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OBJECTIVE At
the end of this lesson, students should be able to: 1. State the Law of
Conservation of Energy. Describe
how the energy of motion of an object depends upon the speed of the object. Why
does a ball bounce lower on each bounce than on the one before? Modern
Indy cars are designed to break into several pieces during collisions. The
pieces of the car carry away the energy of motion of the car so that the
driver doesn't absorb this energy and can escape uninjured. This is an example
of the Law of Conservation of Energy. THE LAW
OF CONSERVATION OF ENERGY THE
PHYSICS ENERGY: WHERE DOES IT COME
FROM? The
Law of Conservation of Energy states that energy is neither created nor In
the case of a racecar, the chemical potential energy stored in the fuel is
converted to the energy of motion of the car. Chemical potential energy that
is not transformed into the energy of motion of the car turns into heat. At
racing speeds, cars carry a considerable amount of energy of motion. When the
car collides with the wall or another car, the energy of motion must go
somewhere as the car comes to a stop. In
old-fashioned cars, the energy changed into elastic potential energy as the
car was crushed. Modern cars are designed to fly apart so that the pieces of
the car carry off much of the energy of motion that the car had going into the
collision. The "tub" in which the driver sits comes to a rapid stop
and is not deformed, thus protecting the driver.
SOME
THINS EXTRA Not
all of the energy of motion of the car is carried away by pieces of the car
during the collision. Some pieces are crushed, and part of the energy goes into
the elastic energy of deformation. Some of the remaining energy may go into the
deformation or break up of whatever the car hits. Ultimately, all the energy
involved in the collision is converted into heat and slightly raises the
temperature of the environment. During
normal stops, the car also loses its energy of motion. When the driver applies
the brakes of the car, the friction between the brake pad and the drum
transforms the energy of motion into heat. Under normal circumstances, the heat
produced is quickly carried away by air flowing around the brake. In extreme
cases, the heat builds up in the brake faster than the air can carry it away,
and the This
problem is particularly notable for large trucks coming down steep hills. As it
rolls down the hill, the truck converts gravitational potential energy into the
energy of motion. The very large mass of the truck means that it carries a great
deal of energy of motion. When it slows down repeatedly, it must generate more
heat than a less massive passenger car. Thus trucks are warned by highway signs
to use their engines to brake.
OTHER
EXAMPLES
You
must eat in order to get the chemical potential energy stored in food. The body
converts that energy into heat to keep you warm and into the energy of motion of
different parts of your body. If you eat more food than you A
roller coaster converts gravitational potential energy to the energy of motion
at the bottoms of the hills and back again to gravitational potential energy at
the tops. Some of the energy is changed by friction to heat of the rails and
wheels so that the coaster gradually loses energy and can't climb back up to the
top of the original hill. |
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destroyed but changes from one form to another. The total amount of energy
stays the same. 
Collisions
where wheels and other pieces of the car fly off at high speeds look like
disasters, but the disintegration of the car is actually a design feature in
order to protect the driver. 
brake overheats. 
When
a ball falls towards the floor, it has energy of motion. When it hits the floor,
the energy of motion is converted into the elastic energy of deformation of the
ball and a little heat. During the bounce, the energy of deformation is
converted back into energy of motion and a bit of heat. On its upward bounce,
the energy of motion of the ball turns into gravitational potential energy until
the ball comes to a stop with all its energy in the form of gravitational
potential energy. On the down bounce, it converts gravitational potential energy
to the energy of motion, and the process begins again. Each subsequent bounce is
lower than the preceding one because some energy is converted to heat each
time.
need to stay warm
and sustain your daily activities, the body will store the extra energy as the
chemical potential energy of fat.