PHY101 Short Notes

PHY101 Short Notes

Physics ↔ study of nature (figure 1.2) Matter is studied at all levels: macroscopic → microscopic e.g. gold cube → atoms → nuclei → quarks Also, the different forces that are predominant at these different levels: gravitational → electric → strong → weak

Tools for our investigations: Units

Standard units SI (System International)  Length m (meter)  Mass kg (kilogram)  Time s (second) Also, Gaussian CGS  cm (centimeter)  g (gram)  s (second) And British Engineering (or US Customary units) BE  ft (feet)  sl (slugs)  s (seconds) → need conversion of units: 1 inch ≈ 2.54 cm 1 foot ≈ 0.3 m etc. 1 pound = 4.45 N (Force!)

Other units are derived from these: eg. 1 Newton = 1 kg * m …. s 2 & Prefixes: kilo (k) → 103 mega (M) → 106 giga (G) → 109 tera (T) → 1012 milli (m) → 10-3 micro (μ) → 10-6 nano (n) → 10-9 pico (p) → 10-12

Lengths

distance to the farthest quasar 1026 m a galaxy the nearest star ~1021 m 4 x 1016 m Pluto 6 x 1012 m

diameter of the Sun ~109 m radius of the Earth ~ 6 x 106 m Mt. Everest 9 x 103 m Statue of Liberty 102 m man ~ 1 m computer chip 10-3 m red blood cell 10-5 m length of virus 10-8 m radius of atom 10-10 m radius of nucleus 10-15 m

Time

Age of universe ~5 x 1017 s Age of pyramids ~1011 s Human life expectancy (US) ~2 x 109 s A day 9 x 104 s Time between heartbeats 8 x 10-1 s Flapping of housefly wings ~10-3 s Lifetime of μ 2 x 10-6 s Time required for a microprocessor to execute an instruction ~2 x 10-9 s Fastest transistors (operation time) ~10-12 s Lifetime of most unstable particles ~10-23 s

Uncertainty (accuracy) in measurement – related to the sensitivity of the apparatus eg. using a meter stick → 1 mm vs. a caliper → 0.1 mm vs. a micrometer → 0.01 mm

Significant Figures

A significant figure is a reliably known digit. eg. measure the area of a rectangular plate using a meterstick. Accuracy: ± 1 mm or ± 0.1 cm Measure: L = (16.3 ± 0.1) cm i.e. 16.2 ↔ 16.4 cm Similarity: W = 4.5 cm (± 0.1 cm) i.e. 4.4 ↔ 4.6 cm → in our case: 16.3 has 3 sig. figs.

4. 5 has 2 sig. figs.

If we now calculate the area: A = L x W = (16.3 cm) (4.5 cm) = 73.35 cm2 the answer, though, is = 73 cm2 (2 sig. figs.)