SPEED AND ACCELERATION

MOTION  Motion occurs when an object changes position relative to a reference point  You do not need to see an object in motion in order to know that movement has taken place

TIME  A particular moment  Interval of time  Measured in years, days, hours, minutes, and seconds  Remember – science measures in seconds  Always a number and a unit s

DISTANCE  How far from one point to another  Unit of length  English and metric  Remember – metric only in science  Always a number and a unit m

DISPLACEMENT  Displacement is the distance and direction of an object's change in position from the starting point  Displacement is different than distance if an object changes direction during its motion

SPEED  Speed is the distance an object travels per unit of time.  Measure of how quickly an object moves from one place to another  An object that is not moving still has a speed--- zero (0 m/s)  S = d t

SPEED  s = d t  s = speed  d = distance  t = time

AVERAGE SPEED  Total distance traveled total time traveling  Speed does not have to be constant  90m/30 min = 30 m/m  90m/90min = 1 m/m

INSTANTANEOUS SPEED  Speed at a certain moment in time  A speedometer shows how fast a car is going at one point in time or at one instant.

CHANGING INSTANTANEOUS SPEED  When something is speeding up or slowing down, its instantaneous speed is changing.  If an object is moving with constant speed, the instantaneous speed doesn't change

CHANGING SPEED  Speed is usually not constant  Picture riding a bike or going out for a walk

VELOCITY  Velocity is speed of an object plus its direction  EX - a car is traveling 65 mi/hr north  Velocity = v  Therefore v = d t

VELOCITY  Velocity depends on direction as well as speed so the velocity of an object can change even if the speed of the object remains constant  The speed of this car might be constant, but its velocity is not because the direction of the car is always changing.

GRAPHING SPEED  A speed graph is always position vs time  Position (or distance) is on the y axis  Time is on the x axis  The slope of a position time graph is speed

A D C B Calculate the average speed at each point: A._________ B._________ C._________ D._________ Did the car accelerate or stay at a constant speed?

The following graph shows the distance Kim traveled on her bicycle trip and the amount of time it took her to travel that distance. The following graph shows the distance Kim traveled on her bicycle trip and the amount of time it took her to travel that distance. During which 5- minute interval did Kim achieve the greatest average speed? What may have happened between t = 10 and t = 15 minutes?

WHAT IS THE SPEED?

ACCELERATION Section 2.2

ACCELERATION, SPEED AND VELOCITY  Acceleration is the rate of change in velocity  When the speed OR direction of an object changes, the object is accelerating  Acceleration can be positive or negative  If an object is slowing down, it is negative  If an object is speeding up, it is positive

CHANGING DIRECTION  An object’s speed does not have to change for it to accelerate  An object is accelerating if it’s direction changes as well

CALCULATING ACCELERATION  A= Vf –Vi/t  Acceleration equals final velocity-initial velocity divided by time  Vf-Vi is also called change in velocity  Units are speed over time  m/s/s or m/s 2

NEGATIVE ACCELERATION DESCRIPTION  Happens when an object slows down  Final velocity is less than the initial  Example: A car brakes from 30 mph to a stop  Change in speed= 0mph- 30mph = -30 mph GRAPH

POSITIVE ACCELERATION DESCRIPTION  Happens when an object speeds up  Final velocity is more than the initial  Example: A car accelerates from 0 mph to 60 mph  Change in speed= 60 mph- 0mph= 60 mph GRAPH

NO ACCELERATION DESCRIPTION  Velocity is not changing  Speed and direction are constant GRAPH