Forces and

Newton's Law of Motion A force is a push, pull or twist that causes an object to either

Increase its speed (accelerate)

Decrease its speed (decelerate)

Change its direction or

Change its shape

Forces are measured in Newtons What is a Force? There is usually more than one force acting on an object.

Some of these forces may balance by cancelling each other out.

If cancellation is complete then the overall force is zero and can cause no acceleration. You don’t speed up nor do you slow down (Newton’s first Law). You just remain stationary, or keep travelling like you were before. Balanced Forces Newton's First Law of Motion Newton’s First Law examines the forces

on an object that is

At rest

In motion Anything at rest will stay that way unless pushed or pulled.

Example: Place a pen on the desk. Watch what it is doing.

This is known as Inertia Newton’s First Law states Anything that is moving will keep moving at the same speed and in the same direction unless a force changes it. Newton's Law of Motion Further States.... Forces

A force is a push, pull or twist that causes an object to either;

Increase its speed (Accelerate)

Decrease its speed (Decelerate)

Change its direction or

Change its shape

NEWTON’S FIRST LAW OF MOTION

Newton’s First Law states;

Anything at rest will stay that way unless pushed or pulled (Inertia)

(That is, a force is required to get something moving)

Newton’s First Law further states;

Anything that is moving will keep moving at the same speed and in the same direction unless a force changes it. Newton's 2nd Law of Motion Acceleration Acceleration applies to any change in velocity. This may be a change in speed (e.g. from 10 to 20 m/s) or a change in direction (e.g. from north to east). All acceleration requires a force. The bigger the force, the greater the acceleration. Two people pushing a car will be more effective than just one person pushing it. But if the car is a big one, the acceleration will be less: mass affects acceleration. Acceleration Mass is the amount

of matter in an object. It never

changes unless you remove

a bit from it or add more to it.

A 2 kg mass stays as 2 kg

regardless of where it is in

the universe. Mass Something will happen if a force is applied: the object will accelerate and the acceleration will depend on the mass of the object.

Force = mass × acceleration or F = ma

This formula can also be arranged to give:

m = F/a and a = F/m Newton’s Second Law of Motion Newton’s Third Law of Motion Something will happen if a force is applied: the object will accelerate and the acceleration will depend on the mass of the object. Recap

Newton's 2nd Law of Motion For every action force there is an equal and opposite reaction force. Newton's 3rd Law of Motion According to Newton, whenever objects A and B interact with each other, they exert forces upon each other. When you sit in your chair, your body exerts a downward force on the chair and the chair exerts an upward force on your body. There are two forces resulting from this interaction - a force on the chair and a force on your body. These two forces are called action and reaction forces

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# Forces and Newton's Law of Motion

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