Page 160 - Microsoft Word - LessonPlan-Overview.doc
P. 160
Unit 5: Energy (Part 2) Page 10
That ball has: PE=mgh kept losing height. Also, as the ball
dropped it gained kinetic energy
2
PE= 1 kg x 10 m/s x 2m because it kept gaining speed. So,
PE= 20 Joules when the potential energy was .7
the kinetic energy was 0 (not
It has the potential to hit the floor moving). When the kinetic energy
with 20 Joules of energy. was .7 the potential energy was 0
(no height). All the energy
Transfer of Energy transfers during the fall.
Now’s a good time to introduce Energy Efficiency
another concept here, transfer of
energy. Energy changes to other Now here’s a question you may be
forms of energy all the time. The asking yourself, “If energy is
electrical energy coming out of a neither created or destroyed in a
wall socket transfers to light closed system then why doesn’t a
energy in the lamp. The chemical kid swinging on the playground
energy in a battery transfers to swing go forever?
electrical energy which transfers to
sound energy in your personal Ahhh, that’s a very intelligent
stereo. In the case of the ball question. You must be very smart!
falling, gravitational potential Energy is neither created or
energy transfers to kinetic energy, destroyed, but it can be transferred
the energy of motion. into non-useful energy. In the case
of the swinging kid (picture a
Conservation of Energy pendulum), every swing loses a
little bit of energy, which is why
Energy cannot be created or each swing goes slightly less high
destroyed in a closed system. A (achieves slightly less PE) than the
system is the place the energy is swing before it.
happening in. In this case, the
system is the ball dropping and Where does that energy go? To
hitting the flour. If the system is heat. The second law of
closed, that means no energy can thermodynamics states basically
get in or escape from the system. that eventually all energy ends up
Since that ball started with .7 as heat. If you could measure it,
Joules of energy, it hit the flour you’d find that the string, and the
with .7 Joules of energy and weight have a slightly higher
transferred .7 Joules of energy to temperature then they did when
the flour. No energy was created or they started due to friction.
destroyed, just transferred within
the system. As the ball dropped it The energy of your pendulum is
lost potential energy because it lost to heat! If you could prevent
the loss of energy to useless
© 2010 Supercharged Science www.ScienceLearningSpace.com
160
