1 - Energy Flashcards
What is kinetic energy? (KE E Ph)
the energy stored in moving objects. Stationary objects have no kinetic energy.
What is the equation for kinetic energy and what are the units? (KE E Ph)
Ek = 0.5 x m x v2
J = 0.5 x kg x m/s2
What energy store do cars run on? (KE E Ph)
chemical energy store in petrol. a chemical reaction takes place and some of this energy is converted into the kinetic energy store.
What is the distance called when we apply a force on a spring and it streches? (EPE E Ph)
the extension
What is the symbol for extension in Elastic Potential Energy? (EPE E Ph)
e
What is the graphical relationship between the extension and the force applied to a spring? (EPE E Ph)
They are proportional however if we apply too much force then they are no longer proportional. This point is called the limit of proportionality and the spring will no longer return to its original shape once the force is released.
What is the limit of proportionaility? (EPE E Ph)
The point in which two things (extension and force) are no longer proportional to each other.
What type of energy store is in a stretched spring? (EPE E Ph)
Elastic Potential Energy
What is the equation for Elastic Potential Energy and what is its units? (EPE E Ph)
Ee = 0.5 x k x e2
J = 0.5 x N/m x m
What is Gravitational Potential Energy? (GPE E Ph)
the energy stored in an object due to its position above the earths surface which is due to the force of gravity acting on an object
What is the equation for gravitational potential energy and what are the units? (GPE E Ph)
Ep = m x g x h
J = kg x N/kg x m
What is the specific heat capacity of a substance? (SHC E Ph)
the amount of energy required to raise the temperature of 1kg of the substance by 1 degree C.
What is thermal energy? (ETP E Ph)
the energy stored due to an object’s temperature.
What is the law of conservation of energy? (ETP E Ph)
energy can be transferred usefully, stored or dissipated but it cannot be created or destroyed.
What is a system? (ETP E Ph)
An object or a group of objects
What is a closed system? (ETP E Ph)
no energy can enter or leave.
What is the energy transfer of a pendulum in a closed system? (ETP E Ph)
When the mass swings all the way to the left, it has the maximum GPE. When it swings down to the middle, the GPE transfered to KE. At the middle the mass has the maxiumum KE. When the mass swings up towards the right, the KE is transferred to GPE. When the mass is all the way to the right, it has the maximum GPE again.
However some of the energy is being dissapated due to the friction with the air particles. This will cause the energy to be converted into thermal energy and will mean that the pendulum will eventually come to a stop.
What are the energy stores and transfers throughout the process of a bungee jumper falling? (BJ E Ph)
- all the energy at the start of the jumps is in the store of gravitational potential energy.
- As the jumper falls, energy is transferred from the gravitational potential energy store to the kinetic energy store.
- When the bungee rope just begins to tighten, the kinetic energy store is at its maximum
- When the rope is fully extended, the kinetic energy store is 0. They are no longer moving.
- All of the energy has been transfered to the elastic potenital energy store
- the bungee rope now recoils and energy is transered from the elastic potenital energy store back into the kinetic energy store
- during the ascent, energy transferes from kinetic back into gravitational
- at the top of the ascent, all of the energy is now gravitational
key point: the jumper never returns back to its original position because energy has dissipated as thermal energy. due to friction with air particles and stretching effects in the bungee rope which is not fully elastic
What is work done and what are the two different cases of it? (WDF E Ph)
Work is done whenever energy is transfered from one store to another
1. mechanical work - involves using a force to move an object
2. electrical work - involoves a current transfering energy
How do you calculate work done and the units? (WDF E Ph)
Work done (J) = Force (N) x Distance (m)
What is the definiton of power? (CP E Ph)
the rate at which energy is transferred or the rate at which work is done.
What are the units in this equation: (Power = Energy Transferred / Time) (CP E Ph)
Power (W) = Energy Transferred (J) / Time (s)
What are the units in this equation: (Power = Work Done / Time) (CP E Ph)
Power (W) = Work Done (J) / Time (s)
What does efficiency tell us? (E E Ph)
What fraction of energy we put into an applience is transferred to useful forms of energy.
Why are plastic kettles more energy efficient than a metal pan? (E E Ph)
Metal is a good conductor of heat so some of the thermal energy will escape through the metal
Some thermal energy is used by heating the bottom of the metal pan so we put the heating agent inside the water in the kettle.
The higher the thermal conductivity of a material, :(CB E Ph)
the higher the rate of energy transfer by conduction across that material
What are the structural features of walls in the uk to slow down heat loss from buildings? (CB E Ph)
Internal breezeblock wall on the inside, insulating material with low thermal conductivity, and external brick wall.
Thick walls as well
What are the structural features of windows in the uk to slow down heat loss from buildings? (CB E Ph)
double glazed windows with low thermal conductivity
What are the structural features of roofs in the uk to slow down heat loss from buildings? (CB E Ph)
loft insulation with low thermal conductivity
What is the specific heat capacity? (RP1 E Ph)
the specific heat capacity of a substance is the amount of energy required to raise the temperature of 1kg of the substance by 1C.
How do you measure the Secific Heat Capacity of a substance (oil)~ required practical (RP1 E Ph)
- place a beaker on a balance and press 0.
- add the substance and record the mass of the oil
- place a thermometer and immersion heater into the substance
- read the starting teperature of the oil
- wrap the beaker in insulating foam to reduce thermal energy transfer to the surroundings
- connect a joulemeter to the immersion heater which tells us how many joules of electrical energy pass into the immersion heater
- leave the setup for around 30 minutes. which will allow the temperature to rise enough so that we can accuratly read it on the thermometer
- read the total number of joules of energy that passed into the immersion heater and the final temperature of the oil.
What are the sources of inaccuracy in the required practical for specific heat capacity? (RP1 E Ph)
- thermal energy passing out of the beaker into the air ~ use an insulator with a lower thermal conductivity
- not all thermal energy passing into the oil ~ ensure that the immersion heater is fully emerged
- incorrectly reading the thermometer ~ une an electronic temperature probe
- thermal energy may not be speead through the oil ~ stir the oil
What is the method for comparing the effectivness of different materials as thermal insulators. and what are the variables (RP2 E Ph)
- place a small beaker inside a large beaker
- use a kettle to boil some water and transfer 80cm3 of hot water into the small beaker
- use a piece of cardboard as a lid for the larger beaker and it must have a hole for a thermometer
- place the thermameter through the hole in the lid and the bulb of the thermometer must be in the hot water
- record the starting temperature of the water and start a stopwatch
- record the temperature of the water every three minutes for 15 minutes
7 repeat the experiment with the same volume of hot water however this time we use an insulating material to fill the gap between the two beakers (test a
range of different materials here but use the same mass every time)
Independent variable : type of insulating material
dependent variable : temperature
control : volume of water and the mass of insulating material, the starting temperature the same - record all results in a table
What is the method for comparing the thickness of a material effects the thermal insulation and what are the variables (RP2 E Ph)
- a beaker containing 80cm3 of hot water
- measure the temperature of the water every 3 minutes for fifteen minutes
- repeat the experiment but wrap 2 layers of newspaper around the beaker
- repeat the experiment 2 more times but use for layers and then six layers of newspaper
independent :number layers of newspaper
dependent : temperature
control : strarting temperature of water and the volume of water
