What Is Physics?
One of the fundamental goals of physics is to investigate something that every-
one talks about: energy. The topic is obviously important. Indeed, our civilization
is based on acquiring and effectively using energy.
For example, everyone knows that any type of motion requires energy:
Flying across the Pacific Ocean requires it. Lifting material to the top floor of an
office building or to an orbiting space station requires it. Throwing a fastball
requires it. We spend a tremendous amount of money to acquire and use energy.
Wars have been started because of energy resources. Wars have been ended
because of a sudden, overpowering use of energy by one side. Everyone knows
many examples of energy and its use, but what does the term energyreally mean?
What Is Energy?
The term energyis so broad that a clear definition is difficult to write. Technically,
energy is a scalar quantity associated with the state (or condition) of one or more
objects. However, this definition is too vague to be of help to us now.
A looser definition might at least get us started. Energy is a number that we
associate with a system of one or more objects. If a force changes one of the
objects by, say,making it move, then the energy number changes. After countless
experiments, scientists and engineers realized that if the scheme by which we
assign energy numbers is planned carefully, the numbers can be used to predict the
outcomes of experiments and, even more important, to build machines, such as fly-
ing machines. This success is based on a wonderful property of our universe:
Energy can be transformed from one type to another and transferred from one
object to another, but the total amount is always the same (energy is conserved).
No exception to this principle of energy conservationhas ever been found.
Money.Think of the many types of energy as being numbers representing
money in many types of bank accounts. Rules have been made about what such
money numbers mean and how they can be changed. You can transfer money
numbers from one account to another or from one system to another, perhaps
CHAPTER 7
Kinetic Energy and Work
7-1KINETIC ENERGY
After reading this module, you should be able to...
7.01Apply the relationship between a particle’s kinetic
energy, mass, and speed.
7.02Identify that kinetic energy is a scalar quantity.Key Idea
Learning Objectives
149149●The kinetic energy Kassociated with the motion of a particle of mass mand speed v, where vis well below the speed of light, is
K^12 mv^2 (kinetic energy).