Describing Motion

1
Describing Motion

• Newtons Laws

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First we need to define the word FORCE

• The cause of motion (what causes objects to move)
• Two types of forces
• Pushes
• Pulls

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Forces are measured in Newtons

• SI unit of force
• Symbol N
• Measured by using a spring scale

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Forces may be balanced or unbalanced

• Balanced forces all forces acting on an object
  are equal
• There is NO MOTION
• Unbalanced forces one or more forces acting on
  an object are stronger than others
• There is MOTION
• A NET FORCE

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Newtons Laws

• First Law Inertia
• Second Law Acceleration, Force Mass
• Third Law Action-Reaction

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First Law

• Inertia
• An object at rest not moving remains at rest
  unless acted on by a force push or pull
• An object in motion remains in motion unless
  acted on by a force push or pull

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First Law

• Inertia Mass
• Mass is the amount of matter in an object
• The more MASS an object has, the more INERTIA the
  object has.
• Bigger objects are harder to start stop

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8
Second Law

• Acceleration Mass Definitions
• Acceleration is a change in velocity speed or
  direction
• Mass is the amount of matter in an object

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Second Law

• Acceleration Force
• The more force placed on an object, the more it
  will accelerate change its motion
• Acceleration Mass
• The more mass or inertia an object has, the
  more force it takes to accelerate the object

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Third Law

• Action Reaction
• Forces are always produced in pairs with opposite
  directions equal strengths
• For every force there is an equal and opposite
  force

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The truck is in motion. What is the force that
causes it to stop? The push of the stopped
car. The car is at rest. What is the force that
causes it to move? The push of the truck.
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What about the ladder on top of the truck? The
ladder is in motion because the truck is in
motion. When the truck stops, the ladder stays in
motion. The truck is stopped by the force of the
car, but the ladder is not. What force stops the
ladder? Gravity.
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The truck is in motion, the car is at rest. How
do each of these vehicles accelerate? The truck
stops moving. The car starts moving. Which one
will be the hardest to accelerate? The truck
because it has the most mass.
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Why does the car move accelerate when it is hit
by the truck? The heavy and moving truck has more
force than the small, at rest car. Why does the
truck stop moving when it hits the car? The force
of the car pushing back on the truck, plus the
force of friction between the massive truck and
the road slow down, the stop the truck.
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The truck hits the car. An action force stops
the truck. What is the equal and opposite
reaction force? The force that pushes the car
forward.