Physics | Units and Measurements part 6 | for competitive exams

Pressure:

→ $\mathrm{Pressure}=\frac{\mathrm{Force}}{\mathrm{Area}}$

→ The force acting on a unit area of a surface is called pressure.

→ The pressure unit in the FPS system is pound-force per square inch (psi).

→ S.I unit of pressure is pascal or N/m² or N m^-2.

→ Bar is a unit of pressure.

→ The dimensional formula of pressure is M¹ L^-1 T^-2.

→ 1 bar = 10⁵ Pa

→ 1 bar = 10⁵ N/m²

→ 1 Pa = 1 N/m²

→ 1 atm = 101,325 Pa

→ Normal air pressure at sea level = 1013.25 millibars.

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Stress:

→ $\mathrm{Stress}=\frac{\mathrm{restoring\; force}}{\mathrm{area}}$

→ The S.I unit of stress is pascal.

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Strain:

→ Strain has no units and no dimensions.

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Surface tension:

→ $\mathrm{Surface\; tension}=\frac{\mathrm{Force}}{\mathrm{Length}}$

→ S.I unit of surface tension is N/m.

→ The dimensional formula of surface tension is M T^-2.

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Torque:

→ The turning or twisting moment of a force about an axis is called torque.

→ The S.I unit of torque is N m.

→ The dimensional formula of torque is M L² T^-2.

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Impulse:

→ Impulse can be defined as the force acting on a body for a short time.

→ Impulse = Force × time

→ The S.I unit of impulse is newton-second (Ns).

→ The dimensional formula of impulse is M L T^-1.

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Some important points:

→ The dobson unit is the most common unit for measuring ozone concentration in the atmosphere.

→ Distance and displacement have the same SI unit (unit → m).

→ Velocity and speed have the same SI unit (unit → m/s).

→ Force and weight have the same SI unit (unit → newton).

→ Work, energy and heat have the same SI unit (unit → joule).

→ Acceleration and acceleration due to gravity (g) have the same SI unit (unit → m/s²).

→ Momentum and impulse have the same SI unit (unit → kg m/s).

→ Pressure and stress have the same SI unit (unit → pascal).

→ Work, energy and torque have the same dimensional formula(M¹ L² T^-2).

→ Pressure and stress have the same dimensional formula(M¹ L^-1 T^-2).

→ Impulse and linear momentum have the same dimensional formula(M L T^-1).

→ Weight and force have the same dimensional formula(M L T^-2).

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Derived Units:

S. No.	Physical Quantity	SI Unit	Symbol
1.	Area	meter2	m2
2.	Volume	meter3	m3
3.	Density	kilogram/meter3	kg/m3 (or) kg m-3
4.	Momentum	kilogram meter/second	kg m/s (or) kg ms-1
5.	Velocity, Speed	meter/second	m/s (or) ms-1
6.	Acceleration	meter/second2	m/s2 (or) ms-2
7.	Angular velocity	radian/second	rad/s (or) rad s-1
8.	Angular acceleration	radian/second2	rad/s2 (or) rad s-2
9.	Force, weight	newton	N
10.	Work, Energy, Heat	joule	J
11.	Power, Radiant flux	watt	W
12.	Pressure, stress	pascal	Pa
13.	Frequency	hertz	Hz
14.	Resistance, Impedance, Reactance	ohm	Ω
15.	Resistivity or Specific resistance (ρ)	ohm-meter	Ω·m
16.	Electric charge	coulomb	C
17.	Electric Potential Difference (voltage), Electromotive force (emf)	volt	V
18.	Inductance	henry	H
19.	Capacitance	farad	F
20.	Magnetic flux	weber	Wb
21.	Magnetic flux density	tesla	T
22.	Luminous flux	lumen	lm
23.	Electrical conductance	siemens	S
24.	Radioactivity	becquerel	Bq

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