P1 - Energy

energy cannot be created or destroyed, only transferred from one from to another 

a system is an object or group of objects. when a system changes, energy is transferred either into or away from the system

energy can be transferred mechanically (by doing work), electrically, heating, or by radiation

internal energy is made up of:

• kinetic energy - energy due to the movement of the particles 
• potential energy - energy due to the particles' molecular attraction

efficiency is a measure of the amount of useful energy transferred

only some of the energy in a system is usefully transferred, with the rest wasted (dissipated or used for an unneeded purpose)

eff = useful out / total in

write as a percentage or decimal 

factors that effect GPE=

• height above the ground 
• gravitational field strength
• mass

GPE (J) = mass (kg) * gfs (N/kg) * height (m)

if the gravitational field strength is unknown, use the number 10 N/kg

this is the energy stored in any moving object

KE depends on=

• the mass of the object
• the speed that it is traveling at

KE (J) = mass (kg) * velocity² (m/s) * 0.5

GPE = KE (assuming all of the KE in the falling object has been converted into GPE)

this number is usually inaccurate because of friction and air resistance, the amount of GPE is usually lower than the original KE value.

hooke's law states that the amount of force acting on a spring is determined by its length and its spring constant

force (N) = extension (m) * spring constant (N/m)

on a graph, you can see the elastic limit at the point where the force needed to extend the string becomes extremely minimal

the higher the spring constant, the more force needed to extend it, and the harder it is to stretch

elastic energy is the amount of energy needed to stretch a spring basically

elastic energy (J) = 0.5 * spring constant (N/m) * extension² (m)

work is the transfer of energy

factors affecting work done:

• distance moved
• force applied 

work done (J) = force (N) * distance (m)

power is the rate at which work is done

a more powerful engine does work faster than a less powerful one 

power (W) = energy transferred (J) / time (s)

power (W) = work done (J) / time (s)

energy can be transferred usefully, stored, or dissipated, but cannot be created or destroyed.

temperature - a measure of the kinetic energy that individual particles in a substance have

heat - the total amount of energy in a substance. it takes into account the mass of the substance, as well as its kinetic energy. heat energy will only travel from places that are hot to places that are cold

the bigger the difference in temperature, the faster the heat energy will transfer.

methods of energy transfer:

• conduction - energy transfer through solids due to vibration of particles 
• convection - when particles with a lot more heat energy in a liquid or a gas move and take the place of particles with less heat energy 
• radiation - transfer of heat energy through thermal radiation (infa-red) that travels in waves of electromagnetic radiation

lubrication

• energy is dissipated when friction occurs 
• lubricants can be used to reduce the friction between objects 

insulation 

• thick walls made from a material with a low thermal conductivity 
• cavity walls - inner and outer wall filled with foam reduces energy lost by conduction and convection 

• wind
  • no permanent damage to the landscape. no pollution
  • very noisy. stops when there is no wind
• solar
  
• geothermal 
• hydro-electricity
  •  
• bio-fuels 
• wave power 
• fossil fuels 
  •  
• nuclear