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

2. 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.

3. 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.

4. 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.

5. Models
Click below to watch the Visual Concept.
Visual Concept

6. 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).

7. 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.

8. 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.

9. 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.

10. 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.

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

12. 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.

13. Converting Units
Build a conversion factor from the previous table. Set it up so that units cancel properly.
Example - Convert 2.5 kg into g.
Build the conversion factor:
This conversion factor is equivalent to 1.
103 g is equal to 1 kg
Multiply by the conversion factor. The units of kg cancel and the answer is 2500 g.
Try converting
.025 g into mg
.22 km into cm
When presenting the example, you may wish to ask students for the conversion factor before you show it. Be sure students know that they must set up the conversion factor such that the units cancel properly. To discuss this issue, ask students how we know that the conversion factor is 103 g /1 kg rather than 1 kg /103 g.
Answers: 0.25 g = 250 mg, 0.22 km = 22,000 cm. Note that the second problem requires two conversions (if using the table), first km into m, and then m into cm.

14. Classroom Practice Problem
If a woman has a mass of mg, what is her mass in grams and in kilograms?
Answer: 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.

15. Accuracy and Precision
Precision is the degree of exactness for a measurement.
It is a property of the instrument used.
The length of the pencil can be estimated to tenths of centimeters.
Accuracy is how close the measurement is to the correct value.

16. 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.

17. Measurement of Parallax
Click below to watch the Visual Concept.
Visual Concept

18. Significant Figures
Significant figures are the method used to indicate the precision of your measurements.
Significant figures are those digits that are known with certainty plus the first digit that is uncertain.
If you know the distance from your home to school is between 12.0 and 13.0 miles, you might say the distance is 12.5 miles.
The first two digits (1 and 2) are certain and the last digit (5) is uncertain.

19. Rules for Determining Significant Zeros
Click below to watch the Visual Concept.
Visual Concept

20. Counting Significant Figures
Examples
50.3 m s
0.892 kg ms
57.00 g kg
1000 m
20 m
Scientific notation simplifies counting significant figures.
Have students read the rule and then apply it to the two measurements to the right. (Each rule has two examples.) Give them some time to read the rules and try on their own to apply the rules. Then go over the answers with them (below) so they can see where they made mistakes.
Answers: three, five, three, one, four, seven, one, one
This activity also provides an opportunity to show them that converting the above numbers to different units does not affect the number of significant figures. For example, converting kg into 892 g still yields three significant figures. Also show them that converting g into kg yields kg and not kg because the number must still have 4 significant figures. The zeros at the end are measured values and cannot be ignored.

21. Rules for Rounding Numbers
Click below to watch the Visual Concept.
Visual Concept

22. Rounding Round to 3 figures: 30.24 32.25 32.65000 22.49 54.7511 54.75
Have students practice rounding answers to the correct number of significant figures (three in this case).
Answers: 30.2, 32.3, 32.6, 22.5, 54.8, 54.8, 79.4

23. Calculating with Significant Figures
123 x 5.35
Have students apply the rule to the sample. (Answers are below.) Remind them often that “calculators do not keep track of significant figures.” Some students simply write down every digit they see on their calculator or round off in some arbitrary way. Students are very reluctant to take an answer such as 2540 m and round it off to 2500 m in order to get just 2 significant figures that the problem might require. However, many will simply take a number like m and call it 0.08 m even though the problem might require three significant figures in the answer.
Answers: 103.2, 658

24. 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.

25. 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.

26. 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?

27. 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 = s.
The graph could also be extended.
This allows predictions for points beyond s.

28. Shapes of Graphs and Mathematical Relationships
Click below to watch the Visual Concept.
Visual Concept

29. 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.

30. Dimensional Analysis
Dimensions can be treated as algebraic quantities.
They must be the same on each side of the equality.
Using the equation y = (4.9)t2 , what dimensions must the 4.9 have in order to be consistent?
Answer: length/time2 (because y is a length and t is a time)
In SI units, it would be 4.9 m/s2 .
Always use and check units for consistency.
It is important to stress the use of units at all times. Discuss the example in the text showing the calculation of the time required when the speed is given in km/h and the distance traveled is given in km.
You could also discuss quantities such as density in g/cm3 or tire pressure in lb/in2 to show them that you can often deduce the equation from the units. (For instance, the equation for density is D = m/V, because g is a measure of m and cm3 is a measure of V.)
However, be sure to show students that unit analysis does not always yield the correct equation. Tell them that the units for acceleration are m/s2 and ask them to write an equation. They will probably come up with (a = d/t 2) and this is not a correct equation. Try rewriting the units of m/s2 as (m/s)/s and see what they come up with for an equation.

31. Order of magnitude Rounds to the nearest power of 10
The number 65 has an order of magnitude of 102 because it is closer to 102 than to 101
What is the order of magnitude for 4200, and
6.2 x 1023?
Answers: 103, 10-1 , and 1024
Allows you to get approximate answers for calculations
Showing each number on a power of ten number line (10-3, 10-2, ……, 103) might help students decide the order of magnitude for the three numbers shown.
Orders of magnitude can be used to check the “believability” of an answer. Calculator errors such as multiplying instead of dividing or forgetting to use parentheses when required can lead to very unrealistic answers. Students should be trained to look at an answer and ask themselves if it could possibly be true. Sometimes their lack of experience prevents this, but it is a good habit to begin to develop.

32. 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.