Transcript Energy - Solon City Schools

Energy
What the heck is energy anyway?
• Energy- the ability to do work
• If an object or organism does work (exerts a
force over a distance to move an object) the
object or organism uses energy.
•
Work = force x distance
•
ex. When stretching a sling shot,
you do work, and energy is
transferred to the sling shot
• Measured in the unit joules
• b/c work is a force x distance it is measured in
Newtons x meters. These units are called
joules.
•
1 N x m = 1 J= 1 kg x m2/s2
Energy
• 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
Nature of Energy
• Energy is all around you!
– You can hear energy as sound.
– You can see energy as light.
– And you can feel it as wind.
Nature of Energy
Living organisms need energy
for growth and movement.
Types of Energy
• 1. Potential energy- energy that an object has
b/c of its position, shape, or condition of the
object
• Called “energy of position” or “stored
energy”
• Stretched rubber band has potential energy b/c
the 2 ends are far away from each other (elastic
potential energy)
Gravitational potential energy
• Gravitational potential energy- any
system of 2 or more objects separated by
a distance; results from gravitational
attraction b/w the objects
•
ex. Apple in a tree
• Grav. PE = mass x free-fall acc. X height
• PE = mgh
Gravitational Potential Energy
• An apple at the top of the tree has more grav.
PE w/ respect to the Earth than a similar apple
on a lower branch.
• But if two apples of different masses are at
the same height, the heavier apple has more
grav. PE than the lighter one
Types of Energy
• 2. Kinetic Energy- energy of a moving object
due to the object’s motion
-depends on mass & speed
Kinetic energy = ½ x mass x speed squared
KE = ½ x mv2
• in the KE equation, speed is squared so a small
increase in speed produces a large increase in
KE
ex. Why car crashes are more dangerous at
high speeds
• Atoms/molecules have KE b/c they are
constantly in motion (KE ↑ as particles heat up
or KE ↓ as particles cool down)
Mechanical vs. Nonmechanical potential energy
• A. Mechanical potential energy – energy that you can
see on a large scale; you know that it is there b/c of the
height ;
• Mechanical potential energy exists because of the
relative positions of two or more objects. For example,
a rock resting
on the edge of a cliff in such a position that it
will fall freely if pushed has mechanical potential
energy.
• Water at the top of a dam has mechanical potential
energy. A sled that is being
held at the top of an icy hill has mechanical
potential energy.
• B. Non-mechanical potential energy- energy that you
CANNOT SEE that is present in chemical bonds
•
ex. dynamite
Mechanical vs. Nonmechanical Kinetic energy
• A. Mechanical kinetic energyKinetic energy exists because of the relative
velocities of two or more objects.
• Examples: If you push that rock, open the gate of the
dam or let go of the sled, something will move.
• The rock will fall; the water will flow; the sled will
slide down the hill. In each case the mechanical
potential energy will be changed to mechanical
kinetic energy. Another way of saying this is that
the energy of position will be changed to the
energy of motion. This is energy that is clearly visible;
an object is moving.
• B Non-mechanical kinetic energy –energy that is NOT
VISIBLE but you know that it is there b/c it is present in
the atoms of a molecule (moving)
•
ex. Solid, liquid, gas atoms moving (dance moves)
Kinetic Energy
Types of Energy
• 3. Mechanical energy- sum of the
potential & kinetic energy in a system
• ex. Apples have potential energy when
they are hanging above the ground, & they
have kinetic & potential energy when they
are falling
•
ex. Roller coaster
Non-mechanical Energy
• Energy that lies at the level of atoms &
that does not affect motion on a large
scale is sometimes called nonmechanical energy.
Can mechanical energy change to
non-mechanical energy?
• Yes, as a result of air resistance and
friction.
• Moving an object across another can
result in heat through friction. This is
conversion of the mechanical energy into
thermal energy.
• In an electric motor, the (mechanical)
rotation of the coils results in electrical
current and therefore electrical energy.
Types of Energy
• 4. Chemical Energy- The amount of
chemical energy associated w/ a
substance depends in part on the relative
positions of the atoms it contains
• formation of bonds and the breaking of
bonds during chemical reactions
•
ex. Burning a match
• B/c chemical energy depends on
position, it is a kind of potential energy
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.
• Sports… your body uses energy
stored in your muscles obtained
from food.
• Fire–a chemical change.
Chemical Energy
• Fuel and food
are forms of
stored
chemical
energy
(potential).
Types of Energy
• 5. Nuclear Energy- kind of potential
energy stored by the forces holding
subatomic particles together in the nuclei
of atoms
• Nuclear Fusion- a type of reaction in
which light atomic nuclei combine to form
a heavier nucleus
•
ex. How sun works
• Nuclear Fission- a single heavy nucleus
is split into 2 or more lighter nuclei
Types of Energy
• 6. Electricity- results from the flow of
charged particles through a wire or other
conducting materials
• Lightning is caused by electrons traveling
through the air b/w the ground & a
thundercloud
Types of Energy
• 7. Electromagnetic Energy (Light)travels from the sun to the Earth across
empty space in the form of
electromagnetic waves
Electromagnetic Energy
• Light is a form of
electromagnetic energy.
• Each color of light (Roy G Biv)
represents a different amount
of electromagnetic energy.
• Electromagnetic Energy is
also carried by X-rays, radio
waves, and laser light.
Types of Energy
• 8. Thermal Energy is the kind of energy that is
related to and/or caused by heat.
• When you boil a pot of water, you are
contributing thermal energy or heat to the
bottom of the pot. This thermal energy is then
transferred to the water inside the pot.
• As the water molecules move faster (kinetic
energy), they begin to get hotter. As they move
faster and faster, each one tries to leap away
from its neighbors and into the surrounding air to
form water vapor, or steam. Once the water
starts boiling, it turns into steam very quickly!