Energy and Technology definitions

Year 1 Sem 1&2

pressure in a liquid

P = pgh

cohesion and adhesion

the attractive forces within a liquid are known as cohesive forces, the forces between a liquid and a different substance are known as adhesion.

Surface Tension

The tension of the surface film of a liquid caused by the attractive of the particles in the surface layer by the bulk of the liquid, which tends to minimise surface area.

supercooled liquids

A supercooled liquid is an unstable liquid state below the normal freezing point.

Continuity of Flows

when fluids move through a full pipe, the volume of fluid that eneters the pipe must equal the volume of that leaves the pipe, even if the diameter of the pipe changes. Therefore: A₁v₁=A₂V₂

liquids and gases

gases can be compressed, liquids cannot

Vapours and Gases

Andrews showed that a gas has a critical temperature, above which it cannot be liquified by pressure.

Below critical temperature it is a vapour and can be liquified by pressure alone.

Dalton’s Law

states that the total pressure of a mixture of non-reacting gases is equal to the sum of the partial pressures of the individual gases.

Boyles’ Law

States that at a constant temperature, the volume of a fixed mass of gas is inversely proportional to its pressure.

Charles’s law

A gas expands or contracts by 1/273 of its original volume for every degree in fall/rise of temperature.

Work done (W) by a gas

W = P(delta)V

Catalyst

although a chemical reaction such as that between hydrogen and oxygen, releases energy, it requires activation energy to initiate the reaction (the match). A catalyst is a substance that can facilitate the reaction without the activation energy, emerging itself unchanged.

Five regions of the earth’s atmosphere

• Troposphere

• stratosphere

• mesosphere

• thermosphere

• exosphere

Ozone Layer

The ozone layer is in the stratosphere, where the molecules of O3 absorb most incoming UV radiation.

Runaway Greenhouse Effect

Refers to the increase in the natural greenhouse effect that is cause by human activities. Runaway is used because a warmer earth releases more greenhouse gases in a positive feedback loop, .e.g. methane from thawed permafrost.

standing wave speed

The speed of a wave in a vibrating string is given by:

v= (square root)T/mew

t=tension of the string

mew=the mass per unit length

the three mechanisims of heat transfer

• Conduction

• Convection

• radiation

Energy

the quantity that when transferred to a body does work on it, or heats up; it is measured in joules

Power

the rate at which energy or work is done and is measure in watts

Power and force

Power in watts = force and velocity.

Power and torque

Power in watts equal torque in N.m tine angular velocity

Friction Coefficient

Coefficient of friction equals force needed to move object divided by the normal force.

mew=coefficient

F=force needed to move object

R=the normal force