1. B.J.P.S Samiti’s
M.V.HERWADKAR ENGLISH MEDIUM HIGH SCHOOL
CLASS 8th : FORCE AND PRESSURE
Program:
Semester:
Course: NAME OF THE COURSE
Staff Name: VINAYAK PATIL 1
2. FORCE – A PUSH OR A PULL
• Actions like picking, opening, shutting, kicking, hitting,
lifting, flicking, pushing, pulling are often used to describe
certain tasks. Each of these actions usually results in some
kind of change in the state of motion of an object.
• In science, a push or a pull on an object is called a force.
• Thus, we can say that the motion imparted to objects was
due to the action of a force.
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4. FORCES ARE DUE TO AN
INTERACTION
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• An interaction of one object with
another object results in a force
between the two objects.
• Example: Suppose a man is
standing behind a stationary car
the car does not move, If he
pushes the car that is, he applies
a force on it. The car may begin
to move in the direction of the
applied force.
7. TYPES OF FORCES
• There are two main types of forces they are
Contact forces
Non - contact forces
Contact force: Force exerted by one object on another
when they are in contact with each other.
Contact forces are of two types they are
1) Muscular force
2) Force of friction
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8. Non - contact force: Force exerted by one object on
another without any contact with each other.
Non - Contact forces are of three types they are
1) Magnetic force
2) Electrostatic force
3) Gravitational force
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9. MUSCULAR FORCE
• The force resulting
due to the action of
muscles is known as
the muscular force.
• Animals like bullocks,
horses, donkeys and
camels are used to
perform various tasks
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10. FORCE OF FRICTION
• Force of friction is the force which
opposes the motion of an object over
a surface.
Example: 1) A ball rolling along the
ground gradually slows down and
finally comes to rest.
2) If we stop pedalling a bicycle, it
gradually slows down and finally
comes to a stop.
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11. MAGNETIC FORCE
• The force exerted by a
magnet is called magnetic
force.
Example: i) Force of
attraction and repulsion
between two magnets.
ii) Force exerted by a
magnet on a piece of iron or
steel
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12. ELECTROSTATIC FORCE
•The force exerted
by a charged body
on another charged
or uncharged body
is known as
electrostatic force.
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13. GRAVITATIONAL FORCE
• Objects or things fall towards the earth because it
pulls them. This force is called the force of gravity, or
just gravity. This is an attractive force. The force of
gravity acts on all objects.
• Gravity is not a property of the earth alone. In fact,
every object in the universe, whether small or large,
exerts a force on every other object. This force is
known as the gravitational force.
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15. PRESSURE
• The force acting on a
unit area of a surface
is called pressure.
• pressure = force / area
• The smaller the area,
larger the pressure on
a surface for the same
force.
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16. PRESSURE EXERTED BY LIQUIDS
AND GASES
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18. ATMOSPHERIC PRESSURE
•The envelop of air is known as the
atmosphere.
•The atmospheric air extends up to many
kilometres above the surface of the earth.
•The pressure exerted by this air is known as
atmospheric pressure.
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20. HOMEWORK
1) Define force.
2) Define pressure.
3) Write the formula of pressure.
4) Define atmospheric pressure.
5) Define contact and non contact force
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