energy Flashcards
what is energy
energy is required for things to work
what is an energy store
energy stores are ways in which energy can be stored in a system
e.g. food and fossil fuels are chemical potential stores.
a book on a tall shelf is a gravitational potential store
a bullet is a kinetic store
7 types of energy
Nuclear
Internal
Chemical potential
Elastic potential
Kinetic
Gravitational potential
Elastic potential
NICEE KG
what is the SI unit for energy
Joule (J)
what determines more energy in a kinetic store
objects moving at higher speeds have more energy in the kinetic store
what determines more energy in a gravitational potential store
objects further from the ground have more energy in the gravitational potential store
what determines more energy in a elastic potential store
elastic objects being strecthed or compressed have energy in the elastic potential store
what determines more energy in a chemical potential store
chemical bonds have energy in the chemical potential store
what determines more energy in a internal store
objects of higher temperature have more energy in the internal store
what determines more energy in a nuclear store
nuclei in atoms have energy in the nuclear store
4 ways energy can be transferred from one energy store to another in four different pathways
- mechanically (by a force acting over a distance)
- by heating (as a result of a temperature difference)
- by propagation of waves (both electromagnetic and mechanical)
- electrically (by charges moving through a potential difference)
what form of energy transfer is this?
energy is transferred from a cup of hot tea to a spoon when the spoon is placed in it
heating
what form of energy transfer is this?
Energy is transferred from an athlete to a set of weights when she does work in exerting a force to lift them above her head
work done by a force
what form of energy transfer is this?
energy is transferred from a light bulb to the surroundings by electromagnetic waves(light)
waves
what form of energy transfer is this?
energy is transferred from an electric cell to a light bulb by an electriccurrent
electric current
what is the principle of conservation of energy
the principle of conservation of energy states that energy cannot be created or destroyed. Energy can be transferred from one store to another. The total energy of an isolated system is constant
isolated system meaning
no transfer of energy and matter in/out of the system (ie no interaction with its surroundings
Kinetic energy formula
Ek = 1/2mv^2
where
Ek = energy in the kinetic store (J)
m = mass of body (kg)
v = speed of the body (m/s)
work done by a force formula
W = Fs
where
W = work done by a constant force F (J)
F = constant force (N)
s = distance moved in the direction of the force (m)
potential energy formula
Ep = mgh
where
Ep = energy in the GP store
m = mass of the body (kg)
g = gravitational field strength (N/kg)(9.8)
h = height (m)
work done against gravity formula
W = F x h = mgh
(F = mg)
work done against against gravitational force = GPE
power definition
power is defined as the work done or energy transferred per unit time.
power SI unit
watt(W)
power formula
P = W/t =E/t
where
P = power(W)
W = work done(J)
E = energy transferred (J)
t = time taken (s)
one watt (W) definition
one watt (W) is defined as the rate of work done or energy conversion of one joule per second.
one watt = one joule / one second
1W = 1J s^-1 = 1J/s
concept of efficiency in an ideal machine
the total energy output is equal to its total energy input
in reality, the useful energy output of a machine is always less than the energy input
efficiency formula
efficiency = Useful energy output/total energy input x 100%
what are fossil fuels
fossil fuels have energy in the chemical potential stores.
when a fuel is burnt in air for cooking food, heat transfers from the chemical potential store of the fuel to the internal stores if the food and the surroundings
advantages of fossil fuels
- more reliable than other resources as fossil fuels do no depend on environmental factors
- relatively cheaper cost of production compared to other resources
disadvantages of fossil fuels
- non renewable energy resource
- environmental pollution from the gases produced during burning contributes to global warming
