5. Work, Energy and Power

Energy stores

Gravitational → stored due to height from ground

Elastic → stored in elastically deformed objects [squeezed/stretched]

Chemical → stored due to chemical configuration [food, fuels, batteries]

Kinetic → stored in moving objects

Magnetic → stored in magnets

Electrostatic → stored in charges

Nuclear → stored in nucleus of an atom

Thermal → stored (and lost) in surroundings

GECKMENT

Energy transfers

Heating → from horror to cooler objects (usually lost to surroundings through convection, conduction..)

Electrically → energy transfer through flow of current

Radiation → energy transfer due to sound and light waves

Mechanically → through forces acting on a system

HERM

Walk through stores and transfers in a circuit w/ bulb

1. There is a chemical store in the battery

2. The chemical store from battery is transferred electrically into a thermal store in the bulb

3. The thermal store in the bulb is transferred/dissipated to surroundings through light radiation and heating

Principle of conservation of energy

Energy can neither be created nor destroyed, it can only be transferred from one energy store to another store by different pathways

Define : energy

The amount of work a physical system is capable of performing

Define : work

A measure of the change a force produces

Work done formula

Work done (joules) = force (Newtons) x distance (meters)

Define : Power

the rate of doing work (amount of work done in a specific period if time)

Equation for power

Power (watts) = Energy Transferred (J) or work done (J) / Time Taken (sec)

define : gravitational potential energy (GPE)

Energy stored in an object due to its position or height within a gravitational field

Equation for GPE

GPE (joules) = mass (kg) x gravitational field strength (10N/Kg) x height (m)

Diving board and GPE example

GPE = 80kg x 10N/kg x 10m = 8000 Joules

It took 8000 joules of work (W=FxD) to get up, and 8000 Joules of chemical energy eaten to sustain him to get up

How to calculate force (applied by human) in W= f x d

Force = weight

Weight = mass x gravitational field strength

If baguette is dropped from top of Eiffel Tower with 1620Joules of gravitational potential energy, what happens to Kinetic energy and GPE

As its dropped, GPE gets smaller as height drops

The energy is transferred into kinetic energy

Just before it hits the ground, it should have 1620Joules of Kinetic energy

Define : Kinetic Energy

The amount of energy an object has in its kinetic stores as a result of its mass and speed

Equation for kinetic energy

KE (joules) = ½ x mass (kg) x speed² (m/s)

KE = ½ x m x v²

Efficiency equation

%efficiency = [(useful energy output) / (total energy input)] x 100

1 Watt is..

1 joule of energy transferred/work done in 1 sec

What is a Sankey Diagram

Diagrammatic representation of how energy is transferred

The width of arrows = amount of energy transferred