Chapter 13- The forces of Nature

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Chapter 13- The forces of Nature

• 8th grade Science

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I. What is Force?

• A. Isaac Newton- is considered the founder of
  modern physics and is one of the greatest names
  in the history of human thought.
• B. Force- is any push or pull.
• E.g.- jet engine, magnet, door closing.
• A force gives energy to an object, sometimes
  causes it to start moving, stop moving, or change
  directions.

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II. Combining Forces

• When two forces are acting in the same direction,
  they are added together.
• E.g.- You and a friend try to push a wagon full
  of rocks
• When the total force of an object is in one
  direction, the force is called unbalanced.
• An unbalanced force changes the motion of an
  object.

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• C. When two forces act in opposite directions,
  the combine by subtraction. If one force is
  greater than the other, the object would move in
  the direction of the greater force. (e.g.
  tug-of-war)
• D. If the two forces are equal the object would
  remain stationary. There would be no force acting
  on the object.
• E. Forces that are in opposite directions and are
  equal in size are called Balanced Forces. When
  forces are balanced, there is no change in motion.

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III. Friction

• When two surfaces are touching, a force called
  Friction exists.
• Friction will cause a moving object to slow down
  and finally stop.
• Friction is a force that acts in the opposite
  direction to the motion of a moving object.
• Friction occurs from the fact that objects and
  surfaces are not perfectly smooth.

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• C. Friction is dependent upon how hard the
  surfaces are forced together and on the materials
  of which the surfaces are made.
• D. The force you apply to an object must be
  greater than that force in order to move the
  object.
• E. Sliding Friction- when solid objects slide
  over each other.

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• F. Rolling Friction- is produced by objects such
  as wheels or ball bearings.
• This type of friction tends to be less than
  sliding friction.
• E.g.- Imagine cars without wheels, rolling vs.
  sliding.
• G. Fluid Friction- the force exerted by a fluid.
  Fluid friction is less than sliding friction.
• Lubricants are used to change friction to fluid
  friction, reducing friction.
• Lubricant is a slippery substance such as grease.
  
• H. Friction can be helpful in certain activities.
  E.g.- walking and driving.

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IV. Newtons Laws of Motion

1. In 1665 and 1666, Isaac Newton developed three
   laws that describe motion, -rest, -constant
   motion, -accelerated motion.
2. Newtons First Law-