pressure and unit

What is pressure

Force acting per unit area.

SI unit of pressure

Pascal (N/m²).

Formula of pressure

P = F/A.

Why does a sharp nail penetrate easily

Small area → more pressure.

Why do trucks have broad tyres

Large area → less pressure.

Pressure in liquids depends on

Depth, density, gravity (P = hρg).

Pressure in gases depends on

Speed & collision of particles.

Equation of state of gases

PV = nRT.

Unit of atmospheric pressure

Bar.

Instrument to measure atmospheric pressure

Barometer.

Average atmospheric pressure at sea level

1013.25 hPa or 1 atm.

Atmospheric pressure decreases with

Increase in height.

Whose nose bleeds at high altitude

Mountaineers, due to low pressure.

Bernoulli’s principle is based on

Law of conservation of energy.

Pascal’s law statement

External pressure on fluid transmits equally in all directions.

Applications of Pascal’s law

Hydraulic brakes & lift.

What is buoyant force

Upward force exerted by fluid on immersed body.

Archimedes’ principle

Buoyant force = weight of displaced fluid.

Why does a ship float

Shape displaces more water → more buoyancy.

Why does a submarine sink

By filling water inside → density increases.

Why does hot air balloon rise

Hot air density < cold air.

Instrument to measure liquid density

Hydrometer.

Density of seawater vs river water

Sea water density higher → easier to float.

Heat is a form of

Energy due to molecular motion.

SI unit of heat

Joule.

1 calorie =

4.2 Joules.

Heat flows from

High temperature → low temperature.

Normal human body temperature

36.9°C or 98.4°F.

At what temp Celsius = Fahrenheit

-40°.

Thermometer for very high temp

Pyrometer.

Thermometer for very low temp

Cryometer.

Which liquid used in thermometers at very cold regions

Alcohol.

Freezing point of mercury

-39°C.

Freezing point of alcohol

-115°C.

Methods of heat transfer

Conduction, Convection, Radiation.

Conduction is most effective in

Solids (esp. metals).

Convection occurs in

Liquids & gases.

Radiation requires

No medium (occurs in vacuum).

Example of conduction

Spoon in hot tea becomes hot.

Example of convection

Sea breeze & land breeze.

Example of radiation

Heat from Sun reaches Earth.

Good conductors of heat

Copper, aluminium, iron.

Bad conductors of heat

Wood, plastic, glass, air.

Why sweaters keep warm

Air trapped acts as bad conductor.

Why 2 thin blankets warmer than 1 thick

Air trapped between them.

Why igloos keep warm

Ice is bad conductor, retains body heat.

Why black surface heats faster

Absorbs more heat.

Why tea cups are white & smooth

Reflects heat, keeps tea hot longer.

Effect of heat on matter

Expansion (solid, liquid, gas).

Exception in expansion

Water between 0°C–4°C.

At what temp water density max

4°C.

What is specific heat

Heat to raise 1g substance by 1°C.

Which liquid has highest specific heat

Water (due to H-bonding).

Why water used in car radiator

High specific heat → absorbs more heat.

What is latent heat

Heat absorbed/released during change of state.

Why steam burns severe than boiling water

Steam has latent heat.

Change of state liquid → gas

Evaporation.

Gas → liquid

Condensation.

Liquid → solid

Solidification.

Solid → gas

Sublimation.

Gas → solid

Deposition.

Who gave 3 laws of motion

Sir Isaac Newton.

Book where laws of motion published

Principia Mathematica (1687).

Newton’s 1st law

Law of inertia.

Newton’s 2nd law formula

F = ma.

Newton’s 3rd law

Every action has equal & opposite reaction.

SI unit of force

Newton (N).

Linear momentum formula

p = mv.

Acceleration due to gravity (g)

9.8 m/s².

Universal gravitational constant (G)

6.67 × 10⁻¹¹ Nm²/kg².

g is maximum at

Poles.

g is minimum at

Equator.

Value of g in Shimla vs Mumbai

Less in Shimla (hilly area).

Weight formula

W = mg.

Weight on Moon vs Earth

1/6th.

A person 60 kg on Earth weighs how much on Moon

10 kg.

Escape velocity on Earth

11.2 km/s.

Orbital velocity for Earth satellites

7.9 km/s (~8 km/s).

Geostationary satellite altitude

~36,000 km.

Centripetal force acts

Towards center.

Centrifugal force acts

Away from center (pseudo force).

SI unit of work

Joule.

SI unit of power

Watt (J/s).

1 Horsepower =

746 W.

Formula for kinetic energy

KE = ½ mv².

Formula for potential energy

PE = mgh.

Law of conservation of energy

Energy can neither be created nor destroyed.

Example of energy conversion: Electrical → Mechanical

Fan, motor.

Example: Electrical → Heat & light

Bulb, heater.

Example: Sound → Electrical

Microphone.

Example: Electrical → Sound

Speaker.

What is surface tension

Tension caused by cohesive force on liquid surface.

Effect of detergent on surface tension

Decreases, helps cleaning.

Effect of temperature on surface tension

Decreases with increase in temperature.

What is viscosity

Resistance to flow of liquid/gas.

High viscosity fluid example

Honey.

Low viscosity fluid example

Water.

Effect of temperature on viscosity of liquids

Decreases.

Effect of temperature on viscosity of gases

Increases.

Wave motion definition

Transfer of energy through medium without transfer of matter.