distinguish between speed, velocity and acceleration

Speed, Velocity and Acceleration

In this presentation you will:

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There are lots of terms used to describe motion.

Average speed is the total distance

travelled divided by the total time

taken.

Introduction (1 of 1)

Average speed in m/s =Total distance in meters

Total time taken in seconds

After 10 minutes, car A will have traveled 10 miles. Car B will only

have traveled 9 miles.

The speed of an object is the distance it travels in a period of time.

Speed (1 of 1)

Imagine two cars passing in front of you at the same

time. Car A is traveling at a constant speed of 60 mph

(miles per hour) and car B is traveling at a lower

constant speed of 55 mph.

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Dis

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Time

Car A: 60 mph

Car B: 55 mph

Car A: 60 mph

Car B: 55 mph

The velocity of an object is its speed in a specified direction.

Velocity (1 of 1)

An object traveling at a constant speed in a

straight line is traveling with

constant velocity.

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Dis

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Time

Constant velocity is represented by a straight line on a distance-time graph.

The gradient (slope) of the line gives the object’s velocity. The steeper the line, the

greater the object’s velocity.

Displacement measures how far and in what direction an object is from its starting point.

Displacement (1 of 1)

If an object ends up at its starting point then it has

zero displacement.

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Dis

pla

cem

ent

Time

Velocity =

Displacement Time

Acceleration (1 of 2)

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This increase in velocity is known as acceleration.

Acceleration is the change in velocity

divided by the time it takes for the change

to occur.

The unit of acceleration is m/s2 (meters per second

squared). Dis

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Time

If an object traveling in a straight line increases its speed, its velocity also

increases.

Acceleration (2 of 2)

Increasing velocity is represented by an

upward curving line on a distance-time

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Dis

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Time

Acceleration occurs whenever an object’s

velocity changes.

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Dis

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Time

A decrease in velocity is a type of acceleration known as deceleration or

Negative Acceleration

Negative Acceleration (1 of 2)

Decreasing velocity is represented by a line curving to the right on a distance-

time graph.

If an object traveling in a straight line decreases

its speed, its velocity also decreases.

Negative Acceleration (2 of 2)

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If an object is traveling with constant deceleration

– its velocity is decreasing at a constant rate

– it is represented by a downward sloping

straight line.

Dis

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Time

When an object is not moving, it has a velocity of 0 m/s.

When an Object Starts Moving (1 of 2)

If the object then begins to move, its

velocity increases at the instant it moves.

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When an Object Starts Moving (2 of 2)

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When a moving object stops, its velocity drops to 0 m/s.

Acceleration occurs when the object begins to move.

Acceleration also occurs as an object is

stopping.

When the car was traveling north, its velocity was 10 m/s north. When it turned left, and was

traveling west at the same speed, its velocity changed to 10 m/s west.

Changing Direction (1 of 3)

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Velocity =

10 m/s north

Velocity =

10 m/s west

Speed = 10 m/s

Velocity is speed in a certain direction.

Velocity changes when an object

changes direction, even if it has a constant speed.

Speed = 10 m/s

Changing Direction (2 of 3)

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A car traveling north at 10 m/s turns left

and travels west at 10 m/s.

In this case, the car’s speed stays constant

at 10 m/s.Speed = 10 m/s

Velocity =

10 m/s north

Velocity =

10 m/s west

Speed = 10 m/s

Changing Direction (3 of 3)

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Acceleration occurs

- whenever velocity changes

-when an object changes direction

-When an object changes speed.

The car accelerated when it turned left.

Acceleration

Velocity =

10 m/s north

Velocity =

10 m/s west

Acceleration occurs when any object:

Acceleration (1 of 1)

starts moving

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speeds up

turns a corner

slows down

You have seen that acceleration occurs

whenever an object’s velocity

changes.

Force and Acceleration (1 of 2)

What causes an object’s velocity to

change?

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Force and Acceleration (2 of 2)An object’s velocity

changes when an unbalanced force acts

upon it.

For example, when something pushes or

pulls it.

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So, if an object’s velocity changes when an unbalanced force acts upon it, and acceleration occurs whenever an object’s velocity changes…

Newton’s law of force and acceleration states that acceleration occurs when an

unbalanced force acts upon an object

Unbalanced Forces (1 of 3)

Think of a tug of war.

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Here we have forces that are balanced.

Here we have forces that are not balanced.

There is an unbalanced force of 500 N to the right.

3000 N 3000 N

3000 N 3500 N

Owen’s two children, Luke and Lea, have challenged him to a tug of war.

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Owen can exert a pulling force of 4000 N.

Who will win the tug of war?

Lea can pull a force of 2500 N, and Luke can pull 1000 N.

Unbalanced Forces (2 of 3)

First work out the total force that Luke and Lea are exerting on the rope.

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Luke and Lea total force = 2500 N + 1000 N = 3500 N

The forces on the rope are unbalanced. The force exerted by Luke and Lea is less then the force Owen is exerting, and so Owen will win the tug of war.

Unbalanced Forces (3 of 3)

LeaOwen

Luke

4000 N 2500 N

1000 N

Difference in force = 4000 N – 3500 N = 500 N

What is the difference between speed, velocity and acceleration?

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Speed is the rate at which an object’s position changes.

Acceleration is the rate at which an object’s velocity

changes.

Speed, Velocity and Acceleration (1)

Velocity is the speed of the object in a specified direction.

Speed = Distance

Time

Acceleration =

Change in velocityTime

Question 1

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"Velocity is another word for speed.“ Is this statement true or false?

A) True. Velocity refers only to the speed of an object.

B) False. Velocity refers to the speed of an object, but also its direction.

“Displacement measures how far and in what direction an object is from its starting point.”

Is this statement True or False?

A)True

B) False

Question 2

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Which of the following can occur when an object is accelerating?

Question 3

A) The object speeds up

B) The object slows down

C) The object changes direction

D) All of the above

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A football field is about 100 m long. If it takes

Josh 20 seconds to run its length, how fast (what

speed) was he running?

A)A)20 m/s20 m/s

B)B)5 m/s5 m/s

C)C) 200 m/s200 m/s

D)D)10 m/s10 m/s

Question 4

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Question 5

What is the main difference between velocity and speed?

A. Speed is used for low speeds while velocity is used for high speeds.

B. Speed and velocity are measured in different units.

C. Speed does not have to have a direction but velocity does.

D. Speed is used to describe how vehicles move but velocity is used for all other movements.

Question 6

In which region is the runner stationary?

A) A-B

B) B-C

C) C-D

D) D-E

Question 7

Where is the runner accelerating?

A) A-B

B) B-C

C) C-D

D) D-E

Question 8

Where is the runner moving at the greatestt constant speed?

A) A-B

B) B-C

C) C-D

D) D-E

Question 9

Constant velocity is represented by a ___________ line on a distance-time graph.

A)Curved

B)Straight

C)Downward

D)Bell shaped

Question 10

Which of the following is a correct example of velocity?

A)10 m/h

B)10 West

C)10 m/h West

D)West