Types of Energy HeatChemical LightGravitational SoundElastic/strain KineticNuclear Electric

The Law of Conservation of Energy Energy can be changed (transformed) from one type to another, but it can never be made or destroyed.

Energy Flow diagrams We can write energy flow diagrams to show the energy changes that occur in a given situation. For example, when a car brakes, its kinetic energy is transformed into heat energy I the brakes. Kineticheat

Other examples When a rocket launches. Chemicalkinetic + sound + heatgravitational

Sankey Diagram A Sankey diagram helps to show how much light and heat energy is produced

Sankey Diagram The thickness of each arrow is drawn to scale to show the amount of energy

Efficiency Although the total energy out is the same, not all of it is useful.

Efficiency Efficiency is defined as Efficiency (%) = useful energy outputx 100 total energy input

Energy efficient light bulb Efficiency = 75 x 100 = 75% 100

Heat can travel by Convection A hot fluid expands, so is less dense, so rises. Cold fluid takes its place. A convection current can be formed.

Examples of Convection

Heat can travel by Conduction Hot particles vibrate more, so collide with adjacent particles. The heat energy travels from hot to cooler areas. hot cold

Heat can travel by Conduction Metals are good conductors of heat They have free electrons that can move from atom to atom carrying thermal energy too

Heat can travel by Conduction Gases are poor conductors of heat (insulators) The atoms are too far apart for the vibrations to be passed easily.

Infrared radiation Heat can travel by infrared radiation (“Hot light”!)

Infrared radiation Infrared radiation can travel through a vacuum (and through air)

Infrared radiation Black objects are good absorbers of infrared radiation.

Infrared radiation Shiny objects reflect infrared radiation. Nottingham Forest winning the champions league in 1979

Infrared radiation Black objects are good EMITTERS of IR radiation 100°C Shiny!

Vacuum Flask (“Thermos”)

The insulated lid stops the heat escaping (and entering) by convection

The vacuum between the two walls stops the heat escaping (and entering) by conduction vacuum

The silvered inner and outer stops the heat escaping (and entering) by radiation silvered outer silvered inner

This means hot liquids stay hot because the heat cannot escape Hot chocolate

This means cold liquids stay cold because the heat cannot enter Cold Vimto

Work In physics, work is the amount of energy transformed (changed) when a force moves (in the direction of the force)

Calculating work The amount of work done (measured in Joules) is equal to the force used (Newtons) multiplied by the distance the force has moved (metres). Force (N) Distance travelled (m)

Work done = Force x Distance Another sexy physics formula to learn!

Work done (J) = Force (N) x distance (m) A woman pushes a car with a force of 400 N for a distance of 15m. How much work has she done? Work = force x distance = 400 x 15 = 6000 J

Work done (J) = Force (N) x distance (m) A man lifts a mass of 120 kg to a height of 2.5m. How much work did he do? Force = weight = 1200N Work = F x d = 1200 x 2.5 Work = 3000 J

Power! Power is the amount of energy transformed (changed) per second. It is measured in Watts (1 Watt = 1 J/s) Power = Energy transformed time

Gravitational potential energy E p = mgh Can you copy this please? J kg N/kg or m/s 2 m

Example On earth g = 10 m/s 2 Height = 3.4 km = 3400 m Mass of dog = 12 kg GPE of dog = mgh = 12 x 10 x 3400 = J

Kinetic energy Kinetic energy of an object can be found using the following formula E k = mv 2 2 where m = mass (in kg) and v = speed (in m/s)

Example A bullet of mass 150 g is travelling at 400 m/s. How much kinetic energy does it have? E k = mv 2 /2 = (0.15 x (400) 2 )/2 = J

Energy changes

Example GPE of dog = mgh = 12 x 10 x 3400 = J Just before the dog hits the ground, what has this GPE turned into? Kinetic energy

Example GPE of dog = mgh = 12 x 10 x 3400 = J KE at bottom = J Just before the dog hits the ground, what has this GPE turned into? Kinetic energy

Example GPE of dog = mgh = 12 x 10 x 3400 = J KE at bottom = J = mv 2 /2 Just before the dog hits the ground, what has this GPE turned into? Kinetic energy

Example = mv 2 /2 Just before the dog hits the ground, what has this GPE turned into? Kinetic energy

Example = mv 2 /2 2 x = 12 x v 2 Just before the dog hits the ground, what has this GPE turned into? Kinetic energy

Example = mv 2 /2 2 x = 12 x v = 12v 2 Just before the dog hits the ground, what has this GPE turned into? Kinetic energy

Example = mv 2 /2 2 x = 12 x v = 12v = v 2 Just before the dog hits the ground, what has this GPE turned into? Kinetic energy

Example = mv 2 /2 2 x = 12 x v = 12v = v = v v = 261 m/s Just before the dog hits the ground, what has this GPE turned into? Kinetic energy

Non-renewable Finite (being depleted – will run out) In general a form of potential energy released by human action

Renewable Will not run out (in the near future) Mostly directly or indirectly linked with the sun (the exception is tidal energy)

Fossil fuels - Advantages Relatively cheap Can produce a lot of energy Variety of engines and devices use them directly and easily Extensive distribution network in place

Fossil fuels - Disadvantages Will run out Coal in particular produces acid rain Oil spillages etc. Contribute to the greenhouse effect by releasing greenhouse gases

Nuclear power - Advantages High power output Large reserves of nuclear fuels No greenhouse gases

Nuclear power - disadvantages Waste products dangerous and difficult to dispose of Major health hazard if there is an accident Produces material for Nuclear weapons

Solar power - advantages “Free” Renewable Clean

Solar power - disadvantages Only works during the day Affected by cloudy weather Low power output Requires large areas Initial costs are high

Hydroelectric - Advantages “Free” Renewable Clean

Hydroelectric - disadvantages Very dependent on location Drastic changes to environment (flooding) Initial costs very high

Wind power - advantages “Free” Renewable Clean Ideal for remote locations

Wind power - disadvantages Works only if there is wind! Low power output Unsightly (?) and noisy Best located far from cities High maintainance costs

Wave power - Advantages “Free” Reasonable power Renewable Clean

Wave power - disadvantages Only in areas with large waves Waves are irregular Maintainance and installation costs high Transporting power Must withstand storms/hurricanes