P1 - conservations and dissipation of energy

Energy store + definitions

ways that energy is transferred

• mechanically - when a force acts on an object

• electrically - a charge moving through a potential difference

• heating by particles - energy is transferred from a hotter one to a colder one

• heating by radiation -energy transferred by electromagnetic waves

what happens when a object is projected upwards?

chemical store ---→ kinetic store ----→ gravitational store

what happens when a moving objects hits an obstacle?

chemical store ----→ kinetic store ----→ thermal store

what happens when a vehicle is being accelerated with constant force?

chemical store ----→ kinetic store (thrust)

what happens when a vehicle slows down?

chemical store --→ thermal stores

what happens when boiling water in a kettle?

electrical store ---→ thermal store (of kettle) ---→ thermal store (of watre)

equation of kinetic energy

kinetic energy = 1/2 x mass x speed^2

J = 1/2 x kg x m/s^2

what is a closed system?

a closed system is a system where no energy transfers take place out of or into the energy stores of the system

what happens to the energy in a closed system, after being transferred?

the total energy of the system stays the same , before and after

what is work done?

energy transferred

work done equation

work done (J) = force applied (N) x distance moved along the line of action of the force (m)

change in objects gpe equation

change in objects gpe = weight x change in height

change of gpe equations

change of gpe = mass x gravitational field strength x change of height

gpe equation

gpe = mass x gravitational field strength x height

gpe on earth

the gravitational field strength on the earth is approximately 9.8 N/kg

elastic potential energy equation

elastic potential energy = 1/2 x spring constant x extension of spring^2

useful energy

useful energy is energy transferred to where it is wanted and in the way, it is wanted

wasted energy

wasted energy is energy that is not usefully transferred

efficiency equation

efficiency = useful output energy/ total input energy

efficiency of appliance

efficiency of an appliance = useful power out/ total power in x (100)

change in thermal energy

change in thermal energy = mass x specific heat capacity x change in temperature

power

power = energy transfer/ time

power equation

power = work done/ time

power wasted

power wasted = total power in - useful power out