Transcript Activity 10 notes

Energy notes
Chapter 15
What is energy?
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The ability to do work
Work is done when an object has a
change in motion
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When a force causes something to move
through a distance, work is done.
Energy can be present when there is no
motion
Energy is observed only when it changes
forms
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Units: Joules (J)
1 joule = 1 Newton meter
1 calorie = 4186 joules
What is Kinetic Energy (KE)?
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The energy due to motion
KE = ½ m v 2
m
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= mass of runner
 v = speed of runner
Anything in motion has kinetic energy
KE depends more on speed than on
mass b/c of the squared term.
Kinds of Potential
Energy
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What is Potential Energy (PE)?
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Stored energy or Energy due to position
Units: Joules
Spring Potential Energy – the energy stored in
anything stretched, bent or compressed
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This gives the object the ability to cause something else
to move.
SPE = ½ k x 2
k = the spring constant of the stretchy object, (more
stretchy, lower k)
x = the amount stretchy object is displaced from start
Kinds of PE
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Gravitational Potential Energy – the
energy stored in an object because it
has height.
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GPE = mgh
m = mass of object
g = 10 m/s/s, the acceleration due to
gravity
h = the height of the object as measured
from a reference point.
Other forms of energy
Mechanical energy– deals with motion and
position of objects
Thermal energy – the total potential and kinetic
energy of all the particles in an object
Chemical energy – the energy stored in the
chemical bonds
Electrical energy – the energy associated with
electrical charges
Electromagnetic energy – a form of energy that
travels through space in the form of waves
Nuclear energy – the energy stored in atomic
nuclei
Law of Conservation of Energy
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Energy can not be created nor destroyed.
 It only changes forms
 Energy doesn’t appear out of nowhere.
 Energy doesn’t disappear.
At any given time, the total energy
remains the same.
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Ex. A flashlight – chemical energy in the
battery is converted into electrical energy when
the switched on, which is converted into heat
and light energy.
Roller coaster energy
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What energy
transformations
occur in a roller
coaster?
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The conveyor belt does work
on the car to give it
gravitational potential energy
at the top of the hill.
Then the car goes down the
hill and the potential energy
changes to kinetic energy.
Some of the potential energy
is changed to heat and sound
energies.
At the bottom of the hill, there
is no more potential energy
b/c the car can go no lower.
Then as the car goes up the
next hill, most of the kinetic
energy changes back to
potential energy.
Heat transfer
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Heat – energy that flows as a result
of a difference in temp.
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heat energy flow from hot objects to
cold objects
when molecules have thermal energy
added to them, they move faster and
bounce into each other, increasing their
kinetic energy, which causes the
particles to be pushed further apart
3 Methods of Heat Transfer
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Conduction – Heat transfer from particle to particle
of 2 materials touching each other. Usually occurs
between 2 solids. “Hot” particles bounce off each
other then transfer their energy to the cold particles.
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Pot on stove
Spoon in hot chocolate
Convection – Heat transfer by movement of a
heated substance by currents in a fluid (liquid or gas).
The energy gets transferred by a warmer fluid moving
through a colder fluid.
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Hot air popcorn poppers, convection ovens
radiators where hot water flows through
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Radiation – Transfer of electromagnetic
energy given off by “hot” materials that
can be transmitted through objects or a
vacuum at the speed of light. (No matter
needed)
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solar energy
Light
ultraviolet rays
Microwave ovens