The Physics
Hypertextbook
Opus in profectus

## Summary

• Physical quantities come in several types.
• The type of physical quantity determines the type of mathematics used.
• Only two types are dealt with in this book: scalar quantities and vector quantities — usually shortened to scalars and vectors.
Physical quantities compared
aspect scalars vectors
definition a quantity with
magnitude only
a quantity that with
magnitude and direction
directions   up, down, left, right
north, east, west, south
forward, backward
parallel, perpendicular
positive, negative (in a coordinate system)
bearing angle
angle of inclination, depression
angle with the vertical, horizontal
uptown, downtown, crosstown
etc.
examples distance
time (classical)
speed

mass
energy
surface area
volume
density
displacement
proper time (relativistic)
velocity
acceleration
force
weight
momentum
projected area
fields higgs field gravitational field, electromagnetic field, strong nuclear field, weak nuclear field
mathematics arithmetic:
sum, difference
multiplication
trigonometry:
resultant or net (Σ), change (Δ)
dot product (·), cross product (×)
with a unit
a number and a direction angle, both with units
-or-
a number with a unit for each unit vector ()
-or-
an arrow drawn to scale in a specific direction
• Parallel vectors behave like numbers on a number line.
• Add the magnitudes of vectors in the same direction.
• Subtract the magnitudes of vectors in opposite directions.
• Perpendicular vectors behave like points on a coordinate plane.
• Use Pythagorean theorem to determine magnitude.
• Use the tangent function to determine direction.
• Vectors in standard position have a common origin and are used in the parallelogram rule of vector addition
1. Construct a parallelogram using two vectors in standard position.
2. The resultant is the diagonal of the parallelogram coming out of the common vertex.
3. Your diagram should look like a parallelogram made of vectors. (Note: When the two original vectors are perpendicular, the parallelogram will be a rectangle.)
• Vectors arranged head to tail (with the tail of the second vector placed on the head of the first) are used in the triangle rule of vector addition.
1. Given two vectors arranged head to tail.
2. The resultant is the vector drawn from the tail of the first to the head of the second.
3. Your diagram should look like a triangle made of arrows. (Note: When the two original vectors are perpendicular, the triangle drawn will be a right triangle and the resultant will be a hypotenuse.)