Energy

Energy is the ability to do work – Work is a transfer of energy Energy is measured in joules (J) – 1 joule = work done to move an object 1 meter by 1 N

Kinetic NRG Energy of a moving object KE = 1/2mv 2 m = mass and v = velocity Square velocity first Double the mass, double the KE Double the velocity, quadruple the KE

Potential NRG Stored energy Gravitational potential energy PE = mgh m = mass g = gravity h = height Greater the height, more PE Greater the mass, more PE

Elastic potential energy – When an object is stretched or compressed – The more stretched, the more potential energy – The more compressed, the more potential energy

Can there be kinetic energy and potential energy at the same time? – Yes! – Mechanical energy = KE + PE motion position Do you think energy can be created or destroyed? – No! – So the total amount of energy at the beginning will be the same at the end

Forms of NRG Mechanical Thermal Chemical Electrical Electromagnetic Nuclear

Mechanical Energy associated with motion and position Sum of potential and kinetic energy

Chemical Energy stored in chemical bonds Bonds are broken, energy is released Examples – Chemical compounds, such as fuels – Food – Muscles

Electrical Associated with electric charges Batteries convert chemical energy into electrical energy

Electromagnetic Form of energy that travels through space in the form of waves Ex: light, X-rays, radio waves Often used for communication because they travel long distances

Nuclear Energy stored in atomic nuclei Nucleus held by strong and weak forces (Large amount of PE) Fission (split nuclei) Fusion (combine nuclei)

Thermal Potential and kinetic energy of atomic particles When atoms move faster, thermal energy increases and object becomes warmer

Energy Conversions Energy can be converted from one form to another What type of energy conversion takes place when lighting a match? Chemical: rxns in muscles allow you to move the match Kinetic: match is moving Thermal: heat produced by friction Chemical: rxn on match’s tip triggered by thermal energy Thermal: heat produced Electromagnetic: light produced

Conservation of Energy Energy cannot be created or destroyed, it can only be transferred Ex: Bike slowing – Kinetic NRG becomes thermal NRG – Friction between the bike and the ground/air – Lose kinetic NRG, gain thermal NRG, total NRG is the same Ex: Pole vault – KE  Elastic PE  Gravitational PE  KE (KE + PE) beginning = (KE + PE) end

Heat TOTAL amount of kinetic energy of particles Transfer of thermal energy because of temperature differences Moves from hot to cold objects

Temperature AVERAGE amount of kinetic energy of particles Measure of how hot or cold something is Use a thermometer Celsius and Kelvin scales Absolute zero = 0 K Object heats up, particles move faster

Thermal Contraction and Expansion If temp decreases, particles move slower and closer together, so object contracts If temp increases, particles move faster and farther away, so object expands

Thermal NRG Absorption Depends on color, texture, and exposed surface area Absorb more than emit = temp increase Emit more than absorb = temp decrease Absorb and emit the same amount = thermal equilibrium

Specific Heat Amount of heat needed to raise the temperature of one gram of an object one degree Celsius Lower specific heat = temp rises more when given a certain amount of energy Q = m x c x change in T or Q = mc∆T Q = heat gained or lost (J) m = mass (g) c = specific heat (SI unit: J/g ˚C) T = temperature (˚C)

Conduction Transfer of thermal energy with no overall transfer of matter Objects must be touching to transfer heat

Conductors – conduct thermal energy well – Most metals are good conductors because electrons move easily Insulators – conduct thermal energy poorly

Convection Transfer of thermal energy when particles of a fluid move from place to place Convection current – Warm air rises – Cool air sinks

Radiation Transfer of energy by waves moving through space All objects radiate energy – Heat lamps – Sun