2. What Is Force ?
• Force Is a Push or A pull
• It Requires 2 objects to start
• It can move A stationary Object
• It can Change Shape And Size Of a
object
4. Effect Of Force
• Force can change the state of motion: An Object can be in two states.
(a) Rest State: When an object is not moving. This means a stationary object is called in
the state of rest. For example –A ball and book kept over the ground and not moving.
(b) Motion State: A moving object is called in the state of motion. For example – a
moving car, a moving ball, etc.
A Force can move a stationary object. A force can speed up, decrease the speed and
change the direction of a moving object. Force can stop a moving object. Finally we can
say that force can change the state of motion.
• Force can change the shape of an object:
1.
When you apply force on an inflated balloon by pressing it using your hand from both
sides, then the force of pressure changes the shape of balloon.
2. You can change the shape of rubber band and spring by stretching it in opposite
direction,
3. You can change the shape of dough into bread by applying force with a rolling pin.
So we can say that forces can change the shape of an object.
5. Contact Force
• Contact force – the force which can start with A physical touch or contact is
known as contact force , it is further divided in 2 groups ,
Muscular – the force which is caused due to actions of muscles of both humans
and animals is known as a muscular force . muscular force is applied only when
there is a interaction with object hence ,is a contact force . like - when we push
the object like school bag or lift the bucket of water, we use the muscular force.
Friction - friction the force of friction always acts on all moving object and
its direction is always opposite to the direction of motion . force of
friction comes into action only after interaction between two objects, thus,
it is a type of contact force. Like - ; when we stop pedaling a bicycle, it
gradually slow down and finally comes to s stop due to force of friction.
6. Non- Contact Force
• Force due to without contact between two objects is called non-contact force. For example; a
magnet can pull an iron nail from a distance.
Magnetic force, Electrostatic force and Gravitational force are examples of non-contact force.
A magnet can exert a force on another magnet without being in contact with it.
The force exerted by a magnet is an example of a non-contact force.
Example: Opposite pole of two magnets attract each other and same pole repel each other.
When a charged body exert a force on another charged or uncharged body is called
electrostatic force.
A charged body attracts an uncharged body.
A positively charged body attracts a negatively charged body and repels a positively charged
body without coming in contact, thus it is a non-contact force.
Gravitation force is exerted by earth, moon, sun and other planets to others.
Earth and other planets attract all objects towards them. Since, earth attracts all objects even
without coming in contact, thus gravitational force is a non-contact force.
Example: When we release an object from a height, it falls over the ground because of
gravitational magnetism of earth.
7. Pressure
• The force acting on per unit area of a surface is called pressure. We can say force
per unit area is called pressure.
Pressure = Force / Area
From above formula, we can say that with same applied force, Pressure is
indirectly proportional to the area, thus pressure decreases with increase in area
and increases with decrease in area.
Example:
(i) When we cut an apple, we need to use the sharp edge of the knife instead of
blunt knife because the sharp edge of knife has small surface area, and we need to
exert less force with high pressure to cut the apple.
(ii) When we put a nail into a wooden board, the pointed end of the nail is kept at
the front. The pointed end of the nail has very small surface area and this enables
us to apply a greater pressure with the applied force.
8. Pressure exerted by Liquid and Gas
• Pressure exerted by Liquid and Gas:
(i) Liquid and gas can also exert pressure on inner walls of
the container in which they are kept.
(ii) When air is filled, a rubber balloon gets inflated from all
sides. This happens due to air or gas exerts pressure over
inner walls of the balloon.
(iii) Water starts leaking if there is a pore in the bottle. This
happens due to water exerts pressure over the walls of the
bottle.
9. Atmospheric Pressure
• Atmospheric Pressure:
(i) Our atmosphere is made of different types of gases. Since gases exert pressure,
thus Pressure exerted by air (present in atmosphere) is called atmospheric
pressure.
(ii) The weight of air in a column of the height of the atmosphere and area 10 cm
× 10 cm is as large as 1000 kg. The reason we are not crushed under this weight is
that the pressure inside our bodies is also equal to the atmospheric pressure and
cancels the pressure from outside.
(iii) A pressed rubber sucker on a plane surface does not come off because of
atmospheric pressure.
