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.

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------50 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---- 25m

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• 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