1.4 ESTIMATION & ORDER OF MAGNITUDES

Estimation
· All measurement are estimations only
· Measurement is comparative value between object that to be measured and a standard scale or the theoretical value.
· Should be determined by accurate measurement

Order of magnitude

We frequently use prefixes to obtain units of more convenient size. Here are examples of commonly encountered prefixes :

1 nanometer = 1 nm = 10-9 m (a little bigger than an atom diameter)
1 micrometer = 1 μm = 10-6 m ( a human blood cell is about 7μm)
1 milimeter = 1mm = 10-3 m ( a pencil lead is about 0.5 mm in
diameter)
1 centimeter = 1 cm = 10-2 m (the diameter of a ballpoint pen)
1 kilometer = 1 km = 10 3 m (about 0.6 m)

1 microgram = 1 μg = 10-6 g = 10-9 kg (mass of a small dust particle)
1 miligram = 1 mg = 10-3 g = 10-6 kg (a raindrop is about 2 mg)
1 gram = 1 g = 10-3 kg = 10-3 kg (the mass penny is about 2.5g)

1 nanosecond = 1 ns = 10-9 s (time for light to travel 30 cm)
1 microsecond = 1 μs = 10-6 s (time for a rifle bullet to travel about 1mm)
1 millisecond = 1 ms = 10-3 s (about 14 ms between human heart beats)