Energy Bikes
By Vanessa Knutson
Purpose: The purpose of this activity is to demonstrate the Law of Conservation
of Energy, to illustrate how different household items require different amounts of
energy, and to show ways we can conserve energy in our homes.
Background: As we know from the Law of Conservation of Energy, energy
cannot be created or destroyed, only converted from one type of energy to another.
Energy is vital to all of the organisms on the planet, including us. We humans
ultimately derive our energy from the sun. Through photosynthesis, plants convert
light energy into chemical energy, the energy stored in the bonds of molecules.
When we eat plants, we take in this
chemical energy, which we may
store for later use. We can convert
this chemical energy into
mechanical energy when we move
around, or heat energy to maintain
our body temperature. So although
energy may change forms, we never
actually create or destroy energy.
How this bicycle contraption
works
The bicycle rider has energy stored
in his or her body in the form of
chemical energy, which includes
carbohydrates and fats. Cells in his or her body will convert these chemicals into
another chemical called ATP (adenosine triphosphate), which is what our body
directly uses as fuel to do work. The rider must use ATP to get his or her muscles
to contract and ride the bike. At this step, energy is converted from chemical
energy to mechanical energy, the energy of movement. This energy is transferred
from the rider’s legs to the bike wheels. On the back of the bike, there is a
generator attached that converts this mechanical energy to electrical energy (think
of turbines or windmills). This electrical energy is then used to light up the bulbs
or other appliances, which give off either light or heat, both of which are forms of
energy.
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Conservation
Our energy bike demonstration helps illustrate different amounts of energy that we
consume at home or at work. As the rider rides the bike, at first, it is fairly easy to
pedal. The rider is not operating any electrical appliances at this time. Once the
lights and appliances are turned on, it becomes more difficult to pedal. It feels as
though you are trying to ride uphill! This is because it requires much more energy
to light up all those bulbs and appliances, just like it takes much more energy to
pedal up a hill than along a flat surface.
Remember the basic principle of
Conservation of Energy, “Energy is
neither created nor destroyed, it is only
changed in form.” The energy in the food
the rider ate is being changed into kinetic
energy of the moving bicycle tire which is
converted into electrical energy which in
turn is changed into light energy or heat
energy.
One way we demonstrate conserving
energy here (and in making it easier for
the rider to pedal the bicycle) is to replace incandescent bulbs with compact
fluorescent bulbs. Riding the bike shows you that it is far easier to supply enough
energy to light up the compact fluorescent bulbs than it is the incandescent bulbs.
An even better method of conserving energy is to turn the lights off when you
leave the room!
Questions/ Extension:
⇒ For which type of bulb (incandescent, compact fluorescent) is it harder to ride
the bike?
⇒ How can we conserve energy in our homes?
⇒ Where in this system does some energy leave?
⇒ Is that energy lost forever?
Special Thanks
Thank you to the Amgen Center for Science Learning at the California Science
Center for letting us use their energy bikes.