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Force

+FORCE

Force: is either a push or a pull that acts on an object.

Whenever you bend, twist, stretch or compress something you are using a pushing or pulling force.

Force is an effect which can,

Start motion,

Stop motion,

Change the speed or direction of motion,

Change the shape or size of a body.

+Unit of Force

Force is represented by the symbol F and is measured in Newton (N). The pull of the Earth on a 100 g mass is about 1 N.

+Measuring Force

The force is measured by a spring balance or dynamometer.

+Action and Reaction

For every action force, there is always an equal but opposite reaction force. If an object applies a force on a second object, then the second object will exert an equal but opposite force on the first object.

+TYPES OF FORCE

There are many different kinds of forces:

Gravitational force

Magnetic force

Electrostatic force

Tension

Frictional force

+Gravitational Force and Weight

Gravitational Force: The force of attraction between two objects due to their masses

Gravitational force depends on;

The masses of the objects,

The distance between them.

+Gravitational Force and Weight

Gravitational force is directly proportional to the product of the masses: The greater the masses the greater the gravitational force.

Gravitational force is inversely proportional to the distance between the masses: The larger the distance between the objects the smaller the gravitational force.

The pull of the earth on a 1 kg mass is about 10 N

+Weight

Weight (w): The gravitational force acting on an object. Since it is a force it is measured by a spring scale and its unit is Newton (N).

+How does weight change?

The weight of an object on the earth depends on its distance from the earth's centre.

Near the earth, an object of mass 1 kg has a weight of about 10 N, whereas 22 000 km away from the centre of the earth, the weight of the object reduces to 1 N.

The weight of an object of 1kg weighs most at the poles (9.83 N) and least at the equator (9.78 N). A body having a weight of 600 N at the equator would have a weight of 603 N at the poles

+How does weight change?

+How does weight change?

The weight of an object also changes from one planet to another since g is different for different planets. However the mass of the object is the same in all planets.

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MASS WEIGHT

It is the amount of matter contained in substance

It is the gravitational force acting on an object

It is the same everywhere It changes from place to place

It is measured by equal arm balance

It is measured by spring scale

Its unit is kg Its unit is N

It is a scalar quantity It is a vector quantity

+MAGNETIC FORCE

Magnetic Force is the attractive or repulsive force between the poles of two magnets.

Unlike poles attract each other (a)

Like poles repel each other (b)

+ELECTROSTATIC FORCE

Electrostatic Force is the attractive or repulsive force among electrically charged objects or electric charges such as electrons and protons.

+TENSION

Tension (T): It is the pulling force in a rope or a chain.

+FRICTIONAL FORCE

Frictional force: It is an important force which only acts when two objects are touching and are applying force to one another. It is a force that slows down moving objects and

brings them to rest. It always acts in a direction opposite to the

direction of the force applied to the object. Walking is possible only on a frictional surface. Water also applies a frictional force to the objects

moving in it. Frictional force does not depend on the area of the

rubbing surfaces.

+ The frictional force between the object and

the table depends on two factors;

a) The weight of the object.

b) The roughness of the surfaces rubbing together.