FRICTION

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FRICTION
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What is FRICTION?

• When you push your book on your desk, the 2
  surfaces rub together.
• The force that one surface exerts on another when
  the two rub against each other is called
  FRICTION.
• 3 types (sliding, rolling, fluid)

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• Friction acts in the direction OPPOSITE to the
  direction of the objects motion

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What affects friction?

• The strength of the force of friction depends on
  2 factors the types of surfaces involved and how
  hard the surfaces push together.
• Example Rough surfaces produce more friction

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Is Friction useful or not?

• Go to the following website, list 2 situations in
  which friction is usefuland 2 in which it is not
  useful
• Dirtmeister Friction -- Investigate the Facts

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FRICTION.

• Now I want you to go to the following website.
  FearOfPhysics.com What is Friction? Read the
  web page and explain in your own words what the
  drawing is showing you.
• After you have explained what it is showing you,
  click on the bottom of the screen where it says
  Click here to do an experiment with friction .
  show Mrs. Allen when you have successfully
  completed the friction activity (try at least
  three different scenarios 15 points).

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Bar Graph/Frictional Surfaces
Which surface has the causes the most friction?
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Gravity

• Gravity is the force that pulls all objects to
  Earth

• Gravity accelerates all objects to Earth
• at 9.8 m/s2in other words acceleration
• due to gravity is 9.8 m/s2 .

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Gravity keeps the moon in orbit with the Earth
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Free Fall
In fact, all objects will fall at 9.8m/s2 if the
air does not act to slow them down.  An easy
proof of this is to drop a grape and a grapefruit
at the same time from the same height. 
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AIR RESISTANCE

• A type of fluid friction
• Greater the surface area the greater the air
  resistance

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AIR RESISTANCE
However, if you drop a book and a piece of paper,
you will notice that the paper does not
accelerate as much as the book because the small
force of gravity on the paper is easily opposed
by the force of air friction on the paper.  A
similar force acts on the book from the air but
it is small compared to the force of gravity on
it. 
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PROJECTILE MOTION

• Objects thrown in a horizontal direction will hit
  the ground at the same time as one dropped
  straight down.

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Projectile Motion
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WEIGHT

• Measure of the force of gravity on an object
• Formula
• Weight mass X acceleration due to gravity

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Weight
Go to the following website http//www.explorato
rium.edu/ronh/weight/ What is your weight on
other planets? Write down four.