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...
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Speed & VelocityHow fast How far is changing.
The rate at which an object moves.
distance
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VelocityVelocity is a vector. It has both magnitude (speed) and direction.
Instantaneous velocity is the velocity at any instant.
distance
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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
= =
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Speed QuestionA motorcycle travels 1000 m in 2 minutes.
What is its average speed?
total distance traveledAverage Speed = total time
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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?
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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
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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?
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Acceleration and velocity do not have to be in the same direction.
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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.
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Hill Question
On which of these hills does the ball roll down with increasing speed and decreasing acceleration? a) b) c)
a) b) c)
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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?
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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=
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Free FallIn a vacuum, all objects fall with the same
acceleration due to gravity: 10 m/s2.
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Free Fall Speed
25d t=
210 /a g m s= =
10v t=
Do Work Book
v at=
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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
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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?
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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.