Download Energy Transformations and Energy Transfers

Energy Transformations
and Energy Transfers
Chapter 6
Forms of Energy
Energy – the capacity to do work
Example 1: Running

Chemical Energy – the energy is
stored by chemicals in your
muscles.

Kinetic Energy – your muscles start
you moving.

Thermal Energy (heat) – running
makes you hot and some of the
energy released in your muscles is
wasted as heat.
Example 2: Switching on a
light

Electrical Energy – flick of a
switch.

Light Energy – in the light bulb
electrical energy is transformed.

Thermal Energy (heat)- the light
bulb also produces heat.
Forms of Energy
Kinetic Energy (k.e.) – the energy of a moving object
Lets Review
Newton’s Three Laws
First Law – an object either remains at rest or continues to move at a constant
velocity, unless acted upon by a net force.
Second Law – the sum of the forces F on an object is equal to the mass m of that
object multiplied by the acceleration a of the object: F = ma
Third Law – when one body exerts a force on a second body, the second body
simultaneously exerts a force equal in magnitude and opposite in direction on the
first body.
Gravitational Potential Energy (g.p.e) – the energy of an object
raised up against the force of gravity.
Chemical Energy – energy stored in chemical substances and which
can be released in a chemical reaction.
Electrical Energy – energy transferred by an electric current.
Nuclear Energy – energy stored in the nucleus of an atom.
Strain Energy or Elastic Energy – energy of an object due to its
having been stretched or compressed.
Internal Energy – the energy of an object; the total kinetic and
potential energies of its particles.
Thermal Energy (heat) – energy being transferred from a hotter
place to a colder place because of the temperature difference
between them.
Light Energy – energy emitted in the form of visible radiation.
Sound Energy – energy being transferred in the form of sound waves.
Energy Stores and Energy Transfers
Transferring of Energy

By a force
Lifting something gives it
gravitational potential energy
Pushing something gives it
kinetic energy
Doing Work – transferring
energy by means of a force.

By heating
Energy spreads out from hot
objects
By radiation
Light from the Sun is
transferred to the Earth
Some is transferred as
infrared and ultraviolet radiation
Electromagnetic Radiation –
energy travelling in the form of
waves.
 By electricity
An electric current is a
convenient way of transferring
energy

Energy Conversions

When energy changes from one
form to another we say that it has
been converted or transformed
Energy conversion for a rocket
Conversation of Energy
Principle of Conservation of Energy –
the total energy of interacting objects
is constant provided no net external
force acts.
ENERGY CANNOT BE CREATED OR DESTROYED
Energy Efficiency
Efficiency – the fraction of
energy that is converted
into a useful form
Which bulb is more efficient?
Energy becoming dissipated (spread out)

Filament Lamp
Gravitational Potential Energy

Two Factors
1.
The object’s weight mg – the
greater the weight, the greater its
g.p.e
2.
The objects’s height h above
ground level – the greater the
height, the greater its gpe
A note on height
First

Sometimes think gradient

Sometimes height is constant
Second

It is the change in height of an
objects centre of gravity
Kinetic Energy (k.e.)
it takes energy to make things move
Kinetic energy depends on 2 factors

The object’s mass m – the greater
the mass, the greater its k.e.

The object’s speed v – the greater
the speed, the greater its k.e.