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Energy!
Physics Investigation 3
By Amanda Brockbank and Ethan
Kessinger
What is energy?
• According to Conceptual Physics, energy is
“That property of an object or a system which
enables it to do work.”
• But what does this mean?
Work
• Lets start with a key word in that definition: Work
• Work is the action of putting an object into motion, and is what occurs
when we lift a load against gravity (so, the greater the gravity or load, the
more work required).
• Work can be calculated by multiplying force times distance (w=fd)
• It generally falls into two categories:
– Work against another force. For example, when you do a pushup, you are
working against your own weight
– Work to change the speed of an object. For example, when you speed up or
slow down a car.
• Work is measure in JOULES. One Joule of work is done when a force of 1
Newton is exerted over a distance of one meter. This makes sense when
you apply it to the aforementioned formula: work (in joules)=1 Newton x 1
meter. 1 x 1=1.
• On a larger levels, Joules can be measured as Kilojoules (kJ) or Megajoules
(MJ)
Power
• But what about how long it takes to do that work? Work is
an arbitrary number if we don’t have a sense of time. To
find how fast the work is done, we use power, the rate at
which work is done.
• Power is calculated by dividing work done by time
(power=work done/time interval)
– So, if an engine can get 12 joules of work done in 6 minutes, the
power is 2 watts
• As seen above, it is measure in WATTS. One watt is
expended when one joule of work is done in one second.
Again, this makes sense when it is applied to the formula.
FUN FACT: When we watch car commercials and we hear
about horsepower, it is actually referring to a unit of power
that equals .76 Kilowatts
• Now we have broken down the definition of
energy, which is a good starting point. But what
has energy? Almost everything does! Let’s take a
closer looks at the forms
Energy Forms
•Nuclear
•Radiant
•Chemical
•Electrical
•Mechanical
Nuclear/Atomic Energy
• Energy is formed from
changes in the structure
of the nucleus
•Nuclear Fusion
–Two or more atomic nuclei join together to
form a single heavier nucleus
•Occurs in nature
–Stars produce heat and light because of
nuclear fusion
•Nuclear Fission
–An atom’s nucleus splits into smaller
parts
•Man-made
–Take energy from reaction and use it to
heat water. This steam is then harnessed
as an energy source
Radiant Energy
•Energy that is
transferred by
electromagnetic waves,
or radiation
•Includes: Visible light, Gamma
Rays, and radio waves
Contrary to popular belief, solar energy
is not the only way we use the sun.
Radiant energy covers all of these
mediums. However, you must realize
that not all solar energy can be
harnessed
Chemical Energy
•Energy in bonds between
atoms
•Endothermic: Energy required to break
bond
•Exothermic: Broken bonds create new
molecules and give off heat
*Examples of chemical energy:
the body’s use of ATP, and
burning of coal
Electrical Energy
•Presence and flow of
an electric charge
•Current: Movement
of the charge
•Charge: Created by
Electrons and
Protons
Mechanical Energy
•The energy due to the position or movement of something.
•It can be potential energy, kinetic energy, or both
Kinetic Energy
• Kinetic energy is the energy of motion. It depends on
the mass of the object, and the speed of the object.
• To calculate the kinetic energy of an object, you can
use the equation kinetic energy=1/2mass x speed^2.
In equation notation, this is fd=1/2mv^2.
•Remember work? Technically its force times distance.
Since kinetic energy is abbreviated by fd, does that
mean they’re the same thing?
–Work is the act of putting an object into motion, and
kinetic energy is simply the energy of motion. They
are the same thing.
Potential Energy
• The energy that an object stores and holds in
readiness is called potential energy (it has
potential energy because the object has the
potential to do work).
Conservation and Transformation of
Energy
• But how does this matter in nature?
• Well, more than important than simply knowing what energy is, it is
important to know how it transforms.
• The law of conservations of energy states: “Energy cannot be
created or destroyed. It can be transformed from one form to
another, but the total amount of energy never changes.” In short,
energy is never created or destroyed, only transferred from one
form to another.
• We see this all the time in our lives: almost all processes or changes
occur partially due to the transformation of energy from one form
to another. Any time a change occurs, energy is present.
• Take, say, something as simple as the solar calculator you use for
math: this requires a transfer of energy as light (radiant energy) is
transformed to electrical energy.
Conservation of energy
•
This picture shows the transformation of energy coming from the sun as it
changes on earth. Clearly, it is never created or destroyed, as the law of the
conservation of energy dictates. Rather, the original nuclear energy coming
from the sun just changes forms and is transferred from one agent to another.
Machine
• A device used to multiple forces or to change the direction of
forces. Fundamentally, machines are just methods through
which energy can be transferred, since in cannot be created
or destroyed according to the law of the conservation of
energy.
• 6 Simple Machines:
1. Pulley
2. Lever
3. Wedge
4. Wheel and Axle
5. Inclined Plane
6. Screw
What are the sources of the different
types of energy?
• Chemical Energy: Stored in the bonds of atoms
and molecules.
• Mechanical Energy: Stored in objects by tension
(for example, a stretched rubber band is storing
mechanical energy)
• Nuclear Energy: As this is the energy that holds
the nucleus of an atom together, it is stored in
the nucleus of an atom.
• Electrical Energy: The movement of electrons and
negative charge.
• Radiant Energy: Found in electromagnetic waves
Energy Sources in the US
• Clearly, most of our energy
comes from fossil fuels.
However, if you trace this back
further, you will find that most
of the energy we use today
actually comes from the sun.
There is the obvious use of
solar energy, but when we
burn any sort of fossil fuel, we
are releasing chemical energy
that was stored in plants
millions of years ago, originally
coming from photosynthesis
and the sun.
Energy Transfer in Everyday Life
Wind Turbine
• Sun Heats the Earth, air rises and
creates wind: Radiant energy
• The wind blows and moves the
turbines: Kinetic Energy
• Turbines rotate that is captured by
the generator: Mechanical Energy
• Generator harnesses energy and
stores it: Electrical Energy