This document discusses the International System of Units (SI) used to measure physical quantities. It defines fundamental units like length, time and temperature, and derived units obtained by combining fundamental units, like volume. Multiples and submultiples are used to modify units. Dimensional analysis determines if equations are dimensionally correct by examining the dimensions of each term. Various instruments are described for measuring length, time, mass and weight at different scales, including vernier calipers, micrometer screws, stopwatches, balances and more. The key difference between mass and weight is also noted.

1. Physics
Units and measurements
SHORT REVISION SERIES

2. SI UNITS
 International system of units.
Acceptable system of units globally.
 Fundamental quantities: Time,
temperature, lenght etc
 Derived quantities: Combination of
fundamental units and quatities:
volume =lxbxh => m x m x m = m3
 Density = mass/volume =>kg/m3

3. Multiples and submultiples
multiples
10 Deca
(da)
102 Hecto
(h)
103 Kilo (k)
104 Mega
(M)
105 Giga
(G)
106 Tera (T)
submultip
les
10-1 Deci
10-2 Centi
10-3 Milli
10-4 Micro
10-5 Nano
10-6 Pico

4. DIMENSION OF PHYSICAL
QUANTITY
 We employ the concept of
dimension to express the make up
of a physical quantity.
 Dimension is expressed in terms of
lenght L, mass M, time T.
Pressure = Force/Area =N/m2 = m
a/m2
 Now the dimension of ma = mass (M)
x acceleration (v/t)
 Velocity= displacement/time= s/t

5. acceleration=s/t/t = s/t2
Substitute the terms of
dimension acceleration
=L/T2 or LT-2
Pressure = force/area =
mass x acceleration/ area =
MLT-2/L2 =
•ML-1T -2

6. To determine if an equation is
dimensionally correct
 s = ut + ½ at2
o s = distance, u = initial vel, a = acceleration
 Dimension of s = L
 Dimension of ut = s/t x t = L/T x T = L
 Dimension of ½ at2 = s/t2 x t2 = L/T2 x T2 = L
 As you can see all the dimension of each term
are the same

7. Measurements of lenght
 Longer lenght: Graduated tapes
 Shorter lenght: metre rule
 Smaller lenght such as internal diametre of
test tube, diametre of a rod: use vernier
calipers
 Micro small lenght where greater accuracy is
required such as diametre of a wire or
thickness of paper use micrometre screw
guage

8.  Vernier’s calipers:
Accuracy: 0.01cm or 0.1 mm
Has 2 scales: The main scale M
graduated in mm
The Vernier scale V used to divide the
main scale to smaller callibrations
Micrometre screw guage:
Has a main scale graduated in mm and a
circular vernier scale that contains 50
divisions.

9. Measurement of time
 Solar day
 Stop watch

10. Measurement of mass and
weight
 Mass : Beam balance
 Weight: Lever balance, dial balance,
spring balance
Note the difference between mass
and weight
 Mass is the quantity of matter in a
body while weight is earth’s pull on
a body

11. END