Bellringer 9.4.14

1. How is velocity different from speed?

2. Which two factors (variables) determine an object’s velocity?

3. Guess which graph below shows a constant velocity A or B?

Instantaneous SpeedInstantaneous Speed

Speed can be Speed can be measured at a measured at a certain point in certain point in timetime. .

For instance, if For instance, if you are driving, you are driving, your speedometer your speedometer may read 30 may read 30 mi/hr.mi/hr.

You don’t have to drive You don’t have to drive for an hour for your car for an hour for your car to know this – your to know this – your speed is instantaneous.speed is instantaneous.

Velocity (Speed)Velocity (Speed)

Speed is a rate for the distance traveled per unit of time

Velocity is speed in a direction

Velocity = Velocity = DistanceDistance TimeTime

Measured in m/s (meters per second)Measured in m/s (meters per second)

V

d

t

Calculating VelocityCalculating Velocity

1.1. After driving for exactly 60 seconds, you After driving for exactly 60 seconds, you have driven 600 meters. What velocity have driven 600 meters. What velocity were you driving?were you driving?

V= d/tV= d/t d=600m t= 60s v= 600md=600m t= 60s v= 600m60s60s

v= 10 m/sv= 10 m/s

2.2. You know you can drive You know you can drive 80 km/hr to get to the concert. The 80 km/hr to get to the concert. The

concert is 470 km away. How concert is 470 km away. How long will it take for you to get long will it take for you to get there?there?

V= d/tV= d/t t= ? v=80 km/hr d=470 t= ? v=80 km/hr d=470

80=470/t t=470/8080=470/t t=470/80

t= 5.88 t= 5.88 hrshrs

Calculating Velocity / Time / Dist.Calculating Velocity / Time / Dist.

Constant VelocityConstant Velocity

Constant Velocity - means an object does Constant Velocity - means an object does not speed up or slow downnot speed up or slow down..

Which car is moving fastest? Which is Which car is moving fastest? Which is moving at a constant speed?moving at a constant speed?

Graphing Constant SpeedGraphing Constant Speed

How to read a Constant Velocity Graph

Motion Maps

Pretend you are eating a dripping ice cream cone while you are walking

What kind of motion do the drips mean?

a). . . . . . .

b). . . .

AccelerationAcceleration

Acceleration Acceleration occurs when an occurs when an object:object:

1.1. Speeds upSpeeds up

2.2. Slows downSlows down

3.3. **Changes **Changes direction**direction**

AccelerationAcceleration

Acceleration is Acceleration is the rate of change of the rate of change of velocityvelocity

Graphing Changing SpeedGraphing Changing Speed

Graphing Changing SpeedGraphing Changing Speed

AccelerationAcceleration

Acceleration is found by:Acceleration is found by:

a = a = (v(vff – v – vii))

timetime

The units are m/sThe units are m/s22

Calculating AccelerationCalculating Acceleration

1.1. A car goes from 0 m/s to 20 m/s in 6 s. A car goes from 0 m/s to 20 m/s in 6 s. What is the car’s acceleration?What is the car’s acceleration?

Vf= 20m/sVf= 20m/s

Vi = 0m/sVi = 0m/s

T=6sT=6s

a = vf-vi t

a= 20-0 = 3.33m/s² 6

Calculating AccelerationCalculating Acceleration

2. A man was running at 3 m/s. In 4 2. A man was running at 3 m/s. In 4 seconds, he slowed down so his velocity seconds, he slowed down so his velocity is now 1 m/s. What was his is now 1 m/s. What was his acceleration?acceleration?

Vf= 1m/sVf= 1m/s

Vi = 3m/sVi = 3m/s

T= 4sT= 4s

a = vf-vi t

a= 1-3m/s = -0.5m/s² 4s

Finding Unknowns with Finding Unknowns with AccelerationAcceleration

3. A bobcat starts running at 30m/s and his 3. A bobcat starts running at 30m/s and his acceleration is 5m/s/s. What would his final acceleration is 5m/s/s. What would his final velocity be if he ran for 5 seconds?velocity be if he ran for 5 seconds?

Vf= ?Vf= ?

Vi = 30m/sVi = 30m/s

T= 5sT= 5s

a= 5m/s²a= 5m/s²

a = vf-vi t

5m/s² m/s² = Vf—30m/s 5s

25=vf-30 55=vf

A girl is riding her skateboard to the park, and she started out going 5m/s but by the time she got down the hill, she was going 22m/s. If her acceleration was 3m/s², how long did ², how long did she ride the skateboard?she ride the skateboard?