ACCELERATION: C10,S2

1

ACCLELERATION DEFINITION

the rate at which velocity changes

(includes: speeding up, slowing down, or

changing directions)2

Speeding up; also called accelerating

POSITIVE ACCELERATION

3

Slowing down; also called deccelerating

NEGATIVE ACCELERATION

4

Turning, which is a change of direction, is also acceleration

CHANGE of DIRECTION

5

•Acceleration is always caused by a force (a push or a pull on something).

FORCE of ACCELERATION

• For example:A)What force causes a bicycle to stop?o Friction caused by brakes pushing on

tireso Friction caused by tires pushing on road

6

FORCE of ACCELERATION,

continued…B) What force causes a car to turn?

- Friction pushing against the side of the tires.

7

FORCE of ACCELERATION,

continued…C) What force causes a rocket to take off?- The force of the exhaust gases pushing out the bottom of the rocket.

8

FORMULA of ACCELERATION

SI Units of ACCELERATION

m/s/s or m/s2

or even… km/h/s ** This is because you are

dividing speed (m/s or km/h) by time (s)

10

EXAMPLE - #1

SOLVE FOR ACCELERATION:

0 km/hr

5 km/hr 10 km/hr 15 km/hr 20 km/hr25 km/hr

0 sec 1 sec

2 sec 3 sec 4 sec 5 sec

11

The acceleration of a motorcycle is 5 km/hr/sec (every second, the motorcycle will increase its speed by 5 km/hr)

EXAMPLE #2A man jumps from a plane. His beginning speed is 100 km/hr SE (southeast), and his final speed with his parachute is 10 km/hr SE (southeast). This took 3 sec. What was his acceleration?

The negative sign means that he was decelerating (slowing down).12

a = Sf – Ss t

a = ? Sf= 10km/hr

Ss= 100km/hr t = 3s a = (10 km/hr – 100 km/hr)

3s= -90km/hr

3s= -30km/hr/s

SOLVE FOR ACCELERATION:

ACCELERATION REVIEW #1

1) A change in velocity (or speed) divided by the time it takes for the change to occur equals the object’s _______.

13

ACCELERATION REVIEW #2

2) Imagine yourself driving a car down an empty stretch of road. Describe 3 ways you could you change your acceleration.

14

3) Calculate the acceleration of a bus whose speed changes from 6m/s to 12m/s over a period of 3s.

ACCELERATION REVIEW #3

15

ANSWER:

1) The answer is acceleration. Remember that, like velocity, acceleration has a direction. A car that takes a turn has changed its acceleration, even if nothing else changes.

ACCELERATION REVIEW #1

16

ANSWER:

2) You could step on the gas; you could also step on the brake; you could turn the wheel, or do any combination of these.

ACCELERATION REVIEW #2

17

ANSWER: Calculate the acceleration of a bus whose speed changes from 6m/s to 12m/s over a period of 3s.

ACCELERATION REVIEW #3

18

a = Sf – Ss t

a = ? Sf= 12m/s

Ss= 6m/s t = 3s a = (12 m/s – 6 m/s)

3s= 6m/s

3s= 2 m/s/s

PART 2Interpreting

Graphs19

• You can represent the acceleration of an object with a speed-time graph

• speed is plotted on the vertical axis (y)

• time is plotted on the horizontal axis (x)

Reading Graphs of Acceleration

• An object that is speeding up will have a line that slopes upward (Ex. A)

Reading Graphs of Acceleration

• An object that is slowing down will have a line that slopes downward (Ex. C)

Reading Graphs of Acceleration

• A horizontal line represents an acceleration of zero or constant speed (Ex. B)

Reading Graphs of Acceleration

Copy Graph Below and Label

25

ACCELERATION REVIEW #4

4) When reading an acceleration graph, what variable will you find on the y-axis? On the x-axis?

HINT: a = Sf – Ss t

26

ANSWER #4

SPEED (y-axis)&

TIME (x-axis)

a = Sf – Ss t

ACCELERATION REVIEW #55) What is happening at point A in this speed-time graph? A. the object is speeding upB. the object is slowing downC. the object is at restD. the object has a constant speed

27

Point A = object is speeding

up

LABEL THIS ON YOUR GRAPH

ANSWER #5

28

ACCELERATION REVIEW #6

29

6) What is happening at point B in this speed-time graph? A. the object is speeding upB. the object is slowing downC. the object is at restD. the object has a constant speed

ANSWER #6

30

Point B = object has a

constant speed

LABEL THIS ON YOUR GRAPH

ACCELERATION REVIEW #7

31

7) What is happening at point C in this speed-time graph? A. the object is speeding upB. the object is slowing downC. the object is at restD. the object has a constant speed

ANSWER #7

32

Point C = object is slowing down

LABEL THIS ON YOUR GRAPH