Page 352 - ABCTE Study Guide_Neat

The other type of circuit is a parallel circuit. If the two bulbs are connected in a parallel circuit, the wire
has a junction with a wire going to each bulb. After the bulbs, the wires then join again at another junction.
The current is split between the two bulbs in this type of circuit.

Work and Energy

One of the most fundamental laws of science is conservation of energy:

Energy can change into a different form, but it can be neither created nor destroyed.

It can change forms, but the total amount of energy in a closed system must remain constant.

Mechanical energy can take the form of either potential energy or kinetic energy. Potential energy is
the energy due to an object's position. For example, a weight held above the ground has more
gravitational potential energy than the same weight lying on the floor. Kinetic energy is the energy that an
object has because it is moving. An object with either more mass or more speed will have a greater kinetic
energy.

When the temperature of an object increases, the random motions of the individual atoms and molecules
increase; so heat energy is just kinetic energy that is randomized at the molecular level. Energy can also
be stored in either electric or magnetic fields, hence light and other forms of electromagnetic radiation are
also forms of energy. The chemical energy that is released in a chemical reaction is the potential energy
stored by the electrical forces within the atoms and molecules involved in the reaction.

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Energy can interchange among any of these forms. Einstein's famous equation E=mc means that energy
can also take the form of mass. Mass and energy are interchangeable; the equation gives a formula for
finding the amount of energy equivalent to a certain amount of mass. In nuclear reactions, energy is
released because some of the mass in the atomic nuclei undergoing the reaction is converted into energy.

Question

A couple paragraphs up, you were holding a weight above the ground. If you let go of the weight and
allow it to fall to the floor, which of the following statements best describes the energy conversions from
the time the weight is overhead until just before it hits the floor?

A Potential energy is converted to kinetic energy.

B Kinetic energy is converted to potential energy.

C Potential energy is converted to heat.

D Kinetic energy is converted to heat.

Answer

The correct answer is A. When the weight falls, its gravitational potential energy is converted to kinetic
energy, and the weight moves at a higher speed. When the weight strikes the floor (or possibly your foot),
the kinetic energy goes into deforming or breaking the weight, floor, or possibly your foot, the sound
made, and so forth.