Speed Velocity and Acceleration

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Speed, Velocity and Acceleration
In this presentation you will

• distinguish between speed, velocity and
  acceleration

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Introduction (1 of 1)
There are lots of terms used to describe motion.
Average speed is the total distance travelled
divided by the total time taken.
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Speed (1 of 1)
The speed of an object is the distance it travels
in a period of time.
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.
Car A 60 mph
Distance
Car B 55 mph
Time
After 10 minutes, car A will have traveled 10
miles. Car B will only have traveled 9 miles.
Car A 60 mph
Car B 55 mph
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Velocity (1 of 1)
The velocity of an object is its speed in a
specified direction.
An object traveling at a constant speed in a
straight line is traveling with constant velocity.
Distance
Time
Constant velocity is represented by a straight
line on a distance-time graph.
The gradient (slope) of the line gives the
objects velocity. The steeper the line, the
greater the objects velocity.
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Displacement (1 of 1)
Displacement measures how far and in what
direction an object is from its starting point.
If an object ends up at its starting point then
it has zero displacement.
Displacement
Time
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Acceleration (1 of 2)
This increase in velocity is known as
acceleration.
The unit of acceleration is m/s2 (meters per
second squared).
Distance
Acceleration is the change in velocity divided by
the time it takes for the change to occur.
Time
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Acceleration (2 of 2)
If an object traveling in a straight line
increases its speed, its velocity also increases.
Acceleration occurs whenever an objects velocity
changes.
Distance
Increasing velocity is represented by an upward
curving line on a distance-time graph.
Time
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Negative Acceleration (1 of 2)
A decrease in velocity is a type of acceleration
known as deceleration or Negative Acceleration
Distance
Time
Decreasing velocity is represented by a line
curving to the right on a distance-time graph.
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Negative Acceleration (2 of 2)
If an object traveling in a straight line
decreases its speed, its velocity also decreases.
Distance
Time
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.
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When an Object Starts Moving (1 of 2)
When an object is not moving, it has a velocity
of 0 m/s.
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)
Acceleration occurs when the object begins to
move.
When a moving object stops, its velocity drops to
0 m/s.
Acceleration also occurs as an object is stopping.
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Changing Direction (1 of 3)
Velocity is speed in a certain direction.
Velocity 10 m/s west
Speed 10 m/s
Velocity changes when an object changes
direction, even if it has a constant speed.
Velocity 10 m/s north
Speed 10 m/s
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.
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Changing Direction (2 of 3)
Speed 10 m/s
Velocity 10 m/s west
A car traveling north at 10 m/s turns left and
travels west at 10 m/s.
Velocity 10 m/s north
In this case, the cars speed stays constant at
10 m/s.
Speed 10 m/s
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Changing Direction (3 of 3)
Velocity 10 m/s west

• Acceleration occurs
• - whenever velocity changes
• when an object changes direction
• When an object changes speed.

The car accelerated when it turned left.
Velocity 10 m/s north
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Acceleration (1 of 1)
Acceleration occurs when any object

• starts moving

• speeds up

• turns a corner

• slows down

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Force and Acceleration (1 of 2)
You have seen that acceleration occurs whenever
an objects velocity changes.
What causes an objects velocity to change?
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Force and Acceleration (2 of 2)
An objects velocity changes when an unbalanced
force acts upon it. For
example, when something pushes or pulls it.
So, if an objects velocity changes when an
unbalanced force acts upon it, and acceleration
occurs whenever an objects velocity changes
Newtons law of force and acceleration states
that acceleration occurs when an unbalanced force
acts upon an object
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Unbalanced Forces (1 of 3)
Think of a tug of war.
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.
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Unbalanced Forces (2 of 3)
Owens two children, Luke and Lea, have
challenged him to a tug of war.
Owen can exert a pulling force of 4000 N.
Lea can pull a force of 2500 N, and Luke can pull
1000 N.
Who will win the tug of war?
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Unbalanced Forces (3 of 3)
First work out the total force that Luke and Lea
are exerting on the rope.
Luke and Lea total force 2500 N 1000 N 3500
N
Difference in force 4000 N 3500 N 500 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.
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Speed, Velocity and Acceleration (1)
What is the difference between speed, velocity
and acceleration?
Speed is the rate at which an objects position
changes.
Velocity is the speed of the object in a
specified direction.
Acceleration is the rate at which an objects
velocity changes.
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Question 1
"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.
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Question 2

• Displacement measures how far and in what
  direction an object is from its starting point.
• Is this statement True or False?
• True
• False

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Question 3
Which of the following can occur when an object
is accelerating?
A) The object speeds up
B) The object slows down
C) The object changes direction
D) All of the above
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Question 4

• 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?
• 20 m/s
• 5 m/s
• 200 m/s
• 10 m/s

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• Question 5
• What is the main difference between velocity and
  speed?
• Speed is used for low speeds while velocity is
  used for high speeds.
• Speed and velocity are measured in different
  units.
• Speed does not have to have a direction but
  velocity does.
• Speed is used to describe how vehicles move but
  velocity is used for all other movements.

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• Question 6
• In which region is the runner stationary?
• A) A-B
• B) B-C
• C) C-D
• D) D-E

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• Question 7
• Where is the runner accelerating?
• A) A-B
• B) B-C
• C) C-D
• D) D-E

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Question 8 Where is the runner moving at the
greatestt constant speed? A) A-B B)
B-C C) C-D D) D-E
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• Question 9
• Constant velocity is represented by a ___________
  line on a distance-time graph.
• Curved
• Straight
• Downward
• Bell shaped

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• Question 10
• Which of the following is a correct example of
  velocity?
• 10 m/h
• 10 West
• 10 m/h West
• West