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Units of Measurement

posted Jan 30, 2015, 12:02 AM by Ranmini Perera   [ updated Sep 12, 2017, 9:48 PM by Upali Salpadoru ]





What do we measure?

Do you know that all our measure ments are based on 7 basic measurements?

What are they?






Symbols used here

The 'fundamental' units (Basic units) are named in red.
Others are 'Derived units'.

Measurement

Symbol

Units


Vector / Scalar.

Area.

A

m2

Square meters.

Scalar

Acceleration.

a

ms-2

Meters per second per second.

Centre of gravity

Centre of mass.

G

An imaginary point through which the weight of a body may be considered to act.

 Luminosity Cd. candela  Scalar

Current.

I or i.

A = Amperes.

Scalar

Density.

r  or d.

g.cm-3

Scalar

Displacement.

d.

M =Meter.

Vectar

Energy.

E

J=Joule.

Scalar

Force.

F or f.

N = Newton.

Vector.

Force gravitational.

g.



Vector.

Height.

h.

m.


Scalor.

Mass.

m.

kg= Kilogram.

Scalar

 Mole mol A  = 6.02 x1023 Scalar

Power.

P

W = Watt.

Scalar

Pressure.

Pr.

Pa.= Pacal.  Pa = Nm-2

Scalar

Period. (Time)

t.

s= second.

Scalar

Speed.

ms-1



Scalar

Temperature .

T.

K

Kelvin

Scalar

Velocity.

V

ms-1


Vectar.

Work.

Wk.

J= Joule.


Scalar.


                      A few common formulas using symbols.

  This is not according to the alphabetical order.

Word formula

Analysis

In symbols..

Area = L x L

Area  = m x m.

A= m2

Volume = L xL xL

Volume = mxmxm.

V = m3

Density.=mass/ volume.

Density = m/v.

d= .kg.m-3

Velocity

Velocity= meters/ seconds

V = ms-1.

Acceleration.

Acc.= Vfinal -Vinitial / time

     = Change in Velocity/ time.

a= ms-2

Energy (Gr. potential)

Eg= mass x gravity x height.

J = mgh.

Energy (Work)

Ew = Force x distance.

J= Nm.

Energy (Electrical)

Ee = Volt x current x time.

J = Vit.

J =i2rt.

Energy (Heat)

Heat =Mass x specific heat x time.

H = mct.

Energy (Kinetic)

Ek = ½ mass x velocity 2

Ek = 1/2kg.v2.

Power

Energy changed / time.

P = J/t .

 Force mass x acceleration F= ma.


A few more practical units.

Name

symbol

Definition

Frequency

Hz

Number of occurrence in one second.

Kilo watt hour.

kWH.

Quantity of electrical energy consumed in one hour.

Horse power.

Hp.

750 W.  ( Average power of a horse)

Micro farad.

μF

Electrical charge in a capacitor.

Decibel.

dB

Intensity of a sound.

Richter .

 

Log. Unit for Earth quakes.

For Richter scale, Mohr's hardness and wind scale click: Physical tables.



Prefixes used to change the size of units.


Some problems in using formulas.

1.0      The volume of a solid block  is  20 m3 .  The density is 6 kg m3. What is the weight of the mass?             

2.0      John getting a standing start runs 100m. in  15 s. gradually increasing velocity . Find the final velocity?

3.0      Jane has a mass of 50 kg and her cycle  20 kg. On riding at a speed of  10ms-1 a snake decides to cross her path. She brings the bike to a stop in 2 seconds. What was her braking power.

4.0      1.0 kW. Steel kettle of 250g. is used to heat 2 litres of water at 20C . Find the minimum time it will take to boil the water.

 5.0.      A car and passengers having a mass of 1500 kg. speeds up from 15m-s     30 m-s   in 3 seconds. Find the force car has used.

       For solutions  click- Answer page                                                                                     =  






 

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