MotionMotion

Definition

Event that involves a change in the position or location of

something.

Motion is Relative

• Relative – it is described 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

Scalar Quantities

• Show magnitude [amount] only– Speed, time, temperature

Vector Quantities

• Show magnitude and direction– Velocity, acceleration, force

• May be graphically represented– Arrows

SpeedAverage Speed

• Comparison of time and distance– A scalar quantity [magnitude only]– Distance traveled per unit time

• S = d / tS = d / t

• T = d / sT = d / s

• D = s x tD = s x t

SpeedInstantaneous Speed

• Speed at any instant

SpeedConstant Speed

• Speed that does not change– Instantaneous speed that does not change

Velocity

• Speed AND direction– A vector quantity [magnitude & direction]

Acceleration

• A change in velocity– Speeding up

• Positive acceleration

– Slowing down• Negative acceleration• Deceleration

– Changing direction

Forces

• Pushes or pulls

• May cause acceleration [changes in motion]

• May also cause changes in shape

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

Resultant

• Another term for net force

Friction

• Force that slows down motion– Air resistance creates friction in most

situations

Gravity

• Force that attracts all objects toward each other

• More mass = more gravity

• Acceleration because of gravity is 9.8 m/s/s

• All objects accelerate at the same rate

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