CHAPTER 1: MECHANICS

1.1 Basic Quantities & SI Units

measured

value unit

1 m, 80 ms-1

Length, intensity, force, speed & etc.

derived

combining

l

m

t

I

T

meter

kilogram

second

Ampere

Kelvin

m

kg

s

A

K

Quantity of matter mol mole K

Relationship with base units

SymbolDerived

unit

m ÷ s

m x v

ms-1 ÷ s

kg x ms-2

N ÷ m2

kg x ms-2

v

p

a

F

P

W

ms-1

kgms-1

ms-2

N

Pa orNm-2

N

• Dimensions of physical quantities relates the physical quantities to the basic quantities such as mass (M), length (L), time (T), electric current (A), temperature (θ) and quantity of matter (N).

1.2 Dimensions of Physical Quantities

• Examples: • [velocity] = [length] / [time]

= LT-1

• [force] = [mass] [acceleration] = [mass] x [change of velocity] / [time]

= MLT-2

Uses of Dimensions

• To check the homogeneity of a physical equation

• To derive a physical equation

500 m

500 m

no

left

distance displacement

speed velocity

1.4 Errors

• Two types of errors:

(i) Systematic errors

(ii) Random errors

(i) Systematic errors

• Sources of systematic errors:• Instruments• The observers• The surroundings

• Definition: • uncertainties in the measurements of a

physical quantities due to instruments, physical conditions of surrounding & physical limitations of the observer. (roughly constant)

(ii) Random errors• Sources of systematic errors:

• Mistakes made by the observer when taking measurements

• The surroundings and the instruments used

• Can be reduced by:• Taking several readings and

calculating the mean.

Review Exercises 1