energy conservation and dissipation Flashcards
conseravtion principle
energy cant be made or destroyed
examples of energy stores
kinetic
thermal
graviational and elastic pot
ways energy can be tranferred
thermal
mechanical
sound
electrically
whats an open system
the system of matter can lose and gain energy from its surroudnings
whats a closed system
neither matter nor energy can enter or leave change stays at zero
peneglum energy example
at the height of its swing it has no kinetic energy but max grav pot as it reaches the middle kinetic is max but grav is at zero. it stops swining due to it being a closed system and losing energy to air resistence
what is work done
th energy tranferred to something
work done equation
wd
force x distance
where does work done against fricatin go to
thermal energy stores
earths grav field strength
9.8N
what si weight
grav field strength x mass
grav pot equation
grav pot =
height x weight (mass x grav field strength0
Whats kinetic energy
energy stored in moving objects
kinetic equation
ke
1/2 x m x s2
whats elastic pot
work done on an object to stretch it, it stores elastic pot
elastic equation
EP= 1/2 x k x e2
1/2 x extention2 x spring consant
what is wasted energy
when energy is wasted on things that arent their intention, theure dissipated (spread out) in the surroudnings
eg in a plane kinetic for movement and grav pot for flying is useful, but thermal and sound is not
efficiency equation
useful output =
efficiency x total power
as energy dissipates….
it becomes less useful. eg heated pipes lose energy to radiators which lose it to the air
ways to improve efficiency
lubricate to reduce friction
streamline shapes for less air resistence
use wires with less electrical resistence
ways energy to the home is supplied
gas
oil
electricity
what is power
rate of energy transferred/ work done per sec
power equation
energy tranferred/ work done =
power x time
whats power measured in
watts
explain energy tranfer in a bungee jumper
begins with it all in gravitational pot, as the person falls the kinetic increases and as the rope tightens the kinetic slows and goes to the elastic potential, they rise back up losing elastic to kinetic and kinetic to grav pot, continue this until it is all lost to surroundings via thermal as the rope stretches
things that affect grafitational pot between two objects
- distance between
- masses
whats a thermal energy store
- kinetic
- potential
