PhysicsChapter 1

Saul BeltranMr. Kim12/9/05 Per. 7

A Summary

Physics, like other sciences, is a creative endeavor. It is not simply a collection of facts. Important theories are created with the idea of explaining observations. To be accepted, theories are tested by comparing their predictions with the results of actual experiments.

Models and Theories

• Scientists often devise models of physical phenomena.

• A model is a kind of picture or analogy that seems to explain the phenomena.

• A theory is usually deeper and more complex that 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 and Units

• Measurements play a crucial role in physics, but can never be perfectly precise. It is important to specify the uncertainty of a measure either by stating it directly using the ± notation, and/or by keeping only the correct number of significant figures.

• The number of reliably known digits in a number is called the number of significant figures. (Example: 202 has three significant figures, but 200 only has one significant figures. Reason: when the zero is in between two numbers it is important, otherwise it is not. )

Measures and Unites Continued

• Physical quantities are always specified relative to a particular standard or unit.

• The unit used should always be stated.• The commonly accepted set of units today is the System

International (SI), in which the standard units of length, mass, and time are 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.

Important Information

Length (or distance)

Meters (approximate)

Neutron or proton (radius)

10٨(-15) m

Atom 10٨(-10) m

Virus 10٨(-7) m

Sheet of paper 10٨ (-4) m

Finger width 10٨(-2) m

Football field length 10٨(2) m

Mt. Everest height 10٨4 m

Earth diameter 10٨7 m

Earth to Sun 10٨11m

Nearest star, distance

10٨16 m

Nearest Galaxy 10٨22 m

Farthest Galaxy visible

10٨26 m

Some Typical Time Intervals and Masses

Time Interval Seconds

Lifetime of very unstable particle

10٨23s

Lifetime of radioactive elements

10٨22s to 10٨28s

Lifetime of muon 10٨-6s

Time between human heartbeats

10٨0s

One day 10٨5s

One year 3x10٨7s

Human life span 2x10٨9s

Length of recorded history

10٨11s

Humans on Earth 10٨14s

Life on Earth 10٨17s

Age of Universe 10٨18s

Object Kilogram

Electron 10٨-30 kg

Proton, neutron 10 ٨-27 kg

DNA molecule 10 ٨-17 kg

Bacterium 10 ٨-15 kg

Mosquito 10 ٨-5 kg

Plum 10 ٨-1kg

Person 10 ٨2 kg

Ship 10 ٨8 kg

Earth 6x10 ٨24kg

Sun 2x10 ٨30 kg

Galaxy 10 ٨41 kg

Metric (SI) PrefixesPrefix Abbreviation Value

Exa E 10 ٨18

Peta P 10 ٨15

Tera T 10 ٨12

Giga G 10 ٨9

Mega M 10 ٨6

Kilo K 10 ٨3

Hecto H 10 ٨2

Deca Da 10 ٨1

Deci D 10 ٨-1

Centi C 10 ٨-2

Milli M 10 ٨-3

Micro u 10 ٨-6

Nano N 10 ٨-9

Pico P 10 ٨-12

Femto F 10 ٨ -15

Atto A 10 ٨-18

The End?

Thank you for listing to this presentation. If you are still reading this, then you have too much time because you are interested in physics. Now get ready for the test suckers.

Quiz

http://www.homework55.com/physics/ph8-16-05/Significant%20Figures.htm