posted Jan 30, 2015, 12:02 AM by ranmini@charliesresearch.com [ 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
|
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Vector / Scalar.
|
|
Area.
|
A
|
m2
|
Square meters.
|
Scalar
|
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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
|
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Density.
|
r or d.
|
g.cm-3
|
Scalar
|
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Displacement.
|
d.
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M =Meter.
|
Vectar
|
|
Energy.
|
E
|
J=Joule.
|
Scalar
|
|
Force.
|
F or f.
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N = Newton.
|
Vector.
|
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Force gravitational.
|
g.
|
|
|
Vector.
|
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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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