Transcript Energy

Nature of Energy
• Energy is all around you.
• You hear energy as sound, you
see energy as light, you can feel
energy in wind.
• Living organisms need energy
for growth and movement.
• You use energy when you hit a
tennis ball, compress a spring, or
lift a grocery bag.
• Energy is the ability to do
work.
Forms of Energy
• Energy appears in many forms.
• There are five main forms of energy.
– Mechanical
– Heat
– Chemical
– Nuclear
– Electromagnetic
• Electrical
Mechanical Energy
• The energy possessed by an object due to its
motion or position.
• Mechanical Energy is equal to potential
energy plus kinetic energy.
– ME = PE + KE
• Examples:
– A thrown baseball
– Water in a waterfall
Heat Energy
• The internal motion of atoms.
• The faster the molecules move, the more
heat energy is produced.
Examples:
Friction
Changes in state of matter
Chemical Energy
• Energy that exists in the bonds that hold atoms
together.
• When bonds are broken, chemical energy is
released.
Examples:
• Digesting food…bonds are broken to release
energy for your body to store and use.
• Fire…a chemical change.
Nuclear Energy
• The potential energy stored in the nucleus of
an atom.
• When the nucleus of an atom splits, nuclear
energy is released.
• Nuclear energy is the most concentrated
form of energy.
Electromagnetic
Energy
Energy that travels in waves,
such as ultra-violet radiation.
It can be thought of as a
combination of electric and
magnetic energy.
Example:
• Light is this form of energy (Xrays, radio waves, laser light, etc.)
Electrical Energy
• The energy associated with electric charges.
Examples:
• Power lines carry electrical energy into
your house = electricity.
• Batteries
Each of these forms of
energy is a combination
of
PE & KE.
Questions
• What is energy?
• What are the different forms of energy?
• Can energy be transferred from one object
to another?
States of Energy
There are two states of
energy:
Potential and Kinetic
Potential Energy
• A stretched rubber band has energy.
• Two magnets, when pulled apart, have
energy.
– The rubber band has energy because it’s stretched
rather than relaxed.
– The magnets have energy because they’re apart
rather than together.
Potential Energy
When something, or a group of things, has energy simply
because of relative position or shape, it’s known as
potential energy.
• A stretched rubber band has PE and thus the ability to do
something…
– snap back into place if you let go.
• Two separated magnets have PE and thus the ability to do
something…
– jump back together when you let them go.
Potential Energy
• Gravitational Potential Energy (GPE) – the
PE everything has because of its height above
the Earth’s surface.
• GPE = m g h (where m equals the mass of the object, g
equals 9.8 m/s2, and h equals the height of the object above
some surface)
Kinetic Energy
• Anything that is moving has a
special kind of energy known
as “moving energy.”
• This “moving energy” is called
kinetic energy.
– A rolling ball, a running dog, a
falling object, two magnets
heading towards each other, and
anything else in motion, all have
kinetic energy.
– The faster the object moves, the
greater the kinetic energy.
Kinetic Energy
• The kinetic energy of an object depends on
both its mass and its velocity.
– KE increases as mass increases.
– KE increases as velocity increases.
• Kinetic energy = ½ mass x velocity2
– KE = ½ mv2
Energy Conversions
The most common energy
conversion
involves the changing of
potential energy into
kinetic energy or viceversa.
1
2
3
1. At the top of the ramp, the marble’s ME is equal to its PE because the
marble has no velocity.
•
100% PE
2. As the marble goes down the ramp, it loses height but gains speed. The PE
lost is equal to the KE gained.
•
50% PE & 50% KE
3. As the marble speeds along the bottom of the ramp, all of the PE has
changed to KE. Total ME remains unchanged.
• 100% KE
Energy Conversions
• The Law of Conservation of Energy states that
energy cannot be created or destroyed, BUT can be
converted into other forms of energy.
• No matter how energy is transformed or
transferred, all of the energy is still present
somewhere in one form or another.
• As long as you account for all of the different
forms of energy involved in any process, you will
find that the total amount of energy never changes.
Your body converts chemical
energy stored in food into
thermal energy & mechanical
energy (muscle movement).
ENERGY