Force

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Unit 2

• Force

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Force push or pull

• a force always acts in a certain direction
• ex. if you push something, the force is in the
  direction of the push

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Forces in Nature

• Electric force
• ex. lightning
• Magnetic force
• ex. magnetic poles
• Gravity

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• Weight is a force

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Newton

• metric unit of force

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What is gravity?

• Sir Isaac Newton
• 1642 1727
• The Principia

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Gravity

• force of attraction between all objects in the
  universe

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Gravity

• the larger an objects mass, the greater the
  gravitational force

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Gravity

• the greater the distance between two objects, the
  smaller the gravitational force
• the force of gravity decreases by the amount
  equal to one divided by the distance (d) squared
• 1/d2

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What is air resistance?

• air resistance
• force that opposes the movement of an object in
  air

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Air Resistance

• a larger surface area usually results in greater
  air resistance
• lighter objects feel more air resistance than
  heavier objects

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Terminal Velocity

• speed at which air resistance and gravity acting
  on an object are equal
• as an object falls, its speed increases at a
  steady rate until it reaches its terminal
  velocity

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Vacuum empty space

• in a vacuum, all objects fall at the same speed

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What is friction?

• Friction
• force that opposes the motion of an object
• the force of friction works in the opposite
  direction of the force of motion

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Types of Friction

• Sliding Friction
• the source of friction is the contact between two
  surfaces, at least one of which is in motion

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Types of Friction

• Air Resistance
• friction results from air pushing on an object as
  it is moving

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Types of Friction

• Rolling Friction
• friction between two surfaces that are not in
  constant contact
• ex. wheels

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Friction

• friction makes motion possible
• friction also makes it hard to move objects
• reducing friction makes it easier to move objects

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How can friction be reduced?

• by changing sliding friction into rolling
  friction
• by using lubricants
• Lubricants substances that reduce friction

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What is pressure?

• Pressure
• force per unit area

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Pressure

• pressure is the amount of force acting on a
  surface
• pressure equals force divided by area
• p f/a

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Pressure

• pressure can be changed by changing the amount of
  force acting on an area
• pressure can be changed by changing the area on
  which a force acts

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Fluid Pressure

• pressure in gases and liquids

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Air Pressure

• air pressure is caused by the motion of particles
  in the air
• you do not feel the weight of the air because the
  pressure inside your body is equal to the air
  pressure around you

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Air Pressure

• air pressure changes with altitude
• the higher you are, the lower the air pressure

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Air Pressure

• Barometer
• instrument used to measure air pressure

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Water Pressure

• the force of water pressure on an object is the
  same in all directions
• water pressure changes with depth
• the deeper you are, the greater the water pressure

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Water Pressure

• Manometer
• instrument used to measure pressure in a liquid

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What is Bernoullis principle?

• Bernoullis Principle
• principle that states that as the speed of a
  fluid increases, its pressure decreases

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Bernoullis Principle

• airplane wings are designed to use Bernoullis
  principle
• air traveling over the wings moves faster than
  air underneath
• this reduces the pressure on top of the wing,
  allowing it to be pushed upward

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Bernoullis Principle

• three forces combine to help an airplane fly
• the upward force on a planes wing is called lift
• a forward force, or thrust, helps the plane take
  off and maintain air speed
• the air resistance on a plane is called drag