Download Kinetic Energy

1. Can you write the title
of the new unit
Energy, work and power
and date
2. stick in the revision
topic list.
3. How many types
(forms) of energy can
you remember?
DO NOW!
Do now!
James Prescott Joule
1818 - 1889
4 Books in at end of
class
Learning today
• Work done
• W.D = Forces x distance in the direction of the force.
• The Joule J the unit for both
energy and work done
• What is energy
• Types of energy
Work done - copy please
When any object is moved around work will need to be
done on it to get it to move (obviously).
We can work out the amount of work done in moving an
object using the formula:
Work done = Force x distance moved
in direction of the force
in J
joules
in N
newtons
in m
meters
F
W
d
Question 1
Calculate the work done when a force of
5 newtons moves through a distance of
3 metres.
work = force x distance
= 5N x 3m
work = 15 joules
Question 2
Calculate the work done when a force of
6 newtons moves through a distance of
40 centimetres.
work = force x distance
= 6 N x 40 cm
= 6 N x 0.40 m
work = 2.4 joules
Now do
• Make Force the
subject of the
equation
• Make distance the
subject of the
equation
W
F
d
Question 3
Calculate the value of the force required to
do 600 joules of work over a distance of 50
metres.
work = force x distance
becomes:
force = work done ÷ distance
= 600 J ÷ 50 m
force = 12 newtons
Question 4
Calculate the distance moved by a force of
8 newtons when it does 72 joules of work.
work = force x distance
becomes:
distance = work done ÷ force
= 72 J ÷ 8 N
distance moved = 9 metres
Example questions
1. Bori pushes a book 5m along the table with a force of 5N.
He gets tired and decides to call it a day. How much work
did he do?
2. Alicia lifts a laptop 2m into the air with a force of 10N.
How much work does she do?
3. Martin does 200J of work by pushing a wheelbarrow with a
force of 50N. How far did he push it?
4. Chris cuddles his cat and lifts it 1.5m in the air. If he did
75J of work how much force did he use?
5. Carl drives his car 1000m. If the engine was producing a
driving force of 2000N how much work did the car do?
Question 5
Calculate the work done by
a child of weight 300N who
climbs up a set of stairs
consisting of 12 steps each
of height 20cm.
work = force x distance
The child must exert an
upward force equal to its
own weight.
Therefore: force = 300N
This force is exerted
upwards and so the
distance must also be
measured upwards.
= (12 x 20cm)
= 2.4m
therefore:
work = 300 N x 2.4 m
work = 720 J
What is Energy?
What is Energy?
“The capacity to do work”
Not a very good
definition!
Energy measurement – Copy please
Energy is measured in joules (J)
To lift an apple 0.1 kg upwards
by one metre requires about one
joule of energy.
1 kilojoule (kJ) = 1 000 J
103 J
1 megajoule (MJ) = 1 000 000 J
106 J
Types of energy
Energy can take many forms;
Now list the different types of
energies in the following two groups
Kinetic Energy –
movement energy
Potential Energy – energy
due to position or shape
or stored energy
Forms of energy
Energy can exist in many forms.
1. THERMAL
or HEAT ENERGY
This is the energy of an object
due to its temperature.
2. LIGHT ENERGY
This is energy in the form of
visible electromagnetic
radiation.
Light
5. KINETIC ENERGY
This is the energy possessed
by a moving object.
Kinetic energy increases is the
object’s speed is increased.
Also often called ‘Movement
energy’
A kicked football has 50J of
energy
Kinetic (movement)
3. ELECTRICAL ENERGY
This is the energy transferred
by an electric current.
4. SOUND ENERGY
This is energy in the form of a
sound wave.
Chemical
Nuclear
6. CHEMICAL ENERGY
This is energy that is released
when chemical reactions take
place.
Sources of chemical energy
include: fuel, food and
batteries.
Energy in one chocolate
biscuit 300 000 J
Energy in the food you in one
day 11 000 000 J
7. NUCLEAR ENERGY
This is energy that is released
when nuclear reactions take
place.
This is the source of the
Sun’s energy.
Gravitational potential
8. POTENTIAL ENERGY
This is the energy possessed an object due
to its position.
Gravitational Potential Energy
The gravitational potential energy of an
object increases if it is raised upwards.
Elastic Potential Energy
This is the energy
stored in a stretched
or squashed object
- also known as strain
energy
Gravitational
potential energy
being converted
into kinetic energy.
Strain
• A fully flexed
bow stores
around 300J
of energy
Now list the different types of
energies in the following two groups
Kinetic Energy –
movement energy
Potential Energy – energy
due to position or shape
or stored energy
•
•
•
•
•
•
•
•
•
Thermal
Light
Sound
Electric
Kinetic
Chemical
Gravitational
Strain
Nuclear
The Law of Conservation of
Energy
Energy can be changed
(transformed) from one
type to another, but it can
never be made or
destroyed.
This means that
the total amount of
energy in the
Universe stays the
same!
\
Energy Flow diagrams
We can write energy flow diagrams to show
the energy changes that occur in a given
situation.
For example, when a car brakes, its kinetic
energy is transformed into heat energy I the
brakes.
Kinetic
heat
Other examples
When a rocket launches.
Other examples
When a rocket launches.
Chemical
kinetic + sound + heat
gravitational
Energy Circus
Around the room are a few examples of
energy changes (some simple, some a little
more complicated!)
For each example I want you to write the
name of the experiment and then the energy
flow diagram for that experiment
You will have 2 minutes on each example.
Ready?
Go!