Summary
Scientists often devise models of physical phenomena.
A model is a kind of picture or analogy that seems to explain the phenomena.
A theory, often developed from a model, is usually deeper and more complex than a simple model.
A scientific law is a concise statement, often expressed in the form of an equation,
which quantitatively describes a particular range of phenomena over a wide range of cases.
Measurements play a crucial role in physics , but can never be perfectly precise.
It is important to specify the uncertainty of a crucial role in physics ,
but can never be perfectly precise .
It is important to specify the uncertainty of a measurement either
by stating it directly using the notation ,
and/or by keeping only the correct number of significant figures.
Physical quantities are always specified relative to a particular standard or unit ,
and the unit used should always be stated.
The commonly accepted set of units today is the Systeme International(SI),
in which the standard units of length , mass ,and time are the meter kilogram, and second .
When converting units ,check ,all conversion factors for correct cancellation of units.
Making rough ,order-of-magnitude estimates is a very
useful technique in science as well as in everyday life .
The dimensions of a quantity refer to the combination of vase quantities that comprise it .
Velocity ,for example, has dimensions of[length/time]or[L/T].
Working with only the dimensions of the various quantities in
a given relationship(this technique is called dimensional analysis)it
is possible to check a relationship for correct form.