Acceleration

Ch. 10.2

ObjectivesDescribe the concept of acceleration as a change in

velocity.

Explain why circular motion is continuous acceleration even when the speed does not change.

Calculate acceleration as the rate at which velocity changes.

Graph acceleration on a velocity-time graph.

This Graph Shows Constant Velocity1. 2.

3.

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21 22 23 24 25 26 27 28 29 30

This Graph Shows No Velocity1.

2.

3.

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21 22 23 24 25 26 27 28 29 30

What is the distance a man can run in 1 hour if he runs at 7 mi/hr?

1. 7 km

2. 7 m

3. 7 mi

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What is the Velocity of a Plane that Travels 500 mi in 1 hour

1. 500m/s

2. 500 mi/hr

3. 500 km/hr

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Using the Conservation of Momentum if car has the momentum of 50 kg*m/s and a man is in the moving car the man

has?1. 50 m/s

2. 50 kg

3. 50 kg * m/s

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AccelerationAcceleration = change in velocity divided by

the time interval in which the change occurred.

Acceleration =

a =

final velocity – initial velocity

time

vf – vi

t

UnitsAcceleration = Vf – V i

t

Units = m or m

s2 s * s

AccelerationAcceleration = rate at which velocity changes

over time Quick time movie acceleration

Acceleration occurs when there's a change in SpeedDirectionOr both change

Uniform circular motion is constant acceleration.QT Centripetal AccelerationVideo of bucket and water having centripetal

acceleration

AccelerationAcceleration can be

determined from a graph

QT Graphical Representations of Accelerations

Acceleration can also be determined from a velocity-time graph

A straight line with slope = constant acceleration

Slope of the line = acceleration

Acceleration of a Bicycle

0

5

10

15

0 1 2 3 4

Time (s)

Ve

loc

ity

(m

/s)

Horizontal line = constant speed, no acceleration or deceleration.

Constant Velocity

0

10

20

0 1 2 3 4

Time (s)

Ve

loc

ity

(m

/s)

Examine the following graph.

0

5

10

15

20

0 2 4 6 8 10

Time (s)

Velo

city

(m/s

)

A negative slope indicates that an object is slowing down or decelerating.

Negative Acceleration (Deceleration) Graph

01020

0 1 2 3 4

Time (s)

Ve

loc

ity

(m

/s)

Calculating AccelerationAcceleration is the rate at which velocity changes.

Acceleration Equation (for straight-line motion) QT Distinguishing B/W Velocity and Acceleration QT Average Acceleration

SI Units = m/s2

acceleration = final velocity – initial velocity

time a = ∆vt

The Top Thrill Dragster at Cedar Point goes from 0 m/s to 53.6 m/s (120 mph) in 4 seconds. What is its acceleration?

Given:a =Vf

=

V i =

t =

Algebra:

Substitution:

A car traveling home at a velocity of 15.6 m/s slams on its brakes and comes

to a stop to avoid a dog. If it takes 5 seconds to stop, what is the cars

acceleration?Given:a =Vf

=

V i =

t =

Algebra:

Substitution:

In what direction is the car accelerating?

How can you tell mathematically?

A Porsche Boxster has an acceleration of 4.51 m/s2. If the car starts from rest how much time would it take for the vehicle to reach a speed of 11.3 m/s? Given:

a =Vf

=

V i =

t =

Algebra:

Substitution:

A golf ball thrown from the top of the sears tower accelerates at 9.8 m/s2 toward the ground and lands on the pavement 9.2 seconds. If the

ball’s final speed is 93.0 m/s what was the speed with which the ball was initial thrown?

Given:a =Vf

=

V i =

t =

Algebra:

Substitution: