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Forces.

  • a force is a push or pull.

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  • measured in Newtons

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  • symbolized with arrows to show their strength and direction.

2 N

10 N

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Balanced Forces

  • Balanced forces don’t change motion
    • Cancel each other out

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50 N left

50 N right

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Unbalanced Forces

  • Forces that don’t have the same strength don’t cancel each other out, and change motion
    • Objects accelerate in direction of stronger force

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100 N left

50 N right

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Thought questions.

1. What happens when forces are balanced?

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2. What happens when forces are unbalanced?

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Gravity

  • Reason why things fall to the ground
      • Gravity acts even when the objects don’t touch

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  • Pulls objects downward

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Gravity

The force of gravity is the force with which the Earth, Moon, or other massively large object attracts another object towards itself. By definition, this is the weight of the object.

All objects on Earth experience a force of gravity that is directed "downward" towards the center of the earth.

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Friction

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  • Friction
    • A force that acts in the opposite direction of the motion of the object (slows object down)

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Friction

  • Can also affect objects that aren’t moving
    • Object sitting on an incline and not sliding

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  • Different materials provide different amounts of friction!

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-Friction-

A box slides across ice and a wooden floor.

Which one will come to a stop first? Explain.

ice

wood floor

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Air Resistance

  • Interaction between a moving object and air molecules
    • Type of friction
  • Size, shape of object and speed affect
    • Larger objects
    • Faster moving objects
      • More air resistance

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  • MASS = the amount of matter in an object
  • WEIGHT = the force of gravity acting on an object, will change if the force of gravity changes (ex. Walking on the moon).

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Weight

  • WEIGHT IS NOT THE SAME AS MASS!!!!!
      • Amount of matter something has
    • Measure of the force of gravity on an object
  • Weight is a force

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  • What is the difference between weight and mass?

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Practice

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  • How much does a boy with a mass of 55 kg weigh?
  • When and how would his weight change?

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