2.1C Acceleration

8/14/2019 2.1C Acceleration

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Acceleration = change invelocitytime

Acceleration = rate of change invelocity

a = acceleration

vf= final velocity

vi= initial

velocity

a = Vf - Vi

t


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Acceleration- has

direction, just like

velocity.

Acceleration is aVECTOR (it has both amagnitude and a direction).

The roller coaster

accelerates bothbecause its speed

changes and its

direction


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For its velocity to change, anobject must accelerate.

An object accelerateswhenever its speed

speed or

directiondirection or bothboth change.

So this means.


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An object moving in a circle at

constant speed is alwaysaccelerating (changing direction).


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How can you accelerate at a constantspeed?

Acceleration at constant speedAcceleration at constant speed

Its like gravity. An objects

velocity gets faster every second,but it gets faster at the samerate.

Objects accelerate toward theearth at a rate of 9.8 m/s2. Inother words they fall 9.8m/s

faster every second.


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O p o s i t i v e d i r e c t i o n

0 . 4 m 0 . 7 m 1 . 0 m 1 . 3 m

t = 0 s t = 1 s t = 2 s t = 3 s t = 4 s

An object is moving with uniform acceleration.

Its positions at one-second interval are shown below.

distance traveled in

the first second


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0 . 4 m 0 . 7 m 1 . 0 m 1 . 3 m

t = 0 s t = 1 s t = 2 s t = 3 s t = 4 s




thesecond second.


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0 . 4 m 0 . 7 m 1 . 0 m 1 . 3 m

t = 0 s t = 1 s t = 2 s t = 3 s t = 4 s




thethird second


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0 . 4 m 0 . 7 m 1 . 0 m 1 . 3 m

t = 0 s t = 1 s t = 2 s t = 3 s t = 4 s




thefourth second


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0 . 4 m 0 . 7 m 1 . 0 m 1 . 3 m

t = 0 s t = 1 s t = 2 s t = 3 s t = 4 s



0.4 , 0.7 , 1.0 , 1.3 is an arithmetic progression with a

common difference 0.3.

This is an important characteristic of motion with

uniform acceleration.


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ACCELERATIONAcceleration is the change in speed in an object in a period of

time.

change invelocity (m/s)

acceleration

(m/s/s)

Where do the units come from?

a = v t

a = m/s s

a = m/s/s=m/s2

It takes a cyclist 20 secondsto go from

a standing start to 14m/s.

What is their acceleration?

What is 14m/s in km/hr?

a = v/t a = 14m/s / 20s a = 0.7ms-2

= 14 60s 60min 1000m

= 50.4km/hr

v

a t

change intime (s)


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Acceleration

A cyclist accelerates from 0 to 10m/s in 5 seconds. What is heracceleration?

A ball is dropped and accelerates downwards at a rate of 10m/s2

for 12 seconds. How much will the balls velocity increase by? A car accelerates from 10 to 20m/s with an acceleration of 2m/s2.

How long did this take?

A rocket accelerates from 1,000m/s to 5,000m/s in 2 seconds.What is its acceleration?

Acceleration = change in velocity (in m/s)

(in m/s2) time taken (in s)

V

TA

SPEED/TIME GRAPHS


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SPEED/TIME GRAPHS

Time (sec)

10 20 30

Speed

(m/s)

4

8

Using the speed/time graph:

3. What distance is covered in part 1?

4. What is the total distance covered?

d = v t

d = 4m/s 10s

d = 40 m

Part 1 = 40m

Part 2 = 0m

Part 3 = 0m

Part 5 = v t = 8m/s 10 s = 80m

Part 4 = v t = 8m/s 5s = 20m

Total = 40 + 80 + 20 =140m


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ACCELERATION QUESTIONSWhat would these look like on a speed/time graph?

1. stopped

2. slow

3. fast

4. accelerating


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Velocity-time graphs

80

60

40

20

010 20 30 40 50

Velocity

m/s

T/s

1) Upwards line =

Constantacceleration

2) Horizontal line =

Constant velocity

3) Upwards line =

constant accel,slower velocity

4) Downward line =constant accel

opposite direction


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80

60

40

20

0

1) How fast was the object going after 10 seconds?

2) What is the acceleration from 20 to 30 seconds?

3) What was the deceleration from 30 to 50s?

4) How far did the object travel altogether?

10 20 30 40 50

Velocity

m/s

T/s


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Which car (red, green, or blue) experiences the greatest acceleration?

Blue car has the greatest acceleration


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Match the car to the graphMatch the car to the graph

Match the car tothe appropriategraph line.


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MORE RESOURCES

http://www.glenbrook.k12.il.us/GBSSCI/PH

http://www.fearofphysics.com/Xva/xva.html

http://www.quia.com/rr/121411.html?AP_ra http://www.physics4kids.com/files/motion_v
http://www.glenbrook.k12.il.us/GBSSCI/PHYS/CLASS/1DKin/U1L1d.htmlhttp://www.fearofphysics.com/Xva/xva.htmlhttp://www.quia.com/rr/121411.html?AP_rand=1991654762http://www.physics4kids.com/files/motion_velocity.htmlhttp://www.physics4kids.com/files/motion_velocity.htmlhttp://www.quia.com/rr/121411.html?AP_rand=1991654762http://www.fearofphysics.com/Xva/xva.htmlhttp://www.glenbrook.k12.il.us/GBSSCI/PHYS/CLASS/1DKin/U1L1d.html

2.1C Acceleration

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