TOPIC 1.
REVIEW
INTRODUCTION
In Physics 112 we will be making heavy use of vectors, so we will start with a review of
vectors.
The important vector quantities we will be discussing are electric forces, electric fields,
electric currents, magnetic forces, magnetic fields, and the velocity of propagation of
electromagnetic waves.
We will also be making heavy use of the concepts of mechanical energy, kinetic energy,
potential energy, and work
both conservative and nonconservative
so we will review these,
emphasizing gravitational forces.
Topic 1A.
Vectors
PHYSICAL QUANTITIES
Physics deals over and over with physical quantities
quantities such as mass,
temperature, force, acceleration, moment of inertia.
Sometimes you are given their values in a
problem.
Sometimes you have to measure them, as in a laboratory.
Sometimes you calculate
them from other quantities.
Sometimes you predict what their values will be at some time in the
future, say 15.0 seconds from now, or when a object rolling down a hill reaches the bottom of the
hill.
SCALAR PHYSICAL QUANTITIES
Some physical quantities are just a number, without units.
An example of such a physical
quantity is the coefficient of kinetic friction.
It has a value such as 0.55 or 0.13, with no units of
any kind.
That's because it is really a ratio of two forces, so the units cancel out.
These
quantities are referred to as
.
scalars
Other physical quantities are specified by a numerical value and a unit.
Together, the
numerical value and the unit are referred to as the magnitude of the quantity.
For example, an
object might have a mass of 5.0 kilograms.
"5.0" is the numerical value of this mass, and
"kilograms" refers to the unit.
With different units the numerical value is different, but the
magnitude is the same.
This mass, for example, could also be said to have a mass of 0.0050
megagrams, or 5000 grams.
These quantities are also referred to as scalars.
VECTOR PHYSICAL QUANTITIES
Some physical quantities have a magnitude but also require the specification of a
direction in space.
An example is the force acting on an object.
It might be "4.7 newtons south"
or "2500 newtons in an upward direction."
Or the velocity of an automobile might be "55 miles
per hour east" or "60 miles per hour west."
Physical quantities that require a direction in order to
be completely specified as referred to as
.
vectors
In summary, then, a scalar is a quantity that is completely specified by a magnitude
(whether or not it has units).
A vector is a quantity that is completely specified by a magnitude
and a direction.
The magnitude of a vector is itself a scalar.