What is Velocity?What is Velocity?• VelocityVelocity refers to refers to speedspeed in a particular in a particular directiondirection• To accurately describe an object’s motion, it is To accurately describe an object’s motion, it is

necessary to give its necessary to give its speedspeed and and directiondirection• Ex: You ride your bike Ex: You ride your bike 20 km/hr east20 km/hr east• Ex: I drive my car Ex: I drive my car 95 km/hr southwest95 km/hr southwest when I go when I go

home. home. • If two velocities are headed in the same direction, If two velocities are headed in the same direction,

they can be they can be added togetheradded together. . • Ex: A train is headed Ex: A train is headed 60 M/hr East.60 M/hr East. A passenger on A passenger on

the train is walking the train is walking 3 M/hr east.3 M/hr east. The passenger’s The passenger’s total motion is total motion is 63 M/hr headed East. 63 M/hr headed East.

• If two velocities are headed in opposite directions, If two velocities are headed in opposite directions, they can be subtracted. they can be subtracted.

• Ex: A train is headed Ex: A train is headed 60 M/hr East.60 M/hr East. A passenger on A passenger on the train is walking the train is walking 3 M/hr West.3 M/hr West. The passenger’s The passenger’s total motion is total motion is 57 M/hr headed West. 57 M/hr headed West.

AccelerationAcceleration• AccelerationAcceleration is a is a

change in speed or change in speed or directiondirection

• It is simply a It is simply a change change in in velocityvelocity

• Calculate the speed Calculate the speed after 3 seconds:after 3 seconds:

• Calculate the speed Calculate the speed at 6 seconds:at 6 seconds:

• Calculate speed at 9 Calculate speed at 9 seconds:seconds:

•Notice the object’s Notice the object’s speed is increasing speed is increasing over timeover time

50 ÷ 3 = 16.6 m/sec

200 ÷ 6 = 33.3 m/sec

400 ÷ 9 = 44.4 m/sec

Analyzing GraphsAnalyzing GraphsPositive Acceleration Negative Acceleration / Deceleration

•Positive accelerationPositive acceleration is is when an object’s when an object’s speed is speed is increasingincreasing over time over time•A graph with an A graph with an upward upward slopeslope is shown is shown

•Negative accelerationNegative acceleration (deceleration)(deceleration) is when an is when an object’s speed is decreasing over object’s speed is decreasing over timetime•A graph with a A graph with a downward slopedownward slope is shownis shownAt Point At Point AA, Speed = , Speed = 83.3 m/sec83.3 m/secAt Point At Point B,B, Speed = Speed = 30 m/sec30 m/secAt point At point CC, Speed = , Speed = 7.1 m/sec7.1 m/sec

How to calculate How to calculate AccelerationAcceleration

• Acceleration = Acceleration = Final Velocity – Original Final Velocity – Original velocityvelocity Time Time

• A = A = Vf – VoVf – Vo• Time Time • If acceleration is If acceleration is increasingincreasing, it is referred , it is referred

to as to as positive accelerationpositive acceleration, , and your and your answer will be a answer will be a positivepositive number number

• If acceleration is decreasing (becoming If acceleration is decreasing (becoming negative), it is called negative), it is called decelerationdeceleration or or negative accelerationnegative acceleration, and your answer , and your answer will be a will be a negative number.negative number.

Calculating Acceleration:Calculating Acceleration:

• A rollercoaster is traveling A rollercoaster is traveling 15 meters/second15 meters/second at the top of a hill. After at the top of a hill. After 3 seconds3 seconds, it is , it is traveling traveling 30 meters/second30 meters/second when it reaches when it reaches the lower part of the hill. What is the the lower part of the hill. What is the rollercoaster's rollercoaster's acceleration?acceleration?A = Vf – Vo

Time

30 m/s – 15 m/s = 15 m/s 3 sec 3 sec

A = 5 m/s/s or 5 m/s2

Calculating Deceleration:Calculating Deceleration:

• If a car's velocity changes from If a car's velocity changes from 50 50 meters/secondmeters/second to to 20 meters / second20 meters / second in in 5 seconds5 seconds, what was the object's , what was the object's acceleration? acceleration?

A = Vf – VoTime

20 m/s – 50 m/s = -30 m/s 5 sec 5 sec

A = -6 m/s/s or -6 m/s2