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Chapter 2

Chapter 2. Milbank High School The Science of Physics Measurements Vocabulary. Ammann. Matter, Energy, & Ideas. Matter: Something that occupies space and has mass. Energy: The ability to do work. Law of Conservation of Energy and Matter: Energy and Matter are neither created nor

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Chapter 2

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  1. Chapter 2 Milbank High School The Science of Physics Measurements Vocabulary Ammann

  2. Matter, Energy, & Ideas Matter: Something that occupies space and has mass. Energy: The ability to do work. Law of Conservation of Energy and Matter: Energy and Matter are neither created nor destroyed but only changed in form. Matter and Energy are interchangeable: E = mc2 Hypothesis-- Scientific Guess. Theory-- An idea with much supporting evidence. Law or Principle-- It's proved. No exceptions.

  3. Observations Subjective observation(qualitative)--depends upon opinion. Examples: It's hot in here. He’s a Shorty. Optical Illusions fool the eye. Objective observation(quantitative)-- is measured. It is factual. Examples: It's 22oC in here. He’s 1.7 meters tall. He's 94 cm around.

  4. Measurement Since the formal practice of Science began, Scientists have needed a definite way to both record and share their findings with the world

  5. Early measurements troubled by inconsistencies • Cubits, fathoms, the foot were all used to measure lengths • Scientists from around the world agreed that a single set of units were needed • The System International (SI) was formed • Based on the metric system

  6. Fundamental Units of the SI system

  7. You need to use UNITS! • Without units numbers are meaningless, from this point any numbers should be appropriately “dressed” with the proper units. • We will use the “MKS“ System • Meter, Kilogram, Seconds • Do not use the “CGS” System • Centimeter, Gram, Seconds

  8. Mass • The measure of how much material an object is made of. • It is also a measure of the inertia, the resistance force to a change on motion. • Mass is often confused with weight, the force of attraction with the earth. • An object in space has the same mass, but changes to zero weight units!

  9. Objects in the MKS system • Telephone • Length of hand set cord : 1 meter • Mass : 1 Kilogram • Duration of one ring : 1 second • Car • Length of the Car : 5 meters • Mass : 1000 KG • Duration of 0 to 60 MPH: 6.2 second

  10. Common English to Metric conversions • 1 centimeter = 0.394 inches • 1 inch = 2.54 centimeters • 1.0 slug)g = weight (mixed mass units) • (1.0 slug) (32.174 ft/s2) = 32.174 poundsI.e., 1.0 slug (mass) is equivalent to 32.174 pounds (weight • 1 pound (lb) = .45 kg • 1 kg = 2.2 pounds (lb)

  11. Summary • The meter, second, and kilograms are SI base units of length, time, and mass • Fundamental units can be combined mathematically to form DERIVED units. • Prefixes are used to change SI units by powers of 10 • The international system of units (SI) allows scientists and engineers to exchange data • MKS units use kilograms instead of grams and meters instead of centimeters, both CGS and MKS use seconds for time units

  12. Metric Prefixes

  13. Significant Digits What are they? And How do you use them?

  14. Accuracy: • This is the concept which deals with whether a measurement is correct when compared to the known value or standard for that particular measurement. • When a statement about accuracy is made, it often involves a statement about percent error. • Percent error is often expressed by the following equation: • % error = (|experiment value - accepted value| / accepted value) x 100% • Also see Problem Set # 1-14 in the workbook

  15. Precision: • This is the concept which addresses the degree of exactness when expressing a particular measurement. • The precision of any single measurement that is made by an observer is limited by how precise the tool (measuring instrument) is in terms of its smallest unit. • How would you divide the following 1 meter long bar up into smaller divisions? Why? What would your choice have to do with precision? 1 METER BAR

  16. Precision and Measuring:

  17. Significant Digits: • When someone else has made a measurement, you have no control over the choice of the measuring tool or the degree of precision associated with the device used. • You must rely on a set of rules to tell you the degree of precision. • Refer to the “Rules for determining when zeros are significant” (PS#1-9, workbook)

  18. Significant Digits in Math: • Use PS#1-10 to check your understanding of identifying significant digits in measurements. • See PS#1-11 for the rules about using significant digits in addition and subtraction. • See PS#1-11 for the rules about using significant digits in multiplication and division. Then go on and do PS#1-12.

  19. Accuracy & Precision Accuracy means that a measurement is close to the accepted value. Precision means that consistent results are obtained. A measurement can be precisely inaccurate. Demos: Balances Kilogram bathroom scale. Decigram balance. Centigram balance. Analytical balance.

  20. Significant Digits Significant Digits are those that can be accurately measured. The Rule for Sig. Digs. is to round off to the least accurate number of Sig. Digs. in the measurement.A chain is only as strong as its weakest link. Sample Problems: How many significant digits are in each of the following? a. 903.2 b. 0.009 0 c. 0.007 d. 0.02 e. 90.3 f. 0.090 0 g. 0.008 0 h. 70 i. 900.0 j. 99 k. 0.049 l. 5.000 2

  21. Scientific Notation Scientific Notation means to change your answers into "Standard Form" which is whole number then decimal. e.g. 5.29 X 108. Sample Problems: Change to scientific notation: a. 204 b. 12.89 c. 0.007 d. 0.00569 e. 46359.23 f. 23.5 X 105 g. 0.002 X 10-3 h. 423.2 X 10-14 i. 313 X 108 j. 5689 X 10-22

  22. Scientific Notation:Addition and Subtraction • Round to least precise measurement • Ex. 24.686 m 2.343 m + 3.21_m_ 30.239 m The correct answer is 30.24 m

  23. Scientific Notation:Multiplication and Division • Round to least amount of significant figures 3.22 cm X 2.1 cm 6.762 cm The answer would then be 6.8cm

  24. More Measurement: Orders of Magnitude-- Powers of Ten Direct Proportion-- up gives up. Inverse Proportion-- up gives down. Interpolation--finding points between points. Extrapolation-- finding points beyond the last point. Scalar-- gives magnitude only. 50 km/hr. Vector--gives magnitude & direction. 50 kph Northeast. It is represented by an arrow.

  25. Orders of Magnitude Video: Powers of Ten

  26. Linear Relationship Mass vs. Volume As the volume increases, so does the mass.

  27. Inverse Relationship As the speed increases, the time for the trip decreases.

  28. Terms: Matter-- has mass and occupies space. Mass -- quantity of matter measured by inertia. Inertia-- resistance to change in motion. Density = mass/volume. i.e. H20 1g/cc, Fe 8g/cc, Pb 11g/cc, Hg 14g/cc, Au 19g/cc Energy-- ability to do work. Potential Energy is stored energy, fuel, wound spring Kinetic energy is in motion, car zipping along. Law of Conservation of Matter & Energy-- Matter & energy cannot be created nor destroyed but only changed in form. E = mc2

  29. Density Problems D = DensityM = MassV = Volume D = M/V Find the density of a sample whose mass is 25.0 g and whosevolume is 82.3 cm3. Find the mass of a sample whose density is 8.2 g/ cm3 andwhose volume is 52.0 cm3. Find the volume of a sample whose mass is 250 g and whosedensity is 6.3 g/cm3.

  30. We Must Practice Physics

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