1. Chapter 1 Physical Quantities and Units Part 2 – Length & Time In the quest to understand nature, scientists use physical quantities to describe the world around us.

7. engineer’s calipers A pair of engineer’s calipers and ruler are used for measuring the lengths of objects without any flat sides. measurement of length the jaws are closed until the points just touch the object to be measured remove the calipers and measure the distance between the jaws with a ruler.

8. Vernier calipers measure small lengths accurately up to 0.01 cm. vernier calipers measurement of length accuracy = 0.1 mm / 0.01 cm inside jaws outside jaws main scale vernier scale tail

9. reading on main scale (between A and B) = 2.4 cm reading on vernier scale (C) = 0.08 cm actual reading of object = 2.4 + 0.08 = 2.48 cm vernier calipers measurement of length main scale (fixed) vernier scale (movable) object being measured A B C 9 mm

10. vernier calipers measurement of length When the two jaws of the vernier calipers touch each other, both zero marks on the main scale and on the vernier scale should coincide. If not, there is a zero error in the vernier calipers.

11. supposing observed reading is 3.24 cm, then corrected reading = observed reading – zero error = 3.24 – (+0.01) = 3.23 cm measurement of length 0 10 5 zero error = +0.01 cm main scale (fixed) vernier scale (movable) 0 1 If the two jaws touch each other, but the zero marks of the main scale and vernier scale do not coincide as shown below, the zero error is positive . vernier calipers

12. supposing observed reading is 4.03 cm, then corrected reading = observed reading – zero error = 4.03 – (-0.02) = 4.05 cm measurement of length 0 10 zero error = -0.02 cm main scale (fixed) vernier scale (movable) 0 1 If the two jaws touch each other, but the zero marks of the main scale and vernier scale do not coincide as shown below, the zero error is negative . 5 vernier calipers

13. micrometer screw gauge measurement of length accuracy = 0.01 mm / 0.001 cm anvil spindle sleeve thimble ratchet frame Micrometers measure small diameters or thicknesses.

14. micrometer screw gauge measurement of length reading on sleeve = 4.5 mm reading on thimble = 0.12 mm actual reading of object = 4.5 + 0.12 = 4.62 mm thimble sleeve

15. measurement of length micrometer screw gauge When the anvil and spindle of the micrometer touch each other, the scales should read zero. If not, there is a zero error in the micrometer.

16. measurement of length micrometer screw gauge If the anvil and spindle touch each other, but the scales do not read zero as shown below, the zero error is positive . supposing observed reading is 2.37 mm, then corrected reading = observed reading – zero error = 2.37 – (+0.02) = 2.35 mm } 2 divisions

17. measurement of length micrometer screw gauge If the anvil and spindle touch each other, but the scales do not read zero as shown below, the zero error is negative . supposing observed reading is 2.87 mm, then corrected reading = observed reading – zero error = 2.87 – (-0.03) = 2.90 mm } 3 divisions

24. ticker-tape timer measurement of time An electrical device that makes use of the oscillations of a steel strip to mark short intervals of time. steel strip magnet coil ticker-tape drawing pin carbon paper disc 6 ~ 12 V a.c.

26. e.g. metre rule half-metre rule measuring tape vernier calipers micrometer screw gauge pendulum clock watch stopwatch ticker-tape timer length (m) mass (kg) time(s) electric current (A) temperature (K) amount of substance (mol) luminous intensity (cd) Prefixes Measurement Physical quantities are made up of can be measured with e.g. of Numerical values and suitable units Vector Scalar Base quantities Base SI units Time Length micro (  ) 10 -6 milli (m) 10 -3 centi (c) 10 -2 deci (d) 10 -1 kilo (k) 10 3 mega (M) 10 6 may be include use such as for can be measured with