What is Physics?

1. What is Physics?

2. What is Physics?

3. Feb 28, 2009Merlion hit by lightning A lightning bolt struck the Merlion statue at about 4.30pm yesterday. The national icon at One Fullerton facing the Singapore River lost part of its top left mane and is believed to have its right ear chipped. About 20 to 30 people nearby, including tourists, ran helter-skelter in the pouring rain when debris from the Merlion's head went flying. Some ran to safety in the nearby shops and cafes. The fragments fell onto the patio at One Fullerton and the Singapore River Cruise counter near the Merlion. Nobody was hurt. Eyewitness Ms RinaToh, 17, a barista at The Coffee Bean and Tea Leaf at One Fullerton, said: 'I saw a bright Z-shaped lightning bolt, and it was a lot bigger than usual.' She was standing at the counter and could see the Merlion.

4. What is Physics? • Physics is the study of the natural world around us – from the very large, such as the solar system, to the very small, such as the atom.

5. In the quest to understand nature, scientists use physical quantities to describe the world around us. Physical Quantities, SI Units and Measurement Chapter 1

6. At the end of this chapter… You should be able to: • show understanding that all physical quantities consist of a numerical magnitude and a unit • recall the following base quantities and their units: mass (kg), length (m), time (s), current (A), temperature (K) • use the following prefixes and their symbols to indicate decimal sub-multiples and multiples of the SI units: nano (n), micro (μ), milli (m), centi (c), deci (d), kilo (k), mega (M)

7. At the end of this chapter… You should be able to: • show an understanding of the orders of magnitude of the sizes of common objects ranging from a typical atom to the Earth • describe how to measure a variety of lengths with appropriate accuracy by means of tapes, rules, micrometers and calipers, using a vernier scale as necessary • describe how to measure a short interval of time including the period of a simple pendulum with appropriate accuracy using stopwatches or appropriate instruments

8. Cubit

9. Why do We Need to Measure Things? • Let’s do this as a class… • Work in groups of two • Compare the length between the elbow to the first finger tip.

10. Why do We Need to Measure Things? • Are they the same?

11. Physical Quantities and SI Units Base Quantity Symbol for SI Unit Name of SI unit Length metre m Mass kilogram kg Time second s Electric Current ampere A Temperature kelvin K Intensity candela cd Amount of Substance mole mol

12. actual length = 0.850 m Physical Quantities • A physical quantity when measured may be described in terms of • A number • Its unit of measurement

13. Physical Quantities • What is your height? • 2 m quantity unit

14. Physical Quantities • Mass – unit of measurement, kilogram (kg)

15. Physical Quantities • Time – unit of measurement, second (s)

16. Physical Quantities • What are some problems we might face in our daily lives if there are no standard measurements?

17. 1.4 Gm (gigametre) 0.2 mm (millimetre) Do You Know??? Diameter of the Sun Thickness of a strand of hair 1 400 000 000 m 0.0002 m

18. Prefixes for SI units Factor Prefix Symbol 9 10 giga- G 6 10 mega- M 3 10 kilo- k - 1 10 deci- d - 2 10 centi- c - 3 10 milli- m - 6 10 micro- µ - 9 10 nano- n

19. Prefixes Exercise 1 Express the following quantities in their respective SI unit. • One kilometer = 1000m or 103m • One microsecond = 0.000001s or 10-6s • One centimeter = 0.01m or 10-2m • One gram = 0.001kg or 10-3kg

20. Prefixes Exercise 1 • One miligram = 0.001g or 10-3g =10-6 kg • One millisecond = 0.001s or 10-3s • One minute = 60s • One hour = 3600s

21. What does SI units mean? • Système International • International System of Units

22. Measurement of Length • The SI unit for length is ( ) • Other units for length: m metre millimetre (mm), centimetre (cm), kilometre (km)

23. Measuring Tape Metre/Half- metre Rule Measurement of Length 0.1 cm (or 1 mm) 0.1 cm (or 1 mm) Vernier Calipers 0.01 cm (or 0.1 mm) Micrometer Screw Gauge 0.001 cm (or 0.01 mm)

24. Measurement of Length Measuring Tape - Length of classroom, car, corridor • Metre rule: • Length of desk, book

25. cm 1 2 3 Measurement of Length • Parallax Error What is Parallax Error? It is the error which arises due to incorrect positioning of the eye. 2.7 cm correct 3.0 cm wrong

26. 2.7 cm correct 3.0 cm wrong cm 1 2 3 Measurement of Length • Parallax Error How do we avoid Parallax Error? • Always place the eye vertically above the mark being read. OR • Place the eye in level with the mark being read.

27. Vernier Calipers • French scientist Pierre Vernier(1580-1637) Accuracy: 0.01 cm (or 0.1 mm)

28. Measured Value How to read off the Vernier Caliper? 11mm 0.7mm mm Reading = 11 mm + 0.7 mm = 11.7 mm

29. Vernier CalipersIts structure and its application • The inside jaws is used to measure internal diameter of test-tube, ring etc. In main scale, reading = 1.90 cm in vernier scale, reading = 0.01 cm the actual reading = 1.91 cm

30. Vernier CalipersIts structure and its application • The outside jaws is used to measure small length, diameter of test-tube etc. main scale reading = 4.20 cm vernier scale reading = 0.06 cm Actual reading = 4.26 cm

31. Exercise 1 mm Reading = 19 mm + 0.4 mm = 19.4 mm

32. Exercise 2 mm Reading = 4 mm + 0.7 mm = 4.7 mm

33. Exercise 3

34. Exercise 4

35. Exercise 5 mm Reading = 12 mm + 0.6 mm = 12.6 mm

36. Exercise 6 mm Reading = 7 mm + 0.5 mm = 7.5 mm

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38. 0 10 main scale (fixed) 0.1mm vernier scale (movable) 5 0 10 Vernier Calipers • Zero Error (Vernier Calipers) • Positive Zero Error +0.1 mm • Zero Error = mm • If the observed reading = 32.4mm, then • Actual measurement = Observed reading – Zero error • = mm • = cm +0.1 32.4 - (+0.1) 32.3

39. Vernier Calipers • Zero Error (Vernier Calipers) • Negative Zero Error 0 10 main scale (fixed) 0.1mm vernier scale (movable) 5 0 10 - 0.2 mm • Zero Error = mm • If the observed reading = 32.4 mm, then • Actual measurement = Observed reading – Zero error • = mm • = mm - 0.2 32.4 - (-0.2) 32.6

40. Micrometer Screw Gauge • Accuracy: 0.001 cm (or 0.01 mm) • Smaller length, such as diameter of thin wire, thickness of a piece of paper etc can be measured by micrometer screw gauge.

41. Micrometer Screw Gauge 3 mm 0.09 mm Sleeve reading = mm Thimble reading= mm Reading = mm Reading = cm 3.0 0.09 3.09 0.309

42. Micrometer Screw Gauge 0.30 mm 5.5 mm Sleeve reading = mm Thimble reading= mm Reading = mm Reading = cm 5.5 0.30 5.80 0.580

43. Micrometer Screw Gauge 0.06 mm 3.5 mm Sleeve reading = mm Thimble reading= mm Reading = mm Reading = cm 3.5 0.06 3.56 0.356

44. Exercise 1 11.5mm 0.25mm Reading = 11.5 mm + 0.25 mm = 11.75 mm

45. 30 15 20 25 20 15 Exercise 2 Reading = 20.5 mm + 0.22 mm = 20.72 mm

46. Micrometer Screw Gauge • Zero Error (Micrometer Screw Gauge) • Positive Zero Error +0.02 mm • Zero Error = mm • If the observed reading = 2.37mm, then • Actual measurement = Observed reading – Zero error • = mm • = mm +0.02 2.37 - (+0.02) 2.35

47. Micrometer Screw Gauge • Zero Error (Micrometer Screw Gauge) • Negative Zero Error - 0.03 mm • Zero Error = mm • If the observed reading = 2.37mm, then • Actual measurement = Observed reading – Zero error • = mm • = mm - 0.03 2.37 - (- 0.03) 2.40

48. Measurement of Time • Stopwatches are used to measure short intervals of time. • Two types: • Digital stopwatch • Analogue stopwatch • SI unit of time: second, s

49. Measurement of Time 1 s 0.1 s 0.01 s

50. Measurement of Time • Watch/Clock • used for measuring long intervals of time • most modern watches depend on the vibration of quartz crystals to keep time accurately • the energy that keeps these crystals vibrating comes from a small battery • many watches still make use of coiled springs to supply the needed energy