College Physics Young 9e Chapter 1

Physics is an experimental science. Physicist observe the phenomena of nature and try to discover patterns and principles that relate these phenomena. These patterns are called physical theories or, when they are very broad and well established physical laws.

The development of a physical theory requires creativity at every stage. The physicist has to learn to ask appropriate questions, design experiments to try to answer the questions and draw appropraite conclusions from the results.

Developing a physical theory is always a two way process that starts and ends with observations or experiments. Physics is not a collection of facts and principles it is the process by which we arrive at general principles that describe the behavior of the physical universe. And there is always the possiblity that new observations will require revision of a theory. We can disprove a theory by finding a phenomenon that is inconsistent with it but we can't prove a theory is always correct

Principles that are so solidly established by experiemental evidence that they are considered physical law.

In physics a model is a simplified version of physical system that would be too complicated to analyze in full without the simplifications.

any number that is used to describe an observation of a physical phenomenon quantitatively

Some physical quantities are so fundamental that we can define them only by describing a procedure for measuring them. These are called operational definitions. In other cases we define a physical quanitity by describing a way to calculate the quantity form other quantities that we can measure.

We might use a ruler to measure a length or a stopwatch to measure a time interval. As an example of a quantities we calculate, we might define the avergae speed of a moving object as the distance traveled (measure with a ruler) divided by the time of travel (measured with a stopwatch).

1889-1967 was the unit of time in terms of the length of the day directly related to the time of the earth's rotation. Current: is based on the atomic clock that uses the energy difference between the two lowest energy states of the cesium atom. Electromagnetic radiation of precisl the proper frequency causes transitions from one of these states to the other. One second is defined as the time required for 9, 192, 631, 770 cycles of this radiation.

1983 to present: the meater is the distance light travels in vacuum in 1/299, 792,458 second this defines the speed of light at 299,792,458 m/s we then define the meter to be consistent with this number and with the atomic-clock definition of the second

The standard of mass is the mass of a particular cylinder platinum-iridium alloy. Its mass is defined to be 1 kilogram, and it is kept at the International Bureau of Weights and Measures at Sevres near Paris. An atomic standard of mass has not yet been adapted because at present we cannot measure masses on an atomic scale with as great precision as on a macroscopic scale.

An equations must always be dimensionally consistent you can't add apples to oranges.

When a physical quantity is described by a single number. Use the operations of ordinary arithmetic.

A vector quantity has both a magnitude and a direction in space. Combining vector quantities requires a different set of oeprations then scalar quantities.

displacement is simply a change in position of an object which we will assume can be treated as a pointlike particle. Displacement is a vector quantity because we must state not only how far the particle moves, but also in what direction. Walking 3 km north from your front door doesn't get you to the same place a walking 3 km southeast. You will see a displacement written with a letter and an arrow on top of it.