Transcript energy

Energy
Definition:
In general, the word energy refers
to a concept that can be defined
as "the potential for causing
changes", and therefore one can
say that energy is the cause of
any change
Forms of Energy
• Energy is found in different forms, such as
light, heat, sound and motion. There are
many forms of energy, but they can all be
put into two categories: kinetic and
potential.
KINETIC ENERGY
• Kinetic energy is
motion of waves,
electrons, atoms,
molecules,
substances, and
objects.
Electrical Energy
• Is the movement of electrical charges.
Everything is made of tiny particles called
atoms. Atoms are made of even smaller
particles called electrons, protons, and
neutrons. Applying a force can make some
of the electrons move. Electrical charges
moving through a wire is called electricity.
Radiant Energy
• Is electromagnetic energy that travels in the
space. Radiant energy includes visible light, xrays, radio waves and gamma rays.
• Solar energy is an example of radiant energy.
Thermal Energy
• Thermal energy or
heat, is the internal
energy in substances
• Geothermal energy is
an example of
thermal energy.
Motion Energy
• Is the movement of objects and
substances from one place to
another.. Wind is an example of
motion energy
• Objects and substances move
when a force is applied
according to Newton’s Laws of
Motion F = M*a
POTENTIAL ENERGY
• Potential energy is stored energy and the
energy of position––gravitational energy. There
are several forms of potential energy.
Chemical Energy.
Stored Mechanical Energy
Nuclear Energy.
Gravitational Energy
Chemical Energy
• Is energy stored in
the bonds of atoms
and molecules. It is
the energy that holds
these particles
together. Biomass,
petroleum, natural
gas, and propane are
examples of stored
chemical energy.
Stored Mechanical Energy
• Is energy stored in objects
by the application of a
force. Compressed
springs and stretched
rubber bands are
examples of stored
mechanical energy
Nuclear Energy
Is energy stored in the
nucleus of an atom
The energy that holds the
nucleus together can be
released when the nuclei
is split apart. Nuclear
power plants split the
nuclei of uranium atoms
in a process called
fission.
Nuclear Energy
• nuclear fusion is the
process by which multiple
nuclei join together. Later
we have a heavier
nucleus and the release
of energy
• Scientists are working on
creating fusion energy, so
that someday there might
be fusion power plants.
Gravitational Energy
• Is the energy of position
or place.
• A rock resting at the top
of a hill contains
gravitational potential
energy.
• Hydropower, such as
water in a reservoir
behind a dam, is an
example of gravitational
potential energy.
Conservation of energy
• The law of conservation of energy says
that energy is neither created nor
destroyed. When we use energy, it doesn’t
disappear. We change it from one form of
energy into another.
Conservation of energy
• Energy cannot be created
or destroyed but can only
be transferred from one
body to another or
change from one form to
another.
• A car engine burns
gasoline, converting the
chemical energy in
gasoline into mechanical
energy. Solar cells
change radiant energy
into electrical energy.
Energy Units and Conversions
• In the International System, energy is measured
in joules
• Joule (J) is the unit of energy, equal to the force
of one Newton acting through one meter.
• 1J = 1N*1m
There is another energy units, the calorie
• 1 calorie of heat is the amount needed to raise 1
gram of water 1 degree Centigrade.
• 1 calorie (cal) = 4.184 J
Energy Units and Conversions
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Calculate how many calories are:
a) 2005 joules
b) 3566 joules
Calculate how many joules are
A) 34545 calories
B) 5664 calories
Energy Units and Conversions
• Find the work
(energy) done when a
horse exert a
horizontal force of
400 N on a cart and
pulls it 20 m in the
direction of the force
Mechanical power
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Power is the rate at which work is done.
Power = work done / time taken.
The measured of power is watt ( W)
So if time is measured in seconds and
work in Jules:
• 1W = 1J/1s
Exercices
• Exercices 1º
• A car engine provides a forward force of
1000 N. If the car is travelling at 20 m s-1,
what power is developed?
• Remember that:
• work = Force multiplied by distance or
• W = F*D
Exercices
Solution
• In 1 s, the car travels 20 m. Hence we can
calculate:
• Work done in 1 s = force × distance =
1000 N × 20 m = 20 000 J = 20 kJ
• Power = work done / time taken = 20 kJ / 1
s = 20 kW.
Exercices 2
A man raises a object of mass 40 kg through a
vertical height of 20 m in 4 seconds. Find the
power.
Note: The potential energy is measured by the
following equation:
Pe = m x g x h
Where:
M = mass , g = 9,8 , h = height
Solution: 1960 W
Exercices 3
• A women run up a flight of 120 stairs in 30
seconds. If the height of each stair is 15
cm, find the power
• Solution: 294 watts
Exercices 4
4.1) A 100 watt electric heater is used to
heat water and bring it to the boil. If 5000 j
are needed to bring the water to the boil,
for how long is the heater operating?
• 4.2) How much energy is given out by a
60W bulb the is running 5 hours?