Chapter 1: Describing the Physical Universe

Transcription

1 Chapter 1: Describing the Physical Universe

2 All religions, arts and sciences are branches of the same tree. All these aspirations are directed toward ennobling man's life, lifting it from the sphere of mere physical existence and leading the individual toward freedom. It is no mere chance that our older universities developed from clerical schools. Both churches and universities insofar as they live up to their true function serve the ennoblement of the individual. They seek to fulfill this great task by spreading moral and cultural understanding, renouncing the use of brute force. Albert Einstein, in "Moral Decay" (1937); Later published in Out of My Later Years (1950) 2

3 1.1 What Is Physics? Explain what makes up the universe. Describe how the scientific method is used. Explain the effects of energy on a system. 3

4 What is Physics? Physics is the branch of science traditionally defined as the study of matter, energy, and the relation between them; it was called natural philosophy until the late 19th century and is still known by this name at a few universities. Physics is in some senses the oldest and most basic pure science; its discoveries find applications throughout the natural sciences, since matter and energy are the basic constituents of the natural world. The other sciences are generally more limited in their scope and may be considered branches that have split off from physics to become sciences in their own right. Physics today may be divided loosely into classical physics and modern physics. Encyclopedia.com 4

5 Matter and Energy Mass is a measure of the amount of matter that makes up an object. Matter is anything that has mass and takes up space. Note: you may not always be able to see matter, for example air. [Could you calculate the mass of the air in the classroom? Note the density is 1.2 kg/m 3 ] Energy is an indirectly observed quantity you can t see or touch energy but it gives an indication of the ability of a system to change. There are many forms of energy; light is just one example. 5

6 Systems and Variables We often don t think about it but when we analyze a problem in physics we generally consider a small subset of the universe; we call this subset our system. We might want to discover relationships between several variables in our system, for example, how angle affects speed, or how the mass affects speed. 6

7 The Scale of a System Variables that can be observed and measured directly are on the macroscopic scale. Variables that can be seen, but only with the aid of instruments such as a microscope, are on the microscopic scale. Variables that are on the scale of atoms and are far too small to be observed are on the atomic scale. Many times variables can only be measured indirectly because they are too large or too small. 7

8 Investigating Systems The independent variable is purposefully manipulated (or changed) to see how it affects the dependent variable. You must control other variables to insure a proper cause-and-effect conclusion. The scientific method 1. Ask a question. 2. Formulate a hypothesis. 3. Design a procedure to test the hypothesis. 4. Conduct the experiment and collect the data. 5. Analyze the data. 6. Use the data to make a conclusion. 7. If necessary, refine the question and go through each step again. 8

9 Energy and Systems Energy is a measure of a system s ability to change or create change in other systems. Generally systems tend to go from a higher energy (unstable) to a lower energy level (stable). There are many forms of energy. 9

10 Models A model is an explanation that links the variables in a system through cause and effect relationships. Models are simplified versions of reality. Some examples in physics are how we view atoms and light [sometimes we view light as a particle, and sometimes as a wave!] 10

11 1.2 Distance and Time Express distance measurements in both English and metric units. Measure time intervals in mixed units. Distinguish between independent and dependent variables. Construct graphs. Convert between different units of time. 11

12 Measuring Distance Distance is the amount of space between two points. The length between those two points could be measured in various units such as feet or meters. We will generally use the metric system. 12

13 Standard Prefixes for SI Units Prefix Symbol Factor Factor as Exponent peta P = tera T = giga G = 10 9 mega M = 10 6 kilo k = 10 3 hecto h 100 = 10 2 deca da 10 = 10 1 deci d 0.1 = 10-1 centi c 0.01 = 10-2 milli m = 10-3 micro µ = 10-6 nano n = 10-9 pico p = femto f =

14 Measuring Time There are two ways to think about time: As a moment in time As a time interval In both the English and metric system, the standard unit of time is the second. Can you convert 3 hours, 44 minutes, and 25 seconds into just seconds? 14

15 Experiments involving Time When you want to see how a system changes with time, we generally think of time as the independent variable and graph it on the horizontal axis. 15

16 Distance vs. Time Graphs 16

17 1.3 Speed Define speed. Express an object s speed using various units. Calculate speed, distance, or time given two of the three quantities. List the steps for solving physics problems. 17

18 Calculating Speed The speed of an object is the distance it travels divided by the time it takes to travel that distance. Objects can have a constant speed, or changing speed. The standard unit for speed in the metric system is meters/second. We could also use km/h, mph, ft/sec. 18

19 Speed versus Velocity 19

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21 Solving Motion Problems How far is asking for what? How fast is asking for what? distance speed How long did it take is asking for what? time Look carefully at every number given in the problem unless it s a rare trick question, you will use it. Look at the units attached with each number to help you determine what it is. For example: 5 m, 3 s, 4 m/s. A snake moves 20 meters in 5 seconds. What is the speed of the snake in meters per second? 4 m/s A train is moving at a speed of 50 kilometers per hour. How many hours will it take the train to travel 600 kilometers? 12 hrs 21

22 Chapter 1 Review 1) Scientific theories undergo change. Is this a strength or a weakness of science? Explain. 2) Name a few various forms of energy. 3) What is a system as defined in Chapter 1? What are variables in a system? 4) What is the difference between speed and velocity? 22

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