chapter 7 force and motion form 2

8/2/2019 CHAPTER 7 Force and Motion Form 2

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CHAPTER 7

FORCE ANDMOTION


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Definition ofForceA force is defined as a push or

a pull. We use a pushing forceto push a trolley. We use a

pulling force to open door.


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What aforce can do

to object?

Change itsspeed

Move it Stop it

Increase or

decrease itsspeed

Change itsposition

Change itsshape


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Pushing Force

Pushing a pram

Hitting a shuttle-cockwith a racket

Cutting a loaf ofbread


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Pulling Force

Stretching aspring

Climbing a tree

Lifting a pail of water


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Types Of Force

Magnetic force

A magnet possesses magnetic force.

Magnetic force attracts iron, nickel and cobalt.A magnet has two poles a north pole and asouth pole.

Like poles repel each other. Unlike poles attract each other.


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The magnetic force is strongest at the poles.

A freely suspended magnet always comes to restin a north-south direction, with its north polepointing towards the Earths north pole.


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Gravitational Force

An object falls because it is pulled by the Earth.

The force of the Earth pulling an object towardsits centre is called the force of gravityorgravitational force of the Earth.

Theweight of an object is the gravitationalforce pulling it.

An object weight slightly heavier at the polesthan at the equator because the poles are nearer

to the centre of the Earth.the Earths gravitational force is about six timesgreater than that of the Moons.


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Electrostatic Force

When a plastic ruler is strongly rubbed with apiece of wool, both the ruler and the piece ofwool become charged with an electrostaticforce.

One object becomes positivelycharged whilethe others becomes negativelycharged.

A charged object (positively or negativelycharged) attracts an uncharged object.

Like charges repel each other.Unlike charges attract each other.


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Frictional Force

Africtional force is produced when 2 surfacesrub against each other.

A frictional force produces heat and can start afire, e.g. striking a match to get a fire.

A frictional force acts in the direction oppositeto that of motion. Hence, a frictional force slowsdown motion.

A frictional force wears out the surface is

contact.


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Measuring Force

The unit of force

The SI unit for measuring force is the newton(N).

A force has magnitude, i. e. size.

Weight of 1 kg 10.0 N

Weight of 100 g 1.0 NWeight of 1.0 g 0.01 N


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Force is measured in Newton (N) by using aspring balance or a compression balance.

A spring balance is works on the principle thatthe extension of the spring is directlyproportional to the force pulling it.

Spring Balance


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A graph showing the extension of a springagainst the force pulling it is a straight line

originating from zero. This is true only if the force is not too large.

Force(N)

0 1 2 3 4 5 6

Extension

(cm)

0 2 4 6 8 10 12


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Graph of extension of spring against force

chapter 7 force and motion form 2

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