Topic 1 – Energy fundamentals Flashcards
what is kinetic energy
how much kinetic energy does a stationary object have?
energy stored in moving objects
none
whats the equation for kinetic energy
kinetic energy = 0.5 x mass x speed^2
what is elastic potential energy
when we stretch a spring were applying a force to change its length (doing work) we are putting in energy to stretch the spring, the stored energy is elastic potential energy
whats the equation for elastic potential energy (g)
elastic potential energy = 0.5 x spring constant x extension^2
what happens to a graph if you overstretch a spring
graph won’t be directly proportional as springs been stretched beyond limit of proportionality
extension must always be in:
metres
what is gravitational potential energy
the energy stored in an object due to its position above the earths surface
this is due to gravity acting on an object
how to calculate gravitational potential energy
gpe = mass x grav field strength x height
whats thermal energy
the energy stored due to an objects temperature
whats the law of conservation of energy
energy can be transferred usefully, stored or dissipated but it cannot be created or destroyed
whats a system
an object or group of objects
in a CLOSED system energy_____
cannot enter or leave
what are the energy transfers in a pendulum?
mass has maximum GPE, then its transferred to KE , then mass has maximum KE at bottom (mid swing) then its transferred back to GPE where it has max GPE one more
whats an issue with the pendulum example?
does not consider friction
what does friction cause (in terms of energy transfer)
causes energy to be transferred to thermal energy
energy has been dissipated as thermal energy is less useful
where is friction on the pendulum?
friction on the fixed point
friction as the pendulum pass through the air particles
what does friction cause the pendulum to do
gradually swing with less energy and eventually stop
how can we reduce unwanted energy transfers in a pendulum
remove friction by:
using a lubricant on fixed point
removing air particles from around pendulum
what are the energy changes in a bungee jumper
GPE at start,,, energy is transferred to KE as man falls.
KE store is at it max when rope JUST starts to tighten, KE store of fully extended rope is 0 (JUMPERS NOT MOVING)
all energy is transferred to elastic potential energy
ElP —> KE as rope coils
KE—-> GPE during ascent
at top, all is GPE
why will bungee jumper never return back to his original position?
energy is dissipated as thermal energy
(friction w air particles & stretching effects of bungee rope which arent fully elastic)
what is work done
when energy is transferred from one store to another
what does mechanical work involve
using a force to move an object
whats electrical work
a current transferring energy
whats the equation for work done?
work done (J) = force x distance (m)
what is power
the rate at which energy is transferred or at which work is done
what are the equations for power (W)
energy transferred (J) / time (s)
or
work done (J) / time (s)
1 watt is the same as____
1 J per second
whats the equation for effienciency
useful energy output / total energy output
or
useful power output/ total power INPUT