General Physics Stuff


Important "General Stuff" to know for doing Physics

Discussed below are some definitions, units, and ideas that are central to both Physics and all of science.

1. Uncertainty

Uncertainty is inherent in every measurement or prediction. Any variables in experiments can have uncertainty. The value of the uncertainty depends on the TOOLS you use to measure, and on the QUANTITY that you are measuring. For example, using a meter stick and stop watch to measure a rabbit's velocity might produce a lot of uncertainty in your velocity measurement, but by filming the rabbit with a digital camera and doing video analysis in LoggerPro, you would probably reduce your uncertainty significantly.
2005-09-22-10PM_CDT_Hurricane_Rita_3_day_path.gifHurricane "Cone" Pathways: Great example of a uncertainty

"Scientific knowledge is a body of statements of varying degrees of certainty -- some most unsure, some nearly sure, but none absolutely certain."

Determine Uncertainty
1. Consider your measuring tool
2. Consider your circumstances (conditions)
3. Consider the item you are measuring

A final thought on uncertainty...
Is there proof in science?

In the sense that the word proof is used in math and philosophy, nothing is ever proven in science. There is always some uncertainty about the actual value of results obtained from an experiment. Room for uncertainty should always be left in conclusions and when interpreting or analyzing results.

2. SI Units and the Metric System (Système International d'Unités)

· A system of all units and weights
· The Key agreement of the treaty was signed May 20, 1875
· Adopted by the 11th conference General Conference on Weight and Measures

· Updated by Federal Bureau of Weights and Measures every few years with an international conference

· Base units consistent with metric system

external image metric.gif

Metric Conversion Chart:


3. Problem Solving Format for Physics Problems

Don't let your problem solving format look like this!!!!:
external image moz-screenshot-5.pngexternal image physics-toon.jpg

1. Focus the Problem
2. Describe the Physics
3. Plan the Solution
4. Execute the Plan
5. Evaluate the Solution

Given: Find: Diagram:

Basic Equation: Working Equation:

Solution: Answer:

4. Greek symbols

Alpha Particles (α)

Alpha particles are just helium atoms. Alpha particles consist of 2 protons and 2 neutons, and are not harmful to humans and are not very strong. Alpha particle radiation consists of of helium nuclei and is easily stopped by a sheet of paper.

Beta Particles (β)

Beta particles are high-speed, high-energy electrons, and they are slightly more harmful to humans than alpha particles. Beta radiation consists of electrons and can be stopped by an aluminum plate. The sigma is the greek sign that means net or total. We have used this sign in our equation F=ma, there the sigma stands for the net or total forces applied to an object.

Gamma Rays (γ)

Gamma rays are harmful to humans. They are more harmful than alpha or beta particles. They have very high frequency and short wave lengths.

Sigma (∑)

The sigma is the greek sign that means net or total. We have used this sign in our equation F=ma, there the sigma stands for the net or total forces applied to an object.


5. Theories, Models & Laws

Although in science nothing is really "fact", there are Theories, Models, and Laws to explain what is observed and experimented in the world.

Theory: An all encompassing explanation for why something is true.
Examples: The Big Bang, Einstein's theory of relativity, Evolution
Characteristics of a good theory:

  1. Agrees with data evidence
  2. Makes predictions for future experiments
  3. Simple (based on very few assumptions)
  4. Internal Consistency- there aren't bits and pieces that don't agree

Model: A theory that lacks a single, overarching explanation.
Examples: The Model of the Atom, The Standard Model

Laws: A statement or relationship that is mostly but not necessarily always true.
Examples: F = ma, F = -kx

6. Proportionality

Proportionality is the mathematical relation between two quantities. (if the ratio is constant)

7. % Error

% Error is used in experiments to figure out the percentage of your error between what the actual value of your calculation and what LoggerPro measured as the slope (see force vs. acceleration). This is the formula:

% error = |actual value – measured value| ÷ actual value * 100

8. Getting to Know LoggerPro

Attached is Ms. Wyatt's document (also online) that gives instructions on how to utilize the tools in LoggerPro

LoggerPro is used to collect and analyze data.