An Introduction to Physics Chapter 1-1

What is Physics? Physics is the study of matter, energy and their motion, as well as space and time. Physics is an experimental science. Scientists make observations Develop testable theories Test theories against new observations

In the beginning… Physics is the oldest of all academic disciplines. Astronomers were the first physicists. Early Astronomers were not experimental scientists. Would think about there observations and develop reasonable explanations that fit the data. Not very good at predicting the outcome of events.

Areas of Physics Mechanics- Motion and its causes Thermodynamics- Heat and Temperature Vibrations- Repetitive Motion Optics- Light Electromagnetism- Electricity, Magnetism, and Light Relativity- Particles moving at high speeds Quantum Mechanics- Behavior of tiny particles

The Scientific Method 1.Make observations and collect data that leads to a question (How/Why?) 2.Formulate testable explanation(s) to fit that data. 3.Design and perform experiment to test explanation(s) 4.Interpret results of experiment and revise explanation(s) if necessary. 5.State conclusion in a way that can be evaluated by others.

Models The subject matter covered by physics is very complex. Physicists often use simple models to explain the most fundamental aspects of a situation. We often neglect variables that affect the situation only slightly but make calculations very difficult. In spite of these simplifications we can still make rather accurate predictions about various situations.

Models (cont) Models help develop explanations. Galileo performed a ‘thought experiment’ that enabled him to disprove the notion that heavier object fall faster than lighter ones. He imagined two equal bricks falling together. They must fall at the same rate. He then imagined the same two bricks falling but they were tied together, would they fall any faster?

Models and Experiments Galileo had no way of measuring the speed of falling objects. He used a model of a ball rolling down a ramp to model the act of falling, the steeper the ramp the closer the model represented the actual situation.

Measurements in Experiments Chapter 1-2

Numbers as Measurements Measurements in Physics require more than just numbers. Each measurement will be associated with a quantity as well as what kind of quantity is being measured, referred to as a dimension. There are 3 dimensions we talk a lot about in physics Distance Mass Time

Standards of Measurement So everyone can understand values that are reported from an experiment, all scientists must use the same standard of measure. SI is the standard for science. Distance: Meter = Distance traveled by light in a vacuum in 3.3 x seconds. Mass: Kilogram = Mass of 1 Liter of Water Time: Second = 9,192,631,700 times the period of radio wave emitted from a cesium-133 atom.

A Wide Range Physicists deal with the wide range of numbers using two methods Prefixes are used to change the units. Ex. 1 meter = 1000 millimeters Scientific notation also helps to make small or large numbers more manageable.

Scientific Notation To convert a number into scientific notation. Move the decimal place so there is only 1 digit to the left of the decimal. Count the number of places the decimal moved. That number becomes the exponent on the 10. IF the number is less than one the exponent will be negative. (if the decimal moves to the left) To enter into a calculator use the EE button.

Accuracy vs Precision Accuracy is how closely a measurement agrees with the true value. Precision is how exact or refined the measurement is. (How repeatable is the measure?)

Problems with Accuracy Problems with accuracy are usually due to error. It can be caused by having un-calibrated or poorly calibrated measuring devices. Also human error can lead to inaccurate measurements.

Problems with Precision Problems in precision generally are a result of the limitations of the measuring device. When measuring in science we always estimate the next decimal place Imprecise measurements are dealt with in science using Significant Figures If a mountain’s height is known to the nearest 5m then would adding a 1 meter pile of rocks at the top change its height?

Significant Figures (SigFigs) When doing calculations in physics we will always report the answer to have the same number of sigfigs as the value in our calculations with the least number of sigfigs.

What are SigFigs? All non-zero numbers. Some zeros are also sigfigs. Zeros between nonzero digits are significant Zeros to the left of nonzero numbers are not significant Zeros at the end of a number and to the right of a decimal are significant Zeros at the end of a number and to the left of the decimal are only significant if you have made the measurement. tmlhttp://science.widener.edu/svb/tutorial/sigfigures.h tml

Dimensional Analysis Most of the problems you will face in physics ask you to take information you have and ask you for information you don’t have, usually of another unit or dimension. Conversion factors can be used to get this information as long as you properly align the factors so the units cancel (or divide out) Dimensional Analysis uses a series of fractions to convert your given information to the information that was requested

How many seconds are in a Day? While you may not have this figure memorized, you can use information you do have to find out. Step 1. Determine the units of the answer. if you want to know how many seconds are in a day you want sec/day. Step 2. Determine factors that you already know, or are given by the problem. You know that there are 24 hrs/day, 60min/hour, 60 sec/minute.

Sec/Day (cont) Step 3. If you align these figures properly the units will cancel and you will be left with sec/day. Keep in mind that all of the fractions we just listed can be inverted (1day/24hours)