Chapter 3, Problem 3.1QP

Define these terms: potential energy, kinetic energy, law of conservation of energy.

Interpretation Introduction

Interpretation: The concept of potential energy, kinetic energy and law of conservation of energy should be explained.

Concept Introduction:

Energy is the ability to do work or transfer heat where work is the movement of a body using some force.  The SI unit of energy is joule (J).  Energy can be in the form of kinetic energy or potential energy.

Potential energy is the energy possessed by virtue of position.  Other forms of potential energy are chemical energy and electrostatic energy.  Kinetic energy is the energy associated with motion.  One of the forms of kinetic energy is thermal energy.  The law of conservation of energy states that energy can neither be created nor destroyed.

Explanation of Solution

Potential energy and Kinetic energy

The chemical and electrostatic energy are the two forms of potential energy.

Chemical energy is defined as the energy which is stored in the bonds of chemical compounds (molecules and atoms).  It is released in the chemical reaction and mostly produces heat as a by-product, known as an exothermic reaction. The examples of stored chemical energy are biomass, batteries, natural gas, petroleum and coal. Mostly, when the chemical energy is released from a substance, it is transformed into a new substance completely.  For instance, when an explosion goes off, the chemical energy in it is transferred into the surroundings as thermal energy, kinetic energy and sound energy.  Example: The dry wood is the storage of chemical energy. When it burns, the chemical energy is liberated and converted into light energy and thermal energy. Please note that the wood transforms into ashes which is a new substance.

Electrostatic energy is potential energy which results from the interaction of charged particles.  Oppositely charged particles attract each other and particles of like charges repel each other.  The magnitude of the resulting electrostatic potential energy is proportional to the product of the two charges (Q1 and Q2) divided by the distance between the two charges (d).

$\text{E}\propto \frac{{\text{Q}}_{\text{1}}{\text{Q}}_{\text{2}}}{\text{d}}$

If the charges ${\text{Q}}_{\text{1}}{\text{ and Q}}_{\text{2}}$ are opposite (i.e., one positive and one negative), Eel gets a negative value which indicates attraction.  Like charges (i.e., either both positive and both negative) result in a positive value for Eel which indicates repulsion.

One of the forms of kinetic energy is thermal energy.

Thermal energy is the internal energy of an object due to the kinetic energy of its atoms and/or molecules. The atoms and/or molecules of a hotter object have greater kinetic energy than those of a colder one, in the form of vibrational, rotational, or, in the case of a gas, translational motion.  For example, a hot brick has a greater kinetic energy than a cold brick.

The law of conservation of energy

Energy can be neither created nor destroyed.  When energy of one form disappears, the same amount of energy must appear in other form/forms. This principle is known as the law of conservation of energy.  Kinetic and potential energy are interconvertible, i.e., one form can be converted to the other.  For example, dropping an object and allowing it to fall converts potential energy to kinetic energy.

Conclusion

The concept of potential energy, kinetic energy, law of conservation of energy is explained.