# Speed & Velocity - Santa Rosa Junior Collegelwillia2/p10_f08/p10ch3p2.pdf · Speed & Velocity How...

### Transcript of Speed & Velocity - Santa Rosa Junior Collegelwillia2/p10_f08/p10ch3p2.pdf · Speed & Velocity How...

Speed & VelocityHow fast How far is changing.

The rate at which an object moves.

distance

VelocityVelocity is a vector. It has both magnitude (speed) and direction.

Instantaneous velocity is the velocity at any instant.

distance

total distance traveledAverage Speed = total time

dt

Δ=Δ

•Speed: Scalar (magnitude)•Velocity: Vector (magnitude AND direction)•Unit is m/s• s and v often interchanged …..

Speed & Velocity

[ ] [ ]speed , distancem ms

= =

Speed QuestionA motorcycle travels 1000 m in 2 minutes.

What is its average speed?

total distance traveledAverage Speed = total time

Distance

averaged v t=

total distance traveledAverage Speed = total time

Average Speed x total time= total distance traveled

If you travel an average of 80 km/hr for 15 minutes, how far have you traveled in that time?

AccelerationHow fast How fast is changing.

The rate at which the speed is changing.

Speeding up

Slowing down

Speeding up or slowing down?

change in velocitychange in time

vat

Δ= =

Δ

Velocity from Acceleration

change in velocitychange in time

vat

Δ= =

Δ

v a tΔ = Δ

v at=

If you start from rest and accelerate at a rate of 5m/s every second (5 m/s2) for 10 seconds, what will be your final speed?

Acceleration and velocity do not have to be in the same direction.

Motion Question

Can an object move if the net forces acting on it are zero? Give an example.

Can an object be stationary but still be accelerating?Give an example.

Hill Question

On which of these hills does the ball roll down with increasing speed and decreasing acceleration? a) b) c)

a) b) c)

Tracks QuestionTwo balls are released simultaneously from rest at the left end of equal length tracks A and B as shown. Which ball reaches the end of its track first?

Free FallIn the absence of air resistance,all objects fall due to the force of gravity with an acceleration “g”:

2 29.8 / ~ 10 /g m s m s=

Free FallIn a vacuum, all objects fall with the same

acceleration due to gravity: 10 m/s2.

Free Fall Speed

25d t=

210 /a g m s= =

10v t=

Do Work Book

v at=

Free Fall: Throwing UPWhat is the speed at the top of the path?(assume g = 10m/s2 )

ZERO!

What is the acceleration at the top?

g=10m/s2

What is the speed at the same height on the way down?

-30 m/s

+y

Free Fall Symmetry

SAME!The gravitational field is symmetric

(in the absence of air resistance.)

Which ball has the greatest speed when it hits the ground?

Free Fall Summary

25d t=

For an object without an initial velocity and without air resistance.

210 /a g m s= =

10v t=

If there is an initial velocity, then add it!

( ) 10iv t v t= + 2( ) 5id t v t t= +Do Aunt Minnie problems in the Practice Book.