1 / 44

Chapter 1 The Science of Physics

Chapter 1 The Science of Physics. 1.1 What is Physics. The Topics of Physics Many people consider Physics to be a difficult science far removed from their lives. Its true, physicists do study things about the universe and particles smaller than atoms.

jeffersonn
Download Presentation

Chapter 1 The Science of Physics

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Chapter 1The Science of Physics

  2. 1.1 What is Physics The Topics of Physics • Many people consider Physics to be a difficult science far removed from their lives. • Its true, physicists do study things about the universe and particles smaller than atoms. • However, everyday things around you can be described by the tools of physics. • The goal of physics is to use a small number of basic concepts, equations, and assumptions to describe the physical world and make predictions.

  3. Physics discoveries often turn out to have unexpected practical applications and advances in technology. These can lead then to new physical discoveries. • This car shows how the areas of physics apply to an operating vehicle.

  4. Physics is Everywhere • People know more about physics than they realize. • Most of us know if you do not keep ice cream in the freezer it melts. • If you throw things, you expect them to fall. • People who design sailboats have a working knowledge of fluid dynamics. They understand that water can produce a lot of resistance. Video

  5. When scientists look at the world they see a network of rules and relationships that will happen in a given situation. • Everything we will study in this course was learned by someone who looked out at the world and questioned how thinks worked. • There is no exact procedure scientists follow in their research. However, there are some common steps most follow - known as the scientific method.

  6. Physics uses models that describe phenomena • Physicists often use models to describe nature. • When developing a model, physicists must decide which parts of the phenomenon are relevant and what to discard. • When throwing a ball, observations can include; its path, diameter, spin, air density, and mass of the object. • A computer simulation or scale replicas are also used to study situations and predict results. Video

  7. Models can help build hypotheses • A scientific hypotheses is a reasonable explanation for an observation – one that can be tested with additional experiments. • In 1638, Galileo proposed the following thought experiment. Because people felt heavier objects fell faster than lighter ones he proposed the following… (a) heavier falls faster (b) heavier pulls lighter down faster (c) lighter will slow faster (d) all objects must fall at the same rate Video

  8. Models help guide experimental designs • Galileo performed many experiments to test his hypotheses. • To be certain that he was observing differences due to weight only, he used objects that were the same size. Plus he made sure they were all dropped from the same height. • Testing done in this way are considered controlled experiments. When only one variable is changed at a time with multiple trials. • In Galileo’s time, air resistance was an issue he could not resolve but he was certainly on the right track using the scientific method correctly. *Galileo used the tower of Pisa in 1589 Video

  9. Questions1. T / F Physics discoveries often turn out to have unexpected practical applications and advances in technology. 2. There is no single procedure that scientists follow in their work. However there are some common steps most follow known as the scientific _______.3. ______ is the area in physics that studies light.4. When developing a _____, physicists must decide which parts of the phenomenon are relevant and what to discard.5. A scientific __________ is a reasonable explanation for observation – one that can be tested with additional experiments. true method Optics model hypotheses

  10. 1.2 Measurements in Experiments Numbers As Measurements • Scientists perform experiments to test hypotheses about how changing one variable in a situation affects another. • In science, measurements are more than just a number. • We need to know what dimension is being measured – length, mass, time?

  11. We also need to know what units – meters, feet, miles, light years? • What kind of physical quantity is represented by the measurement – force, velocity, degrees, or energy?

  12. SI is the standard measurement system for science • Systeme International d’ Unites or SI for short is more commonly known to us as the metric system. • We know some of these units as the meter, kilogram, liter, and second. • As we get more involved in physics we will learn derived units like meters per second for velocity and kilogram m/s2 for newtons of force. • The metric system became popular world wide because it did not rely on a mess of separate standards, and it use a decimal system rather than fractions.

  13. Length is measured in meters • In the metric system, length is measured using the meter. • Compared to a 36 inch ruler, the meter is about 39 inches in length. • The meter stick is divided into… • 1 meter (m) • 10 decimeters (dm) • 100 centimeters (cm) • 1000 millimeters (mm)

  14. Measuring • About how long is this blue line in mm? Answer Time for you to practice on your own. Measure the 10 lines in your packet. 100 mm

  15. Measuring in centimeters • About how long is this blue line in cm? Answer Time again to measure on your own 10 cm

  16. Measuring in decimeters • About how long is this blue line in dm? Answer Time again to measure on your own 1 dm

  17. Measuring in meters • About how long is this blue line in meters? Answer Time again to measure on your own 0.1 m

  18. Lets measure from here to the bus stop on Sierra Hwy. • How many meter sticks would it take? Answer • The word kilo means 1000, so 1000 meter is known as a kilometer. • 100 kilometers is about 62 statute miles. 1000

  19. Measuring liquids or volume • The unit of measurement for volume is the liter. A liter is about the size of a quart. • Four liters is close in volume to the gallon. • Where does the liter come from? • Consider a 10 cm x 10 cm x 10 cm cube.

  20. To summarize volume, a litter is 10 cm x 10 cm x 10 cm = 1000 cm3 • A milliliter (ml) is 1cm x 1cm x 1cm or one cubic centimeter “cc” • Therefore; 1000 ml would fit inside your 1 liter paper cube.

  21. Mass • The gram (g) is usually our standard unit. • One gram weighs about the same as two paper clips. • If we want to measure heavier objects we use the kilogram (kg). • In Physics, we always use the kilogram. • Your science book weighs about 2 kg. • If you weigh about 110 pounds, that is the same as 50 kg.

  22. How volume and mass are related • We know that 1000 ml of water is the same as one liter (l). • How much does one liter of water weigh? • The answer is … one kilogram. • Therefore, one cubic centimeter of water would weigh one gram. • If we were to add 50 ml of water to an empty flask, weigh it again, it would now weigh 50 grams more.

  23. Measuring Temperature • The temperature of this room does not change if we measure it using the Fahrenheit scale or the Celsius scale. • Water freezes at 32o degrees Fahrenheit (F) and 0o degrees Celsius (C). • Water boils at 212o F and 100o C. • Our classroom is about 75o F or 24o C.

  24. The metric system is based on powers of 10. • The following table shows common prefixes based on their power.

  25. Convert the following to scientific notation 0.123  123  .00005  50000  1.23 x 10-1 1.23 x 102 5 x 10-5 5 x 104

  26. Complete the following calculations (3.0 X 105)(5.0 X 103) = (2.0 X 105)(16.0 X 10-7) = (4.8 X 107)/(1.2 X 103) = (4.28 X 102)/(2.14 X 10-7) = 15 x 108 3.2 x 10-1 4.0 x 104 2.00 x 109

  27. Practice A Metric Prefixes • A typical bacterium has a mass of about 2.0 femtograms (1 x 10-15 g). Express this measurement in terms of grams and kilograms. • Lets do grams first… • For kilograms, remember 1000 g = 1 kg, so 1 kg = 1 x 103 g… 2.0 x 10-15 g 2.0 x 10-18 kg

  28. Accuracy And Precision • All measurements have a degree of uncertainty, therefore error in experiments must be minimized. • If measurements are taken using one method and some are taken using another, we can get method error. • This can be reduced by using standardized measuring techniques. If you and your lab partner are looking at different angles while reading a ruler, this could cause errors. • Instrument error can be caused by using broken or un-calibrated equipment.

  29. Precision describes the limitations of the measuring equipment • Poor accuracy involves errors that can often be corrected. • Precision describes how exact a measurement can be. For example, a measurement of 1.325 m is more precise than one of 1.3 m. • A lack of precision is usually due to the limits of the equipment being used. A ruler showing only centimeters and no millimeters could limit the user’s precision.

  30. Significant figures help keep track of imprecision • A common convention used in science to indicate precision is known as significant figures. • In the case of the measurement of the pencil as about 18.2 cm, the measurement has three significant figures. • Because the ruler shown here does not show millimeters, we have to estimate the 0.2. • The actual value is some where between 18.15 and 18.25 cm. • When the last digit is a zero, it is difficult to tell whether the zero is a place holder or significant.

  31. Significant figures in calculations require special rules • In calculations, the number of significant figures in your result depends on the number of significant figures in each measurement. • If we measure a mountain to be 1710 m high, we have three significant figures only. Then adding a 0.20 m pile of rocks on top does not change our measure significantly. We can not just assume the mountain is now 1710.2 m high now. • The final value can not be more precise than what we started with.

  32. The following are rules to determine whether zeros are significant or just place holders. • Our text book considers any zeros right of a number not to be significant but some books do.

  33. When multiplying two values like 4.6 and 6.7, you get 30.82. However, each of your starting values only had two significant figures. • Therefore, your answer should only have two as well and be rounded to 31. • In addition or subtraction, you round to the least value right of the decimal point.

  34. If numbers end in a 5, only round up if the number before is odd. • Remember “odd” up! Video

  35. Questions1. How many decimeters in a meter?2. How many grams in a kilogram?3. Is this showing high accuracy or high precision?4. In the number 200.4, how many significant figures?5. What final value should we have If the number 123.45 is rounded to 4 significant figures? 10 1000 _______ 4 123.4

  36. 1.3 The Language of Physics Mathematics and Physics • Physicists create simple models to better understand the world. • They use mathematics to analyze, see relationships, and predict what might happen. • Earlier we looked at Galileo’s observations of falling objects. This table shows the data from two objects falling in a vacuum.

  37. When a scientist looks at data like this they find it easier to graph the results to see any patterns. • In this case we see an obvious relationship between time and distance. • The mathematical relationship here is that the distance each object falls equals 4.9 x (time of fall in seconds)2

  38. Physics equations describe relationships • The physics equation is a compact statement based on a model of the situation. • To make expressions as simple as possible, physicists often use letters to describe specific quantities in an equation. • For example, “v” could stand for velocity. The Greek letter ∆ (delta) is used to represent change. • The symbol ∑ (sigma) is used for “sum” or “total”. • The formula that would represent the acceleration graph from the previous slide would look like this…

  39. Lets review how we can combine units of quantity. • If we combine these units, kg (m/s) (1/s) we will get the following… kg * m/s2 • What will we get by combining these units, (kg/s) (m/s2)… answer • One more example, (kg*/s) (m/s)2… answer kg * m/s3 kg * m2/s3

  40. Evaluating Physics Equations • Dimensional analysis makes use of the fact that dimensions can be treated as algebraic quantities. • For example, quantities can be added or subtracted only if they have the same dimensions. • If a car is moving at 88 km/h this measurement is given in the dimension of length over time. • How long would it take our car to travel 725 km?

  41. Order of magnitude estimations check answers • An order-of-magnitude calculation can help you find the power of 10 that is closest to your answer. • In the last problem we were traveling a distance of 725 km. We could round that to 1000 km or 1 x 103 km. And 88 km would become 1 x 102 km/h. • By eliminating km units here, we get our final answer -close to the actual value of 8.2 h.

  42. Lets estimate how much gasoline is used by automobiles each year in the United States. • If we round the number of people in the U.S. to 300 million and assume there are 2 autos for every 5 people, that equals 120 million autos. • If the average miles driven per year are 10,000 and each auto averages 20 miles per gallon, then each car uses about 500 gal/year. • The final set up looks like this…

  43. Questions1. To make expressions as simple as possible, physicists often use ______ and Greek symbols to describe specific quantities in an equation.2. The symbol ∑ (sigma) is used for sum or ____ .3. If we combine these units, (kg/s) (m/s) we will get the following…4. An order-of-magnitude calculation can help you find the power of ___ that is closest to your answer.5. If a car can travel 10 km per every liter of gasoline used, how many liters will it use in 40 km? letters total kg * m/s2 10 4 gal

  44. End

More Related