Energy Flashcards
Consevation of Energy
Energy cannot be created or destroyed, but only can be transferred from one energy store to another energy store.
Types of energy stores
Kinetic Chemical Thermal Gravitational potential Magnetic Electrostatic Elastic potential Nuclear
Energy transfer pathways
Mechanical- when a force is involved
Electrical- when electricity is involved
Heating- when there is a change in temperature
Radiation- by other EM waves
Energy Transfer Example:
Start- Unlit Match
End- Lit Match
The energy is stored in a chemical store in the match. It is then transferred to a thermal energy store though a mechanical pathway.
Energy Transfer (work done) Equation
W = Fs
This means:
Force [N] x Distance [m] = Work done [J]
Gravitational Potential Energy (GPE)
The energy that a body has due to its height above the ground.
GPE Equation
GPE = m.g.h
Change in GPE = mass x gravitational field strength x change in height
Kinetic Energy (KE) Equation
KE = ½mv²
KE Example
KE= ? KE= ½mg² m= 1200kg KE= ½ x 1200 x (20)² v= 20 KE= 240x10³J
GPE Example
GPE= ? GPE= m.g.h m= 12kg GPE= 12 x 9.81 x 3.4x10³ g= 9.81 N/kg GPE= 4.0x10^5 h= 3.4 km
Wasted energy
Energy that is not usefully transferred.
Useful energy
Energy transferred to where it is wanted in the way that is wanted.
Efficiency
Useful energy transferred by a device ÷ total energy supplied to the device.
Dissipated energy / dissipation of energy
The energy that is not usefully transferred and stored in less useful ways.
Hooke’s Law
The extension of a spring is directly proportional to the force applied, as long as its limit of proportionality is not
exceeded.
