TOPIC 1 - ENERGY Flashcards
Name the energy stores.
Thermal Kinetic Gravitational potential Elastic potential Chemical Magnetic Electrostatic Nuclear
How can energy be transferred?
Mechanically - force, doing work
Electrically - work done by moving charges
Heating or radiation - light or sounds
What is a system?
A single object eg the air in a piston or a group of objects eg two colliding vehicles that you’re interested in.
What happens when a system changes?
Energy is transferred. It can be transferred into or away from the system, between different objects in the system, or between different types of energy stores.
What is a closed system?
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.
What is work done?
Another way of saying the energy transferred. Work can be done when current flows or by a force moving an object.
Explain the kinetic energy store.
Anything that is moving has energy in its kinetic energy store. Energy is transferred to this store when an object speeds up and is transferred away from this store when an object slows down. The energy in the kinetic energy store depends on its mass and speed. The greater it’s mass and the faster it’s going, the more energy there will be in the kinetic energy store.
What is the equation for kinetic energy?
Kinetic energy = 1/2 mass x speed (v) squared
Talk about the gravitational potential energy store.
Raised objects store energy in the gravitational potential energy store. Lifting an object in a gravitational field requires work. This causes a transfer of energy to the gravitational potential energy store of the raised object. The higher the object is lifted, the more energy is transferred to this store. The amount of energy is a gpe store depends on the objects mass, height and the strength of the gf the object is in.
What is the equation to find the change in energy in an object’s gravitational potential energy store?
Gravitational potential energy = mass x gravitational field strength x height.
Talk about elastic potential energy stores.
Stretching or squashing can transfer energy to elastic potential energy stores. This is as long as the limit of proportionality has not been extended.
What is the equation to find the energy in the elastic potential energy store?
Elastic potential energy = 1/2 spring constant x extension squared
What is the specific heat capacity?
THE AMOUNT OF ENERGY NEEDED TO RAISE THE TEMPERATURE OF 1KG OF A SUBSTANCE BY 1 DEGREES CELSIUS.
Means how hard it is to heat something up. More energy needs to be transferred to the thermal energy store of some materials to increase their temperature than others.
Materials that need to gain lots of energy in their thermal energy stores to warm up also transfer loads of energy when they cool down again. They can ‘store’ a lot of energy.
What is the equation for specific heat capacity?
Change in thermal energy = mass x specific heat capacity x temperature change.
What is the practical to investigate specific heat capacity?
To investigate a solid material (eg copper) you will need a black of the material with two holes in it (for the thermometer and heater to go into)
Measure the mass of the block, the wrap it in an insulating layer (eg a think layer of newspaper) to reduce energy transferred form the block to the surroundings. Measure the initial temperature of the block and the the potential difference (V) of the power supply to be 10V. Turn on the power supply and start a stop watch. The current does work on the heater, transferring energy electrically from the power supply to the heater’s thermal energy store. This is the transferred to the material’s thermal energy store by heating, causing the materials temperature to increase.
Take readings of temperature and current every ten minutes. (The current shouldn’t change as the block heated up). Once you have collected enough readings turn off the power supply. You can calculate the power supplied to the heater using the equation power = potential difference x current. You can use this to calculate how much energy has been supplied to the heater using E = Pt. you can the plot a graph of energy transferred to the thermal energy store against temperature. Find the gradient of the straight part of the graph. The specific heat capacity is
1/(gradient x mass of the block).
What is the conservation of energy principle?
Energy is always conserved. When energy is transferred between stores, not all of the energy is transferred usefully into the store. Some energy is always dissipated when an energy transfer takes place. Dissipated energy is sometimes called wasted energy because energy is being stored in a way that is not useful.
Eg in mobile phones some energy is dissipated in the transfer to the thermal energy energy store of the phone.
What is power?
The rate of energy transfer, or the rate of doing work. Power is measured in watts - one watt = 1 joule of energy transferred per second.
What are the two equations to calculate power?
Power = energy transferred/time
Power = work done/time
What is conduction?
Conduction is the process where vibrating particles transfer energy to neighbouring particles.
It occurs mainly in solids.
Energy transferred to an object by heating is transferred to the thermal store of the object. This energy is shred across the kinetic energy stores of the particles in the object. The particles vibrate more and collide with each other. These collisions cause energy to be transferred between the particles kinetic energy stores. This is conduction.
What is thermal conductivity?
A measure of how quickly energy is transferred through a material in this way. Materials with a high thermal conductivity transfer energy between their particles quickly.
What direction is heat transfer?
Hot to Cold.
What is convection?
Convection is where energetic particles move away from hotter to cooler regions.
It can happen in gases and liquids. Energy is transferred by heating to the thermal store of the liquid or gas. This energy is shared across the kinetic energy stores of the gas or liquids particles. As these particles are able to move, when you heat a region the particles move faster and the space between them increases. This causes the density of the region being heated to decrease. As liquids and gases can flow, the warmer and less dense region will rise above the denser, cooler regions. If there is a constant heat source, a convection current can be created.
How do radiators create a convection current?
Energy is transferred from the radiator to the nearby air particles by conduction (the air particles collide with the radiator surface). The air by the radiator becomes warmer and less dense as the particles move quicker. This warm air rises and is replaced by cool air. The cooler air is then heated by the radiator. At the same ti,e, the previously heated air transfers energy to the surroundings. It cools, becomes denser and sinks. This cycle repeats, abusing a flow of air to circulate around the room - this is a convection current.
How can lubrication reduce unwanted energy transfer?
Lubrication reduces frictional forces. Whenever something moves, there is usually at least one frictional force acting against it,this causes energy 8 the energy system to be dissipated eg air resistance can transfer energy from falling objects kinetic energy store to its thermal energy store. For objects that are being rubbed together, lubricants can be used to reduce friction between the objects surfaces when they move. Lubricants are usually liquids, for example oil, so they flow easily between objects and coat them.