Transcript Science of VIII Force and Pressure

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Force & Pressure
By
Nitin Oke
For Safe Hands Akola
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Force
• Force is needed to move a stationary object or to
stop a moving object or to change the direction
of moving object or to change the speed of
object. In short to bring change in state of motion
of object
• Force is also needed to change the shape of
object.
• Force may be contact force or non contact force
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Types of Force
• Force may be contact force or non contact force.
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An object is taken up
Playing tug of war
Attracting iron piece by magnet
Object falling down
Weight lifter lifts the weight
An archer pulls the bow
Light glow due to electricity
Kite fly in sky
• Force may be push force or pull force.
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Information about force
• Force is vector quantity
• Unit of force is newton (N) or dyne or kg m/s2
• The concept of force was developed by
Newton
• Gravitation, Muscular, Electrical, magnetic,
friction, normal reaction, tension, nuclear are
examples of force
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Effect of force
• Pressure: (Amount of )Force applied ( in
perpendicular direction ) on unit area is called
as pressure.
– Unit of pressure is N/m2 or pascal ( Pa)
• To increase pressure (for same force) we need
to decrease the area
– Knife has sharp edge
– Nail has pin point
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Effect of force
• To decrease the pressure ( for same force) we
need to increase area
– Broad belts of school bags
– Wide grips of handle
– Porter using roll of cloth before placing a load on it
• If pressure is same then larger the area
greater the force and smaller the area smaller
the force.
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Pressure due to liquid or gas
• When we enclose the liquid or gas in a
container it exerts pressure on walls of
container.
– The pressure due to liquid is because of its weight
of column and is same in all directions.
– The pressure due to gas is because of its randomly
moving “particles” hit the container of gas.
• Equal pressure is exerted in all possible
directions
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Effects due to pressure
• When liquid is enclosed in a tube (channel) it
flows from end of high pressure to end of low
pressure.
– Flow of blood is due to pressure of heart
– Drink rises through straw due to lung pressure
– Tooth pest come out when we squeeze it to
increase the pressure
– Injection injects due to pressure.
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Atmospheric pressure
• Our surrounding is made up of gases like
nitrogen 78% , oxygen 21% , carbon dioxide &
Argon (0.98%) , remaining water vapor. Its
weight creates force and hence pressure
called as atmospheric pressure.
• It is 1.031 x 105N/m2
• nearly 105N per sq meter.
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Use of atmospheric pressure
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It holds our body, to burst
It changes air, to wind hence rains
It allows us to use straw to drink.
Takes away the air from inflated balloon when
we lose the grip.
• It was responsible factor for experiment
performed by Otto Van Guericke which was
witnessed by great Napoleon Bonaparte.
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Magnetism
By
Nitin Oke
For Safe Hands Akola
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