Friction, Gravity, and Pressure

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Friction, Gravity, and Pressure
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Friction

• Friction - The force that one surface exerts on
  another when the two rub against each other.
• Acts in a direction opposite to the objects
  direction of motion.
• Opposes motion, eventually will cause object to
  stop.
• Strength depends on 2 factors type of surface
  and how hard the surfaces push together.

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Types of Friction

1. Sliding solid surfaces slide over each other.
   (more force needed to overcome than rolling)
2. Rolling object rolls over a surface. (Less
   force needed than sliding)
3. Fluid occurs when an object moves through a
   fluid. (less force needed to overcome than
   sliding) Fluid keeps surfaces from making direct
   contact reduces friction.

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Gravity

• Force acts to pull objects straight down toward
  the center of Earth
• Gravity force that pulls objects toward each
  other.

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Free Fall

• Free Fall when the only force acting on a
  falling object is gravity.
• In free fall unbalanced force
• Near surface of earth force of gravity is 9.8
  m/s2 every sec increases by 9.8.
• All objects in free fall accelerate at the same
  pace regardless of mass
• Projectile object is thrown

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Air Resistance

• All objects are supposed to fall at same rate,
  not always the case.
• Air resistance objects falling though air
  experience type of fluid friction.
• Not the same for all objects
• Air resistance increases with velocity,
  eventually equals force of gravity and is
  balanced no acceleration
• Terminal velocity- the greatest velocity an
  object reaches

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Growth of Seedlings

• Plants grow vertically response to gravity
  Gravitropism
• Stem grows up (opposite of gravity), roots grow
  down (direction of gravity)

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Weight

• Weight - measure of the force of gravity on an
  object.
• Mass amount of matter in an object.
• Weight measured in Newtons

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Newtons Third Law

• For every action there is an equal and opposite
  reaction
• States that if one object exerts a force on
  another object, then the second object exerts a
  force of equal strength in the opposite direction
  on the first object.

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Pressure

• Equal to the force exerted on a surface divided
  by the total area over which the force is
  exerted.
• Force and pressure closely related by not the
  same.
• Calculate Pressure Pressureforce/area
• Measured as pascal

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Pressure in a Volcano

• Volcano is in equilibrium as long as the force
  exerted by the built-up fluid is not greater than
  the rocks strength.
• Fluid in volcano exerts a pressure (force)
  causes it to explode.

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Force Pumps and Blood Flow

• Heart is a force pump
• Blood fluid in heart, pumped through circulatory
  system by heart
• When force is applied to a confined fluid, an
  increase in pressure is transmitted equally to
  all parts of the fluid Pascals Principle
  (explains how heart pumps blood through body)