PHY 185, EXPERIENCING THE PHYSICAL WORLD,
X - 4
WORK AND ENERGY
The theme for this week is Work and Energy. The activities illustrate
the relationship between work and energy and the conversion of energy from
one form to another. Also included is a video about preconceptions and
misconceptions in science. One of the things we are trying to do in this
course is to present the basic physics concepts necessary to for you to
recognize preconceptions that are misconceptions such as those illustrated
in the video.
1. VIDEO: "A PRIVATE UNIVERSE"
Includes exit interviews conducted at a Harvard University graduation
ceremony concerning the question of why we have seasons.
2. JUMPING DISK
The "Physics is Fun at Miami" jumping disk has become world famous
through its annual appearance in the Edmund Scientific Catalog. It is a
bimetalic disk that operates on the principle of differential expansion.
Warm the disk in your hand and fingers and press on the convex non-Miami
side until it clicks. Put the disk on a hard, smooth, relatively cool surface
and wait until it returns to its original shape. As the disk snaps back
to its original shape, it exerts a force on the table top. According to
Newton's Third Las, the surface pushes back on the disk performing work
on the disk. The work done on the disk is transformed, according to the
work-energy principle, into kinetic energy, which in turn is transformed
into gravitational potential energy (as gravity does negative work
on the disk as it travels upward, eventually slowing the disk to a stop).
On the way down, gravity does positve work on the disk and increases the
disk's kinetic energy. Analyze the motion of the disk for yourself, step-by-step,
and relate it to the work-energy principle.
3. CELT (pronounced kelt) or RATTLEBACK
This is an asymmetrically-shaped object that can reverse its spin
direction. Spin it in its non-preferred, or clockwise, direction and it
will "rattle" (oscillate) and reverse it's spin direction. Spin it in its
preferred, or counterclockwise, direction and it will continue spinning
without reversal. Tap it gently on either end causing it to "rattle" and
it begins spinning in its preferred direction. The asymmetric bottom raises
the center of gravity of the celt when it spins in its non-preferred direction,
transforming kinetic energy into gravitational potential energy. As the
celt rattles, comes to a stop and reverses, the potential energy is transformed
back into kinetic energy. This behavior is similar to that of a ball rolled
up an inclined plane.
4. ROLLBACK CAN
The work done on the can is transformed into kinetic energy, which
is transformed into the potential energy of an elastic or rubber band inside
the can as the can slows and stops. The elastic potential energy is then
transformed back into kinetic energy as the can rolls back to its starting
position.
5. PUSH AND GO CAR
The work done in pushing the car is transformed into kinetic energy
of the car, which is transformed into the potential energy of a spring
inside the car. When the button is pushed, the spring is released, and
the spring potential energy is transformed back into kinetic energy of
the car.
6. SPRING SHOES
Formerly worn by PhysicsMan while leaping over Culler Hall.
7. BOWLING BALL PENDULUM
Release the ball from your nose and remain motionless
as the ball swings out and returns to its starting position. If you believe
that transformation of energy does not increase the amount of energy, you
will not move. Caution, release the ball and do not push
on it, because the work done on the ball will result in an additional initial
kinetic energy for the ball and possible damage to your nose.
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