1.1
The Realm of Physics
The order of magnitude is the nearest power of 10 after first writing in standard form and then
rounding off to the nearest 1, 10, 100, 1000, etc. 230 is second order of magnitude. 790 is third
order. 8000 is 4th order.
Sizes from 10
15
m to 10
+25
m (subnuclear particles to extent of the visible universe).
Masses from 10
30
kg to 10
+50
kg (electron to mass of the universe).
Times from 10
23
s to 10
+18
s (passage of light across a nucleus to the age of the universe ).
The difference in orders of magnitude between two values with the same units is found by dividing
the two values.
1.2
Measurement and Uncertainties
The fundamental units are kilogram, meter, second, ampere, mole and kelvin.
Derived units are formed by multiplying and dividing fundamental units. The speed unit is derived
from dividing metres by seconds.
Units can be converted from one to another by multiplying or dividing by the appropriate factor. An
hours is equal to 3600 seconds. To convert metres per second to kilometers per hour, multiply by
3.6.
The accepted way of writing derived units is to use negative indices where required e.g. m s
1
for
speed.
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 Spring '11
 JamesInstor
 Physics, Power, 25 m, 15 m, 50 kg, 30 kg, 2.3 kiloJoules

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