energy transfers Flashcards
when energy is transferred to an object hows it transferred
when energy is transferred to one of the objects energy stores
what are the 4 energy stores
kinetic, thermal, chemical, gravitational potential, elastic potential, electrostatic, magnetic and nuclear
work done is another way of saying..
energy transfer
how can energy be transferred in four main ways
mechanically e.g. making an object move by exerting a force on it
electrically e.g. electrons moving around an electric circuit
heating e.g. heating up water in a kettle
radiation e.g. energy from the sun is transferred via light waves
if you lift a ball up high what energy are you transferring. Then if you drop the ball hows energy transferred
if i lift a ball up high your transferring energy mechanically from the chemical energy store in my arm to the balls gravitational potential store. if i drop the ball energy is transferred mechanically due to the force of gravity to the balls kinetic store
whats a system another word for
a system is just another word for a single object
what are closed systems
closed systems are systems where neither matter nor energy can enter or leave. The net change in the total energy of a closed system is always zero
whats the conservation of energy principle
energy can be transferred usefully,stored or dissipated but can never be created or destroyed
whats dissipated energy
another word for wasted energy
anything which is moving has energy in its..
kinetic energy stores. if the object speeds up energy is transferred into that store, if the object is slowed down energy is transferred away
a moving object will have a … and…
a moving object will have a mass (kg) and velocity (m/s) (speed in a given direction)
equation for kinetic energy and triangle
Ek = 1/2mvsquared
Ek on top of the triangle, 1/2 on the left bottom, m next to 1/2 and vsquared on the right
whats kinetic energy measured in
joules (J)
how to get from g to kg
divide by 1000
how to get from kg to g
x 1000
what does lifting an object cause a transfer of…
lifting an object in a gravitational field requires work. this csauses a transfer of energy to the gravitational potential energy (g.p.e) store
whats the symbol for energy transfer
Ep
what 3 things does the amount of energy transferred (Ep) depend on
the objects mass (m). this is ALWAYS in kg (so convert when needed)
the strength of the gravitational field (on earth that is 9.8N/Kg, this means that for every 1kg of mass, gravity pulls down on that object with a force of 9.8N (g)
the height e.g. how high the object is lifted (h) this is always in metres (so convert if needed)
whats the equation from gravitational potential energy (j) and units
how do u put it in a triangle
EP = mgh
m=kg g=N/Kg h = m
Ep at the top m on the bottom left g in the middle bottom h on the right
e.g. a 50 kg mass is raised 6.0m above the ground. How much energy was transported to the g.p.e store if the gravitational field strength was 9.8N/Kg
50x9.8x6.0
=2490J
energy lost from the g.p.e store =
energy lost from the g.p.e store - energy gained in the kinetic energy store
Ep =?
Ep = Ek
a man with a mass of 65kg falls from a height of 2m. If the gravitational field strength is 9.8N/Kg how fast is he falling
ep = mgh
65x9.8x2=1247J
ek = 1/2mvsquared
=6.2m/s
definition of specific heat capacity
specific heat capacity is the amount of energy needed to raise the temperature of 1kg of a substance by 1degreeC
change in thermal energy equation and how to put it in a triangle
Change in thermal energy = mass x specific heat capacity x change in temperature
ΔQ = m × c × ΔT
Ee is the same as
Ek
whats the experiment to investigate the specific heat capacity of a solid material e.g. copper
you first measure the mass of the block of material.once this is done u wrap the block in an insulating material to reduce heat energy transfer to the environment. inserted into the block is a thermometer and an immersion heater. the heater is connected to a power supply which is set to 10v. when power supply is switched on the immersion heater warms up heating the block up.take an initial temp reading,switch the hater on and then leave it for a set period of time e.g.10 mins.after this time u measure the temp of the block again.
this current does work on the heater transferring energy electrically from the power supply to the heaters thermal store.the energy is then transferred to the thermal store of the block by heating causing by the temp to increase
whats power
power is the rate of energy transfer, or the rate of doing work
whats conduction
the process by which vibrating particles transfer energy to neighbouring particles
thermal conductivity definition
measure of how quickly energy is transferred through a material this way. the higher the thermal conductivity the quicker the energy is spread out across an object via conduction
whats a thermal insulator and thermal conductor
a material with a high thermal conductivity is known as a thermal conductor. A material with a low thermal conductivity id known as a thermal insulator
what are things u can use to reduce the amount of energy lost from a building
loft insulation
hot water tank jacket
double glazing
cavity wall insulation
draught-proofing
whats loft insulation
fibreglass is an insulating material made of thin strands of glass that trap pockets of air. a thick fibreglass wool laid out across the whole loft floor reduces conduction to the attic space,as the material it reduces the energy transfer by convection, by preventing convection currents from forming
whats double glazing
double glazed windows work in the same way as cavity walls they have an air gap between 2 sheets of glass to prevent energy transfer by conduction through the windows
whats draught proofing
draught excluders or strips of foam or plastic around doors and windows stop draughts blowing in and out, and reduce energy transfer by convection
whats hot water tank jacket
putting fibreglass wool around a hot water tank reduces the energy transfer by conduction from the tanks thermal energy store in the same way as loft insulation
whats thick curtains do for insulation
big bits of cloth over the window create an air gap between the room and the window,stopping hot air reaching the glass by convection. they also reduce energy transferred by convection
how to investigate how effective various materials are as thermal insulators using an experiment
boil water in a kettle. put some of it into sealable container to a safe level. measure mass of the water in the container and use a thermometer to measure the initial temp of water. seal container + leave for 5 mins meausre this time. then remove lid + measure final temp of water. pour away water and allow container to cool to room temp. repeat but each time wrap container in diff material
