Transcript 9Phys_docs\Gravity&Friction

COMPUTER PRESENTATIONS FOR
KS3 SCIENCE - PHYSICS
©2003, STEVE PARKER
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KS3 SCIENCE
- PHYSICS
Gravity, Friction
& Air Resistance
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GRAVITY
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GRAVITY
As Sir Isaac Newton
discovered, gravity is
an attraction between
any two bodies, which
depends on their mass
GRAVITY
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Because the Earth is
very massive, it pulls
objects with a force
of 10 Newtons for every
Kg of the object’s mass
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GRAVITY
Gravity pulls everything
towards the earth, so
“Projectiles” move in an arc
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FRICTION
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FRICTION
“Friction” is the stickiness between
two surfaces when they rub together,
and it is a force that opposes movement
“Static Friction” is
when two surfaces
grip as they try
to move past
each other
FRICTION
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“Friction” is the stickiness between
two surfaces when they rub together,
and it is a force that opposes movement
Without friction
you would get
nowhere when
you tried to walk
FRICTION
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“Friction” is the stickiness between
two surfaces when they rub together,
and it is a force that opposes movement
On a smooth surface
the opposing force
is not strong enough
to prevent movement
- “Sliding Friction”
FRICTION
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“Friction” is the stickiness between
two surfaces when they rub together,
and it is a force that opposes movement
Lubrication is a
slippery substance that
goes in-between two
surfaces to overcome
friction, e.g. engine oil
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AIR RESISTANCE
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AIR RESISTANCE
When an object moves through
a liquid or gas, there is friction,
which creates “Resistance”
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AIR RESISTANCE
Resistance can be reduced by
having a “Streamlined” shape
(a pointed front cuts through
the liquid or gas more easily)
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AIR RESISTANCE
Anything moving through
the atmosphere will be
affected by “Air Resistance”
AIR RESISTANCE
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Air resistance or “Drag”
is caused by air moving
around the object
Driving Force
Air Resistance
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AIR RESISTANCE
The faster the object goes,
the stronger is the air
resistance against it
Driving Force
Air Resistance
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AIR RESISTANCE
Eventually the driving force
and the air resistance are equal,
so the object stops getting faster
Driving Force
Air Resistance
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AIR RESISTANCE
There will therefore be a
maximum speed through air,
called the “Terminal Velocity”
Driving Force
Air Resistance
AIR RESISTANCE
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For a sky-diver, the terminal
velocity is around 190 km per hr
Driving Force
Air Resistance