NEWTONS

ALL FORCES HAVE AN EQUAL AND OPPOSITE REACTION.

• meaning a falling boulder is pushed up by the earth with just as much force as the boulder is falling towards the earth.

A GIVEN FORCE EXERTED ON A SMALL MASS PRODUCES A GREATER ACCELERATION THEN

F=-F

F=M/A

IDENTIFYING

FORCE IS AN INTERACTION BETWEEN

Object A interacts with object B

• Action : object A exerts a force on object B
• Reaction : object B exerts a force on object A

SCENARIO - a cAR

• Action : tires pushes the road
• Reaction : road pushed tires.

ACTION EQUALA REACTION

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• Wall pushes back when you push against it.
• The wall hits you as hard as you hit it.

You can not have an action force without a reaction force.

For every interaction between things ,

THE HORSE-CART PROBLEM

•A common problem regarding Newton's third law is the horse-cart problem.

•The cart system - when the farmer is concert about his cart moving

• net force of cart / mass of cart = very real acceleration
• doesn't care about horse

THE HORSE SYSTEM - THE HORSES POINT OF VIEW

• when the horse puts force on the ground, the ground simultaneously puts
• force on the horse.
• when the horse pushes the ground with more force them the force pulling
• the cart- acceleration occurs

THE HORSE CART SYSTEM - THE POINT OF VIEW OF BOTH THE HORSE AND THE CART

• The internal forces cancel and can be neglected
• To move there must be an interaction
• between the horse-cart system and the ground.

Do Action and Reaction Forces Cancel?

they do not cancel to zero, because the external force of an object is simultaneous,

MANY FORCES PAIRS BETWEEN THE MOLECULES IN AN OBJECT MAY HOLD IT TOGETHER

• thus holding it into a cohesive solid, but they play no role in accelerating it
• a force external to the object is needed to accelerate it.

if action and reaction forces are internal to a system,

A FRIEND ON A SCOOTER IS PULLED BY ANOTHER FRIEND. THE FRIEND ON THE SCOOTER ACCELERATES

• The friend on the scooter now pulls back, this affects the friend in the ground
• and not the friend on the scooter.

EXAMPLE 2

• If two people kick a ball at the same time on different sides
• then the forces cancel one another.

EXAMPLE 3

• if one person kicks a ball then the forces goes on
• because the is a reaction and action.

Forces and Interactions

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• the terms push and pull usually invoke the idea of a living exerting a force.
• Newton realized that force is not a thing itself, put part of a mutual action known as
• interaction: between one thing and another
• when you push against a wall, the wall pushes on you as well

EXAMPLE

• the interaction between a hammer and nail; the hammer's force drives the nail through a
• board
• but this is only half of force. The nail has force itself.
• Therefore the hammer and nail become a pair and create exerted force.
• the interaction that drives the nail is the same as the one that halts the hammer.

the hammer and nail example are an example of Newton's third law

Newton's Third Law

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• whenever on object exerts a force on a second object,
• the second objects exerts an equal and opposite force on the first object.
• "to every action there is always an equal opposing reaction."

THE TWO FORCES ARE CALLED:

• ACTION AND REACTION force.
• it does not matter which force is which
• it is important however to know they interact with one another and
• neither force can exist without the other one.
• the forces come in pairs.

EXAMPLE

• When you walk along a street; you are pushing in the street and the street is
• pushing against you with the same force.
• When you are swimming you push the water backwards,
• but the water pushes you forward.

THERE ARE A PAIR OF FORCE ACTING AND INTERACTING WITH EVERY FORCE;

EXAMPLE

• A person walking on ice. The friction will be minimal,
• and may not be able to exert an action force in return.
• Without an action force there will be no reaction,
• causing no result in moving forward because the force is non-existent.

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• Do not get force confused with mass. Force is not something an object has like mass.
• Force is an interaction between one object and another.
• An object may possess the capability of exerting a force,
• but that does not make the object itself force.