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Force & Motion

If I have ever made any valuable discoveries, it has been due more to patient attention, than to any other talent

Isaac Newton

Speed & Velocity

• Speed involves distance & time
  • Average speed - can be calculated by dividing total distance by total time.

  S= D/T

  • Instantaneous speed - an object's speed at a specific moment
  • When instantaneous speed does not change , an object is moving at constant speed ; in this situation average speed and instantaneous speed are the same .
  • Speed can be represented on graphs:

• Speed and direction of motion is velocity .
• Acceleration is the change in velocity divided by the time it takes for the change to happen. It can be a change in speed or a change in direction or both .
  • Acceleration can be calculated using this formula:

a = ( final speed - initial speed ) / Time

Acceleration can be shown on graphs.

 

• Acceleration may be positive or negative . Negative acceleration is sometimes called deceleration .

 

Forces

• Force - a push or pull
  • A force is a push or pull
  • The ability to change an object's motion
  • Starting
  • Stopping
  • Speeding up
  • Slowing down
  • Changing direction
  • May change an object's shape
  • Forces give energy to an object
  • All of the forces acting on an object together are known as net forces
  • Balanced forces are equal forces
  • No movement or change in movement occurs
  • Unbalanced forces are unequal forces
  • Some change in movement occurs
  • Gravity is a force that pulls objects toward each other
  • Friction is a force that slows down motion
  • Forces can be represented with arrows called vectors .
  • Vectors show the direction and magnitude of a force .
  • Forces are measured in newtons ( n ).

• Forces can be described with Newton's Laws of Motion
• First Law - Law of Inertia
  • Newton 's 1 st law - The Law of Inertia
    • A moving object moves in a straight line with constant speed unless a force acts on it.
    • The tendency of an object at rest to remain at rest and an object in motin to remain in motin unless acted upon by an unbalanced force.
  This is known as INERTIA .
  • An object's tendency to resist a change in motion is inertia .
  • The more mass an object has, the more inertia it has.
    • This means that the more mass an object has, the harder it is to move, stop, or change the speed or direction of the object.
    • An object will not start moving unless a force acts on it
    • An object will not stop moving unless a force acts on it
    • An object will not change speed unless a force acts on it
    • An object will not change direction unless a force acts on it
  • Inertia is the tendency of an object to not change it's motion
    • If it is moving, it keeps moving in the same direction
    • If it is at rest, it stays at rest
  • Objects do not change their motion unless a force acts on them

   

• Second Law - Law of Acceleration
• Mass, force and acceleration are related
• If an object is acted upon by a net force, the change in velocity will be in the direction of the force.
• Objects move in the direction they are pushed or pulled .
• Acceleration can be calculated as

Acceleration = force/mass

~or~

Force = mass X acceleration (F=ma)

• The more mass an object has the more force it takes to cause acceleration.
• Big masses are hard to accelerate.
• Small masses are easy to accelerate.
• Objects accelerate more quickly when a greater force is used.
• The more mass an object has, the more force is need to accelerate the object
• The more that is applied to an object, the more it will accelerate
• Third Law - Law of Equal and Opposite Forces
• Action-reaction
• Forces act in pairs
  The forces are equal and opposite
  • When one object exerts a force on another object, the second object exerts a force of equal strength in the opposite direction on the first object
  The first force is the action force.
  • The second force is the reaction force.
  • The equal and opposite forces act on different objects .