 # Speed and Acceleration

## Presentation on theme: "Speed and Acceleration"— Presentation transcript:

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

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

Negative Acceleration
Description Graph 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

Positive Acceleration
Description Graph 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

No Acceleration Description Graph Velocity is not changing
Speed and direction are constant