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

• Isaac Newton realized that a force acts to pull
  objects straight down toward the center of Earth.
• Gravity force that pulls objects toward each
  other.
• The acceleration due to gravity is 9.8m/s2

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Free Fall

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

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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.