energy - physics topic 4 revison Flashcards
(18 cards)
what is the definition of the conservation of energy?
the total amount of energy is always same- cannot be created or destroyed, just changed from one type to another
what are stores?
the places where energy is gathered (always an equation)
what is a pathway?
how energy moved from one store to another
what are the 8 stores and what are their meanings?
- chemical –> released by chemical reactions
–> food/fuel - gravitational potential –> have to lift it
- kinetic —> movement
- thermal –> heat
- elastic –> stretch/squash/twist it
- nuclear –> break the nucleus apart
–> pushing two together - magnetic –> attraction and repulsion of electric fields
what are the four pathways and their meanings?
- waves –> light, infrared etc.
- particles –> conduction etc.
- electricals –> circuits
- mechanical –> lots of different things going on
what are useful transfers?
when the energy is used for the purpose of the object
what are waste transfers?
when we lose energy to stores we don’t want
what does energy allow to happen?
it allows EVERYTHING to happen. when things happen, energy is transferred
what is efficiency?
the measure of how much energy is used usefully
what is the equation for efficiency?
energy transferred usefully
—————————————- x 100 (to make it a
percentage)
total energy put in
what does a sankey diagram show?
a sankey diagram shows energy flow.
for example, if an electrical fan had 100J of energy and 80J was used for movement, the sankey diagram would show the store as electrostatic, but shows it flowing through the electrical pathway. 80J of it goes straight ahead to be used as kinetic energy (useful), and 20J goes off to the side as thermal energy (waste)
forces can change the energy in a store. what are the forces which do this and their corresponding stores?
- speed (kinetic store)
- height (gravity store)
- shape (elastic store)
- bow a string (instrument) (kinetic sore)
what is work?
it measures how much energy is transferred, and depends on the amount of force and the distance you apply it for
what is the equation for work?
work done (J) = force x distance the force is applied for
what is power?
the rate of energy transfer (how quickly work is done)
what is the equation for power and its units?
power = work/energy (J)
J/S or ————————
watts (W) time (s)
what is the order from most to least power and why, out of walking up the stairs, lifting stand bags and step ups?
the order from most to least is running up the stairs, step ups then lifting sandbags. this is because for the stairs and step ups you need to lift up your entire body weight which weighs a lot more than the bag.
the stairs used up more energy because the activity is shorter so you don’t need to conserve any energy, whereas for the step ups, you need to conserve your energy to be able to use it through the longer activity
what does the particles/radiation pathway show?
these look at much anergy is transferred to an object as heat. specific heat capacity allows us to measure energy and power transferred this way
