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Motion
Definition
Event that involves a change in
the position or location of
something.
Motion is Relative
• Relative – it is described by or compared
to a REFERENCE POINT
Types of Motion
• Uniform motion - constant speed in a
straight line
• Accelerated motion – motion that is
changing in speed or direction
• Circular motion - speed is constant but the
direction of motion is changing
continuously
Forces
• Pushes or pulls
• May cause acceleration [changes in
motion]
Balanced Forces
• All forces acting on an object are equal
• There is no motion
Unbalanced Forces
• All forces acting on an object are not equal
• One or more force is stronger than others
• Motion occurs
Net Force
• The sum of all forces acting on an object
– A net force of 0
• No motion
– A net force of more than 0
• Motion occurs
Friction
• Force that slows down motion
Gravity
• Force that attracts all objects toward each
other
• More mass = more gravity
Speed
Average Speed
• Comparison of time and distance
– Distance traveled per unit time
•S=d/t
•T=d/s
•D=sxt
Speed
Instantaneous Speed
• Speed at any instant
Speed
Constant Speed
• Speed that does not change
– Instantaneous speed that does not change
Velocity
• Speed AND direction
Acceleration
• A change in velocity
– Speeding up
• Positive acceleration
– Slowing down
• Negative acceleration
• Deceleration
– Changing direction
Newton's Laws
• Describe motion and changes in motion
First Law of Motion
• Law of inertia
– Objects at rest [not moving] will not begin to
move until a force acts on them
– Objects in motion will not stop moving until a
force acts on them
– Objects with more mass have more inertia
• Bigger objects are harder to start and stop
Second Law of Motion
• Law of acceleration
– A force is needed to change motion
– Objects accelerate in the direction of the force
– The more force applied, then more
acceleration
– The more mass an object has, the more force
is needed to accelerate the object
Third Law of Motion
• Law of action-reaction
– Forces occur in pairs
– The forces are equal and opposite
– One force is an action force
– The other force is a reaction force
– The forces act on different objects