Force and Pressure Grade 8

1. Force
WHAT IS THE FORCE PRESENT IN THE
SPACE?
TO ANSWER THIS QUESTION,
SHOULDN’T WE KNOW WHAT
FORCE IS

2. Our Planner of the chapter
• Day 1-Introduction to force, Direction and Magnitude of Force
• Day 2-Types of Force in detail
• Day 3-Introduction to Pressure and some real life examples of
pressure
• Day 4- Fluid Pressure and Atmospheric Pressure

3. What is Force?
• Force is an external agent capable of changing the state of rest
or motion, Direction and shape - size of a particular body. It has
a magnitude and a direction.
• SI Unit: newton (N) EFFECTS OF
FORCE

4. Direction and Magnitude of Force
• The measurement of strength and amount of force is called
magnitude of force.
• Two or more forces on the same object can be applied in the same
direction and opposite direction.

5. Different types of Force
• Force that comes into action after the interaction
between objects is called contact force.
• Force due to without interaction between two objects
is called non-contact force. For example; a magnet
can pull an iron nail from a distance.

6. Contact Forces
Muscular force: The force exerted by the muscles in thae body is called
muscular force
 Frictional force: The force that opposes the motion of an object is called
Frictional force. It occurs due to the contact between two surfaces.
 Mechanical force: The force exerted by a machine is called
mechanical force. It needs an external energy for production.

7. Non Contact Forces
Magnetic force: It is the force exerted by the magnets. Eg:
Force of repulsion and attraction between two magnets, force
exerted by a magnet on a piece of iron or steel

8. Pressure
NOW THAT WE HAVE LEARNT ABOUT
FORCE, LETS LEARN ABOUT ANOTHER
INTERESTING PHENOMENA!!

9. Pressure
• The force acting on per unit area of a surface is called pressure.
• Pressure = Force / Area
• SI unit: N/m2 or Pa
• From above formula, we can say that with same applied force
1. Pressure is directly proportional to force; Force increases pressure
increases.
2. Pressure is indirectly proportional to the area; Pressure decreases
with increase in area and increases with decrease in area.

10. Some Real Life Examples of Pressure
• When we cut an apple, we need to use the sharp edge of the
knife instead of a blunt knife because the sharp edge of the
knife has a small surface area and we need to exert less force
with high pressure to cut the apple.
• 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 a very
small surface area and this enables us to apply a greater
pressure with the applied force.

11. Pressure exerted by Liquid and Gas
• Liquid and gas can also exert pressure on inner walls of the
container in which they are kept.
• When air is filled, a rubber balloon gets inflated from all sides.
This happens due to air or gas exerts pressure over the inner
walls of the balloon.
• Water starts leaking if there is a pore in the bottle. This happens
due to water exerts pressure over the walls of the bottle.

12. Atmospheric Pressure
• 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.
• 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.
• A pressed rubber sucker on a plane surface does not come off
because of atmospheric pressure