- Created by: jeban02
- Created on: 19-05-20 13:14
Energy Stores and Carriers
There are eight different energy stores:
- Thermal Energy Store
- Kinetic Energy Store
- Gravitational Potential Energy Store
- Elastic Potential Energy Store
- Chemical Energy Store
- Magnetic Energy Store
- Nuclear Energy Store
- Electrostatic Energy Store
There are four different carriers (ways that energy is transferred from one store to another)
- Mechanical carriers (forces doing work)
- Electrical carriers (work done by moving charges)
- Radiation (light or sound)
The Law of Conservation of Energy
The Law of Conservation of Energy tells us that:
Energy is not created or destroyed, but it is transferred from one store to another, usefully or non usefully. If it stored non usefully, then it is dissipated into the surroundings.
- A system is a group of objects that interact with each other.
- A closed system is where neither matter nor energy can leave the system. The net chang ein the total energy of a closed system is always 0.
For example, if we are to throw a ball onto the ground, the ball will not return to the same height as it did on the first bounce back, on the second bounce back. This is because the resistive forces such as friction cause the ball to lose its kinetic energy to forces such as thermal energy store. This is why a bouncing ball will eventually stop bouncing, as all of its kinetic energy has been converted into thermal energy store and dissipated into the surroundings.
Kinetic Energy Store
Kinetic Energy is the energy that is stored in moving objects, therefore stationary objects have no kinetic energy.
- Energy is transferred to this store, when an object speeds up, and away from this store when an object slows down.
- It can be calculated by using this equation, which we must learn:
Kinetic Energy (J) = 0.5 x mass (kg) x velocity squared (m/s)
Ek = 0.5 x m x v2
Gravitational Potential Energy Store
Gravitational potential energy is the energy stored in an object due to its position above the surface of the Earth. This is due to the force of gravity acting on an object.
- The gravitational field strength at the surface of the Earth is 9.8 N/kg.
- This varies on different planets.
- We can work out the GPE using this equation:
Gravitational Potential Energy (J) = Mass (kg) x Gravitational Field Strength (N/kg) x Height (m)
Ep = m x g x h
Gravitational potential energy increases whwn an object is being lifted. For example, if we are lifting an object onto the shelf, the chemical energy store in our muscles is transferred to the gravitational potential energy store of the object.
The same applies when an object falls. The GPE decreases as it decreases in height, and it is converted into elastic potential energy when the object collides with the floor, and vibrations which are carried away by the sound carriers, and the thermal energy store is increased due to friction which dissipate into the surroundings.
Elastic Potential Energy Store
When a spring is stretched, two deforming forces are applying a force to change the length of the spring. Applying a force like this is called "doing work." Energy is put in to stretch the spring by doing this work.
The energy from applying the deforming forces is stored in the spring and the name of that energy is called Elastic Potential Energy Store.
It can be calculated using this equation:
- Elastic Energy (J) = 0.5 x Spring constant (N/m) x Extension squared (m)
Ee = 0.5 x k x e2
Extension (m) is directly proportional to the force (N) applied, as long as it is below the limit of proportionality. If the spring is being compressed instead of being extended, we can apply compression as the extension in the equation - it must be squared.
Energy Transfers - Pendulum
Energy can be transferred in many ways, this is an example of a PENDULUM.
The system we are considering includes the fixed point from where the string is attached, the pendulum mass, the spring, and the air particles surrounding it. It is a closed system.
- When the pendulum swings the highest, it has the maximum gravitational potential energy.
- When the pendulum swings to the middle, where it is its bottom point, the gravitational potential energy is transferred to kinetic energy, which is at its highest, as that is the point where the mass of the pendulum will travel the fastest.
- As the mass travels back up, the kinetic energy store of the mass has been transferred to the gravitational potential energy store of the mass.
Because there are air particles that the ball will collide with, they will get heated and therefore, some of the energy will be transferred into the thermal energy store, and it will be dissipated into the surroundings. Also, there will be fritction created at the fixed point from where the string is attached. That is why, at one point all of the energy will be transferred to the thermal energy store, and the ball will stop moving.
We can lubricate and streamline to reduce unwanted energy transfers such as this.
Energy Transfers - Bungee Jumper
Energy can be transferred in many ways, for example, we can observe the energy changes in a Bungee jumper.
- At top of the mountain: Highest Gravitational energy potential store.
- When he jumps first: GPE converts to Kinetic Energy store.
- When rope begins to tighten: Kinetic energy is now at its maximum point
- When rope fully extends: Kinetic energy converts into elastic potential energy of rope.
- When rope recoils: Elastic potential energy of rope converts back to kinetic energy store of the jumper.
- Moving upwards again: Kinetic energy store of the jumper converts to GPE of jumper.
There are a few notes about this:
- The bungee jumper will never return to the same height, as some of the energy is dissipated into the surroundings as thermal energy store when the jumper collides with air particles.
- The rope is not 100% elastic, it is made of other fibres too.
Work Done by a Force
Work is done whenever energy is transferred from one store to another.
Mechanical work involves using a force to move an object.
Electrical work involves a current transferring energy.
· Work done (J) = Force (N) x Distance (m)
Power is the rate at which energy is transferred, or the rate at which work is done. There are two equations for power:
- Power (W) = Energy transferred (J) ÷ Time (s)
- Power (W) = Work Done (J or Nm) ÷ Time (s)
The unit for power is the Watt (W).
1 Watt is an energy transfer (or work done) of 1 J per 1 second. The more Watts an object has, the more powerful it is - i.e. the more energy it can transfer in a short amount of time.
For example, if two cars that are identical in every way apart from power are having a race, the more powerful one will reach the finish line first, because it can do the same work as the slower car but in a shorter amount of time. They will both exert the same energy, but the faster one will do it in a shorter time, which gives it a higher power rating.
Efficiency is how useful a device is - meaning, how much of the energy that is transferred is put to useful means, compared to how much of it has been dissipated into the surroundings.
The less energy that is wasted, the more efficient a device will be.
Most devices are not 100% efficient, as a fraction of the energy will always go to the thermal energy store of the surroundings, as friction is inevitable in some cases, except electrical heaters, because the thermal energy released then is useful. Therefore electrical heaters are 100% efficient.
The equation for Efficiency is:
- Efficiency = Useful Output Energy Transfer (J) ÷ Total Energy Input Transfer (J)
- Efficiency = Useful Power Output (W) ÷ Total Power Input (W)
We can increase the efficiency of an object by insulating it, lubricating it, or streamling it.
It has no unit, as it is a percentage or a decimal.
Required Practical - Thermal Insulators
The insulating material is the indepndent variable, because it is being changed each time (but the same mass is kept to keep the experiment fair).
The temperature is the dependent variable as it is being measured each time the insulating material is changed.
The mass of the insulating material and the volume of the water and beaker size is kept constant.
We must also keep the starting temperature of the water the same for each experiment.
For this experiment, we plot cooling curves for the didfferent insulators. The water that will cool down the most slowliest, will be the one that has been insulated effectively, as it took longer for the thermal energy to leave beaker and dissipate into the surroundings as thermal energy that is useless.
This experiment can be repeated, but by increasing the thickness and measuring at intervals, which can show us how the thickness effects how quickly the energy is lost.
Thermal Insulators - Method
This is the method for the practical on the reverse of this card:
1) In a beaker, fill in water at a certain temperature, and place a lid with a hole on the top for the thermometer to go inside. Measure the mass of the water in the container, and record the temperature of the water to begin with – make sure that this is the same each time you change out for a different insulating material.
2) Every 2 minutes, measure the temperature of the water, and repeat this 5 times. Record the results.
3) Pour away the water in the container, and let the container cool down. Now, fill in the same mass of water as before, at the same starting temperature as before, but now, add an insulating material around the water.
4) Every 2 minutes, measure the temperature of the water, and repeat this 5 times. Record the results.
5) Now, rinse out this water, and let the container cool down. Fill in the same mass of water, at the same starting temperature, and put another insulating material around the water – but keep it at the same mass as the other insulating material.
Energy Resources and their Uses
Non Renewable Energy Resources
- Non renewable sources are energy sources that are not being replenished as they are being used up, they are finite and will run out one day.
- They provide about 80% of energy in the world.
- They are: Coal, Oil and Gas.
There are certain advantages to them:
- They are versatile.
- They are reliable and can produce a large amount of energy at a given time.
- They are abundant and relatively cheap.
There are certain disdvantages to them:
- They produce carbon dixiode, which contributes to global warming.
- They produce other pollutants such as sulphur dioxide, which causes acid rain.
- They are non-renewable and will run out one day.
Nuclear Power is non-renewable. Nuclear power plants run on the elements uranium and plutonium.
The advantages of a nuclear power plant are:
- It releases no carbon dioxide, therefore, it does not contribute to climate change.
- It is extremely reiable, because it generates a lot of energy when we want it.
The disadvantages of a nuclear power plant are:
- Nuclear power plants contain higly dangerous radioactive materials. If there was to be an accident, then these materials could be released into the environment - that would be dangerous.
- Decomissioning or dismantling a nuclear power plant takes many years and it is very expensive.
- During its life, it produces highly dangerous radioactive waste which must be stored for thousands of years before its safe.
Biomass is a renewable fuel as long as it comes from a sustainable source such as forest residue, animal matter and waste - derived from the chemical store.
- It is an alternative to fossil fuels, and it is burned to produce a steam to run the turbines.
- It is renewable because forest residue and dead animal matter will always be replenished, and will always be replaced within a lifespan.
- It takes care of things that might have been left to rot in a landfill.
- They are carbon neutral, meaning that the plants take in the CO2 that was removed, creating balance and no extra carbon is released.
- They are in their early stages still, and not many biofuel power plants exist.
- If biofuel became more popular, then we would need land to grow willow etc, things that can be regrown quickly and harvested.
Hydroelectricity is a renewable source of energy that uses the GPE in water in mountains or lakes, or kinetic energy stires in rivers to turn the turbines.
- They are a good replacement to fossil fuels and produce no pollutant gases. It is the greenest ways to produce electricity.
- They are reliable, especially because GPE will always exist in areas of mountains etc.
- Water is a replenishable fuel - we just have to exploit its pressure, so nothing is being "used up"
- They are very expsensive to build.
- They require a dam to be built, which can be considered an eyesore.
- People may be forced out of an area which is required to be flooded.
- Flooding an area leads to loss of homes and agriculture.
Geothermal energy is the heat that comes from the sub-surface of the earth. It is contained in the rocks and fluids beneat the earth's crust.
How it works:
Hot water and steam from underground to drive turbines. Cold water is pumped beneath the surface of the earth, which causes warm water to rise, then it is turned into steam to drive turbines to produce electricity or heat houses.
- In volcanic areas or tectonic boundaries (countries), this can be used abundantly.
- It is cost-effective.
- It has no negative effects on the environment and it is clean.
- It cannot be used in the majority of countries that do not have their locations near tectonic plate boundaries, e.g. UK.
Tidal power is a form of hydropower that converts the energy obtained from moving tides into electricity.
- Reliable, as high and low tides come twice a day although their flow is variable.
- It is clean.
- It affects the marine life.
- It causes flooding as a barrage needs to be built.
- It can be expensive, but it isnt always so.
- It can change the wildlife.
Wind energy is created when the moving air in the atmosphere turns the turbines.
- It is green and has no environmental impacts.
- It is good for places like the UK, as we have a lot of wind in mountainous regions.
- Can be considered an eyesore, which causes visual pollution to the landscape
- They cause noise pollution.
- They are totally dependent on the wind, so if there is no wind, then there will be no electricity produced that day.
Solar power is power generated directly from the sunlight. Solar power can be used for heat energy or be converted into electricity.
- They can work well in cloudy and rainy conditions.
- It has the greatest potential to produce electricity when non-renewable resources run out.
- It is clean and green, and has no negative impact on the environment, as it exploits the process of sunlight.
- They can be neatly packed and placed on top of roofs.
- They can be considered an eyesore.
- In a country like the UK, where there is little sunlight in the winter, it may be hard to power a home.
- They are considerably expensive.