Transcript Mechanical Energy:

Mechanical Energy:
Potential Energy and
Kinetic Energy
Day 2
Curriculum
• Big Idea: Energy can be transferred
between objects and/or can be
converted into different forms.
• Concept: Energy is conserved (Law of
conservation of energy).
PA Standard 3.2.C.B3: Describe the law of
conservation of energy.
Today’s Agenda – 10/28/10
•
•
Opener: What is energy?
Test of Courage: The Pendulum (see energy packet
and powerpoint)
• Challenge: Pendulum online lab simulation
• Answer Concept Questions: in the powerpoint
• Problem Solving: Pendulums and Rollercoasters
(in packet)
• Closure: Re-answer the “What Do You Think?”
Questions (on a note card).
Take Home Assignment: #6 - #10 on page 119 in
Conceptual Physics
Review:
A ball was dropped off a cliff.
• What happened to the PE?
The PE decreased as the ball’s height
decreased.
• What happened to the KE?
The KE increased as the ball’s velocity
increased.
• What happened to the PE + KE?
The PE + KE stayed the same
Concept Question
• When the pendulum swings back and
forth, do you think that the total energy
(PE + KE) increases, decreases, or stays
the same?
a. The total energy increases
b. The total energy decreases
c. The total energy stays the same
• If there were no outside forces on the pendulum,
the total energy of the pendulum would stay the
same (conservation of energy).
• The PE + KE of the pendulum actually
decreases. We can tell that its energy decreases
because the pendulum slows down and
eventually stops moving. Energy is still
conserved. Go on to the next concept
question…
Concept Question
• In terms of energy, why will you never get
hit by the pendulum (as long as you don’t
give it a push)?
a. Energy transfers from the pendulum to the air
in the form of heat.
b. Energy in the pendulum disappears.
c. The pendulum continuously gains energy from
its surroundings.
d. The pendulum always reaches its initial
height, even WITH friction and air resistance!
•
•
•
•
•
Energy is conserved
The pendulum system loses energy.
The energy did not disappear.
Energy is always conserved.
In this case, some energy is transformed
into heat due to air resistance. Heat is
another form of energy. The pendulum
heats up the air!
Challenge:
Pendulum Online Lab Simulation
As a class, change the air resistance for
the pendulum in the following online lab
simulation using the interactive white
board in the front of the class, and see if
you can match up the frequency of our
pendulum in class to the pendulum online
so that we can theoretically find the air
resistance on our pendulum:
• http://phet.colorado.edu/sims/pendulumlab/pendulum-lab_en.html
Pendulum Problem
Pendulum Problem
How does gravity affect PE?
http://www.youtube.com/watch?v=5C5_dO
EyAfk
How does gravity affect PE?
http://jersey.uoregon.edu/AverageVelocity/
Roller Coaster Problem
Key Terms
• energy: the property of an object or a
system that enables it to do work;
measured in joules.
• kinetic energy: energy of motion,
equal to half the mass multiplied by
the speed squared.
Key Terms
• potential energy: energy of position,
usually related to the relative position of
two things, such as a stone and Earth, or
an electron and a nucleus.
• Law of Conservation of Energy: Energy
cannot be created or destroyed. It may be
transformed from one form into another,
but the total amount of energy never
changes.
Closure
• Re-answer the “What Do You Think?”
Questions on a note card