Preview Section 1 What Is Physics? Section 2 Measurements in Experiments Section 3 The Language of Physics

What do you think? What are some topics you expect to study this year in physics? The principles of physics govern our everyday lives. Do you know any of the laws of physics? If so, describe the law or rule of physics as you understand it. Do the laws of physics ever change? When asking students to express their ideas, you might try one of the following methods. (1) You could ask them to write their answers in their notebook and then discuss them. (2) You could ask them to first write their ideas and then share them with a small group of 3 or 4 students. At that time you can have each group present their consensus idea. This can be facilitated with the use of whiteboards for the groups. The most important aspect of eliciting student’s ideas is the acceptance of all ideas as valid. Do not correct or judge them. You might want to ask questions to help clarify their answers. You do not want to discourage students from thinking about these questions and just waiting for the correct answer from the teacher. Thank them for sharing their ideas. Misconceptions are common and can be dealt with if they are first expressed in writing and orally. Spend as much or as little time as you want on this introductory slide. It would be interesting to hear some ideas about the laws of physics. Encourage them to explain their beliefs regarding motion, electricity, or any of the many other topics covered in physics.

Allow students to see the many topics covered in physics Allow students to see the many topics covered in physics. You may want to discuss which topics your course will focus on.

Scientific Method Models are often used to explain the principles of physics. Systems are defined to study the important components. All experiments must be “controlled.” Limit the experiment to testing one factor at a time. Tell students we define systems to eliminate the unimportant factors. For example, when a bat strikes a ball, we do not worry about the air or the color of the bat. Ask students to explain why it is important to control experiments by testing a single factor at a time.

Models Click below to watch the Visual Concept. Visual Concept

Hypotheses A hypothesis is a reasonable explanation for observations. Before Galileo, scientists believed heavy objects fell more rapidly than light objects. Galileo considered the situation shown. If the heavy brick falls faster, what would happen if they were tied together? Ask students to explain what they believe would happen to the two-brick system. Galileo said it should fall slower than the heavy brick because the lighter brick would slow down the heavy brick (Picture b). But, he also said it should fall faster then the heavy brick because two bricks combined are heavier and heavy objects fall faster (Picture c).

Galileo’s Hypothesis Since the two bricks can’t fall faster and slower than the heavy brick, Galileo concluded the original hypothesis was wrong. Galileo’s hypothesis: All objects fall at the same rate in the absence of air resistance. Galileo made predictions based on this hypothesis and tested it extensively. Testing hypotheses is the basis of all science.

Now what do you think? What are some topics you expect to study this year in physics? How do scientists discover the laws of physics? Do the laws of physics ever change? The understanding that science is an evolving field of knowledge rather than a static set of facts can help generate student interest in science. Use the example of Galileo’s hypothesis to initiate a discussion on the scientific method. Scientists develop and test hypotheses to discover new theories or laws, or to modify existing theories. Thus, the set of established physical laws and theories changes over time as hypotheses are tested and revised. See if students can suggest examples of theories or laws that have evolved. Examples you may wish to discuss include the development of atomic theory and the relativity of space and time.

What do you think? What system of measurement is used in physics? Is a measurement of 2 cm different from one of 2.00 cm? If so, how? What is the area of a strip of paper measuring 97.3 cm x 5.85 cm? How much should you round off your answer? When asking students to express their ideas, you might try one of the following methods. (1) You could ask them to write their answers in their notebook and then discuss them. (2) You could ask them to first write their ideas and then share them with a small group of 3 or 4 students. At that time you can have each group present their consensus idea. This can be facilitated with the use of whiteboards for the groups. The most important aspect of eliciting student’s ideas is the acceptance of all ideas as valid. Do not correct or judge them. You might want to ask questions to help clarify their answers. You do not want to discourage students from thinking about these questions and just waiting for the correct answer from the teacher. Thank them for sharing their ideas. Misconceptions are common and can be dealt with if they are first expressed in writing and orally.

Measurements Dimension - the kind of physical quantity being measured Examples: length, mass, time, volume, and so on Each dimension is measured in specific units. meters, kilograms, seconds, liters, and so on Derived units are combinations of other units. m/s, kg/m3, and many others Scientists use the SI system of measurement. Ask students to suggest other examples of dimensions, specific units, and derived units. You may also want to discuss the advantages of using a common system of measurement.

This chart allows students to see the original standard and the current standard.

Prefixes It might be a good time to let students know which prefixes are more commonly seen, such as micro through mega. They will need to know these in order to convert units.

Chapter 1 Sample Problem Section 2 Measurements in Experiments Chapter 1 Sample Problem A typical bacterium has a mass of about 2.0 fg. Express this measurement in terms of grams and kilograms. Given: mass = 2.0 fg Unknown: mass = ? g mass = ? kg

Sample Problem, continued Section 2 Measurements in Experiments Chapter 1 Sample Problem, continued Build conversion factors from the relationships given in Table 3 of the textbook. Two possibilities are: Only the first one will cancel the units of femtograms to give units of grams.

Sample Problem, continued Section 2 Measurements in Experiments Chapter 1 Sample Problem, continued Take the previous answer, and use a similar process to cancel the units of grams to give units of kilograms.

Accuracy and Precision Section 2 Measurements in Experiments Chapter 1 Accuracy and Precision Accuracy is a description of how close a measurement is to the correct or accepted value of the quantity measured. Precision is the degree of exactness of a measurement. A numeric measure of confidence in a measurement or result is known as uncertainty. A lower uncertainty indicates greater confidence.

Classroom Practice Problem If a woman has a mass of 60 000 000 mg, what is her mass in grams and in kilograms? Answer: 60 000 g or 60 kg Show students how to get the conversion factor using the table (1 g / 1000 mg). The reverse (1000 mg / 1 g) will not work because the mg will not cancel out. Similarly, they need to find the conversion from g into kg. In order to make the grams cancel, the conversion factor is 1 kg / 1000 g.

Errors in Measurement Instrument error Method error Instrument error is caused by using measurement instruments that are flawed in some way. Instruments generally have stated accuracies such as “accurate to within 1%.” Method error Method error is caused by poor techniques (see picture below). Point out to students the necessity of making sure your line of sight is directly over the measurement. Discuss measurement methods that improve precision and accuracy, such as: -not using the end of the meter stick (as was done in the picture on the last slide) -measuring a quantity several times and averaging the results -having different people measure the same quantity and averaging the results.

Now what do you think? What system of measurement is used in physics? Is a measurement of 2 cm different from one of 2.00 cm? If so, how? What is the area of a strip of paper measuring 97.3 cm x 5.85 cm? How much should you round off your answer? Have students revisit the opening questions. They should now be able to answer as follows: -Physics uses the SI system of measurement. -A measurement of 2 cm is different from a measurement of 2.00 cm. The latter has three significant figures and is more precise than a measurement of 2 cm, which has just one significant figure. -The area should be rounded to three significant figures, 569 cm2.

What do you think? What different ways can you organize data so that it can be analyzed for the purpose of making testable predictions? When asking students to express their ideas, you might try one of the following methods. (1) You could ask them to write their answers in their notebook and then discuss them. (2) You could ask them to first write their ideas and then share them with a small group of 3 or 4 students. At that time you can have each group present their consensus idea. This can be facilitated with the use of whiteboards for the groups. The most important aspect of eliciting student’s ideas is the acceptance of all ideas as valid. Do not correct or judge them. You might want to ask questions to help clarify their answers. You do not want to discourage students from thinking about these questions and just waiting for the correct answer from the teacher. Thank them for sharing their ideas. Misconceptions are common and can be dealt with if they are first expressed in writing and orally. Hopefully, students will think about data tables, graphs, equations, and drawings or diagrams. Try having a discussion about which method is most useful or does each have value in different situations. You might get them to discuss graphs or equations or diagrams they have used in previous science classes.

Tables This table organizes data for two falling balls (golf and tennis) that were dropped in a vacuum. (This is shown in Figure 13 in your book). Can you see patterns in the data?

Graphs Data from the previous table is graphed. A smooth curve connects the data points. This allows predictions for points between data points such as t = 0.220 s. The graph could also be extended. This allows predictions for points beyond 0.400 s.

Equations Show relationships between variables Directly proportional Inversely proportional Inverse, square relationships Describe the model in mathematical terms The equation for the previous graph can be shown as y = (4.9)t2. Allow you to solve for unknown quantities Show students a direct relationship such as distance and velocity in v = d/t. Then use this same equation to show the inverse relationship between velocity and time.

Now what do you think? What different ways can you organize data so that it can be analyzed for the purpose of making testable predictions? See if students now have anything to add to their lists from the beginning of the presentation. At this point, they should recognize that each method is useful, and that the preferred method depends on the situation. Ask students to describe the advantages of different types of data organization that have been covered in the presentation (data tables, graphs, equations). Also have them brainstorm situations in which diagrams would be useful.

Chapter 1 Extended Response Standardized Test Prep Extended Response 16. You have decided to test the effects of four different garden fertilizers by applying them to four separate rows of vegetables. What factors should you control? How could you measure the results?

Chapter 1 Extended Response Standardized Test Prep Extended Response 16. You have decided to test the effects of four different garden fertilizers by applying them to four separate rows of vegetables. What factors should you control? How could you measure the results? Sample answer: Because the type of fertilizer is the variable being tested, all other factors should be controlled, including the type of vegetable, the amount of water, and the amount of sunshine. A fifth row with no fertilizer could be used as the control group. Results could be measured by size, quantity, appearance, and taste.

Extended Response, continued Chapter 1 Standardized Test Prep Extended Response, continued 17. In a paragraph, describe how you could estimate the number of blades of grass on a football field.

Extended Response, continued Chapter 1 Standardized Test Prep Extended Response, continued 17. In a paragraph, describe how you could estimate the number of blades of grass on a football field. Answer: Paragraphs should describe a process similar to the following: First, you could count the number of blades of grass in a small area, such as a 10 cm by 10 cm square. You would round this to the nearest order of magnitude, then multiply by the number of such squares along the length of the field, and then multiply again by the approximate number of such squares along the width of the field.