to be in equilibrium. There is no unbalanced forceacting upon the book, thus, the book maintains its stateof motion (which is at rest). When all the forces acting onan object balance each other, the object will be at equilibrium and will not accelerate.

11stst Law Law

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

What cause the object to stop rolling?

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

Why then, do we observe Why then, do we observe every day objects in motion every day objects in motion slowing down and slowing down and becoming motionless becoming motionless seemingly without an 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 1 stst Law and Law and YouYou

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

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

Upon contact, an unbalanced forceacts upon each car causing it to abruptly stop or decelerate to rest. Passengers wearing their seatbelts share the same state of motion as the car. As the car accelerates the passengers accelerate with it. As the cars collide and abruptly decelerate to rest, so the passengers abruptly decelerate to rest as well. The wearing of the seatbelt assures that the forces necessary for accelerated and decelerated motion of the passengers exist

What would happen if the passengers were not wearing their seat belts and the car was brought to a sudden and abrupt halt by a collision with another vehicle?

22ndnd Law :Law of Law :Law of AccelerationAcceleration

•A net force will cause accelerationObjects acceleration is directly proportional to the net force acting on it and inversely proportional to the object’s mass

Two important concepts:

MASS

•The lesser/smaller the NET FORCE(f) , the SMALLER The lesser/smaller the NET FORCE(f) , the SMALLER the acceleration(a).the acceleration(a).

MASS

Two important concepts:

mass

•The bigger the mass (M), the SLOWER the The bigger the mass (M), the SLOWER the acceleration(a)acceleration(a)

MASS

22ndnd Law LawFORMULAFORMULA

NEWTON = (Kg) ( m/s2)

Force is in Newton or Kg m/s2

22ndnd Law Law

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

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

Sample Problem 1How much force is needed to accelerate a 5 kg massat a rate of 2 m/s2?Givenm = 5 kga = 2 m/s2

SolutionF = m a= 5 kg × 2 m/s2

= 10 kg m/s2

or 10 N

a=?

4. What acceleration will result when a 12 N net 4. What acceleration will result when a 12 N net force applied to a 3 kg object.force applied to a 3 kg object.

5. A net force of 16 N causes a mass to 5. A net force of 16 N causes a mass to accelerate at a rate of 5 m/saccelerate at a rate of 5 m/s22. Determine the . Determine the mass.mass.

6. How much force is needed to accelerate a 66 6. How much force is needed to accelerate a 66 kg skier 1 m/sec/sec?kg skier 1 m/sec/sec?

7. What is the force on a 1000 kg elevator that 7. What is the force on a 1000 kg elevator that is falling freely at 9.8 m/sis falling freely at 9.8 m/s22??

8. How much force is needed to accelerate a 8. How much force is needed to accelerate a 1400 kilogram car 2 meters per second/per 1400 kilogram car 2 meters per second/per second?second?

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

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

33rdrd Law :Law of Law :Law of InteractionInteraction

ACTION: TIRE PUSHES ROADACTION: TIRE PUSHES ROADREACTION: ROAD PUSHES TIREREACTION: ROAD PUSHES TIRE

ACTION: ROCKET PUSHES GAS ACTION: ROCKET PUSHES GAS BACKWARDBACKWARDREACTION: GAS PUSHES REACTION: GAS PUSHES ROCKET FORWARDROCKET FORWARD

33rdrd Law LawAccording 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 exerts chair and the chair exerts an upward force on your an upward force on your body. body.

33rdrd Law LawWhat are the 2 forces What are the 2 forces acted on the picture?acted on the picture?

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 Consider the propulsion

of a fish through the of a fish through the water. A fish uses its fins water. A fish uses its fins to push water backwardsto push water backwards. . In turn, the water In turn, the water reactsreacts by pushing the fish by pushing the fish forwardsforwards, propelling the , propelling the fish through the water.fish through the water.

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

33rdrd Law Law

Flying gracefully through the air, birds depend on Newton’s third law of motion. As the birds push down on the air with their wings, the air pushes their wings up and gives them lift.

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.

A. On the space provided, write the corresponding A. On the space provided, write the corresponding numbernumberof Newton’s law of motion that best explains theof Newton’s law of motion that best explains thefollowing situations:following situations:________1. You need ketchup to spice up your ________1. You need ketchup to spice up your hotdog,hotdog,but it does not flow out of the bottle. Turnbut it does not flow out of the bottle. Turnthe ketchup bottle upside down, shake atthe ketchup bottle upside down, shake athigh speeds and abruptly halt. That shouldhigh speeds and abruptly halt. That shoulddo the trick!do the trick!________2. Birds fly by flapping their wings down, ________2. Birds fly by flapping their wings down, butbutthe wind beneath their wings keep them up.the wind beneath their wings keep them up.________3. New vehicles include headrests as a ________3. New vehicles include headrests as a mandatorymandatorysafety feature to prevent whiplashsafety feature to prevent whiplashinjuries during collisions.injuries during collisions.________4. Taking the elevator from the eighth floor ________4. Taking the elevator from the eighth floor totothe ground floor, you experience blood rushingthe ground floor, you experience blood rushingfrom your head to your feet when thefrom your head to your feet when theelevator quickly stops.elevator quickly stops.________5. Weightlifter lifts a 100 lb weight over his ________5. Weightlifter lifts a 100 lb weight over his head.head.The same weight pushes his arms down.The same weight pushes his arms down.

_____6. The damaging effect of a collision _____6. The damaging effect of a collision betweenbetweena car and a truck will be greater in the car.a car and a truck will be greater in the car.138 Integrated Science138 Integrated Science_____7. While riding a skateboard, you hit a _____7. While riding a skateboard, you hit a stone—stone—abruptly halting the motion of the skateboardabruptly halting the motion of the skateboardand making you fly off the board.and making you fly off the board._____8. Some teens tend to leave their rooms _____8. Some teens tend to leave their rooms inintotal mess until their parents call theirtotal mess until their parents call theirattention about its chaotic state.attention about its chaotic state._____9. Bump car riders experience a change in _____9. Bump car riders experience a change in directiondirectionupon collision with other bump cars.upon collision with other bump cars.____10. A frog forcefully pushes its hind legs ____10. A frog forcefully pushes its hind legs backwardsbackwardsto give it a forceful thrust forward asto give it a forceful thrust forward asit swims through the pond.it swims through the pond.

1.1. Law of InertiaLaw of Inertia2.2. Law of InteractionLaw of Interaction3.3. Law of InertiaLaw of Inertia4.4. Law of InertiaLaw of Inertia5.5. Law of InteractionLaw of Interaction6.6. Law of AccelerationLaw of Acceleration7.7. Law of InertiaLaw of Inertia8.8. Law of InteractionLaw of Interaction9.9. Law of AccelerationLaw of Acceleration10.10. Law of InteractionLaw of Interaction