Work, Energy, Thermal physics Flashcards
Types of energy 9
-> Energy is basically the ability to do some work
1. Kinetic (in all moving objects)
2. Nuclear (radioactive substances)
3. Chemical (stored in food, fuels, batteries)
4. Electric (in wires)
5. Gravitational potential (high-up objects)
6. Elastic potential (stretched or compressed objects)
7. Thermal energy
8. Light energy
9. Sound energy
Radiation energy/ Mechanical energy
Law of conservation of energy:
Energy cannot be created or destroyed, only transferred from one store to another.
Kinetic energy and GPE
E (J) = mass (kg)* gravitational acceleration (m/s^2)*vertical height (m)
1/2mass(kg)velocity^2 (m/s) 1/2mv^2
Two objects of different masses dropped from the same height (with no air resistance) will be travelling at the same speed when they hit the ground!
M can be cancelled out from both equations when using the two formulas!
Work
-> Energy transferred
Work is done on an object when:
- a force moves it a certain distance in the direction of the force
- energy is gained
W (J)= F (N) xd (m)
Whenever energy is being transferred, work is being done either as mechanical or electrical work.
Power
-> Power is a measure of how quickly work is done, or: the rate at which energy is transferred.
The unit of power is the watt (W). When we say the word ‘rate’, we mean how much is done per second, so 1 watt is the same as 1 joule transferred per second.
Brownian motion & kinetic theory
-> Random, jerky, and continuous motion of dust/pollen particles that are large enough to be seen. They are pushed around by the air particles.
Supports the Kinetic theory:
1. Particles are in continuous motion
2. Particles move faster in a hot substance
3. Particles in a gas are further apart in solids
4. Cold air sinks
5. Particles in solids have strong bonds
6. No bonds between gas particles
The slow, random motion of microscopic particles comes from collisions with fast-moving atoms and molecules that have considerably less momentum due to their much smaller mass.
Evaporation vs boilng
Evaporation happens when a liquid is exposed to the air: the particles escape intermolecular forces from the surface if they move fast enough. This process happens at the surface and any temperature below the boiling point.
Factors affecting evaporation:
- Surface area – more particles escape at same time
- Initial temperature – fast particles escape more easily
- Type of liquid – different intermolecular forces
- Movement of air – liquid particles get energy from moving air
Boiling happens everywhere in the liquid and the liquid needs to be at its boiling point.
Volume, pressure, and temperature
Gas pressure in a container is due to the force exerted on the walls of the container per unit area. Pressure increases as the force produced by the collisions of particles increases.
Increasing the temperature, increases the velocity of each particle. This increases the gas pressure as particles collide with the container with more force.
If the temperature of a gas is constant, decreasing the volume of the container increases frequency of collisions, so the pressure increases.
Thermal expansion
When substances are heated, their particles gain energy and move faster and further apart, so the distance between them increase, known as thermal expansion.
In solids, particles vibrate more but stay close together, so expansion is small. In liquids, particles move more freely, causing greater expansion. In gases, particles move the fastest and spread out the most, leading to the greatest expansion.
According to the kinetic theory, heating increases particle movement.
In solids, strong forces keep particles close, so expansion is small. In liquids, forces are weaker, allowing more movement. In gases, particles are far apart with almost no force, so they expand the most when heated.
Thermal expansion is used for:
- Mercury in thermometers
- Railway buckling
Thermal expansion can cause:
- Burst of metal pipes carrying hot water
- Wall collapse due to bulging
Conduction
-> a process that transfers energy from one part to another until the temperature of all the parts is the same (mainly in solids)
Lattice vibration: when part of the material is heated to a higher temperature, the atoms begin to vibrate even more rapidly around their positions. This increase in vibration affects other, nearby atoms – it causes them to vibrate more so the temperature in that area also increases. The process gradually causes increased vibration and increased temperature across all the material.
Conductions in metals: It happens faster due to their giant metallic structure: they have a sea of delocalized electrons (can move freely and quickly from one end to another, making metals a good thermal conductor).
When part of the metal is heated, the electrons in this area quickly spread out along the metal. As they travel, they collide with the atoms and cause increased vibration, raising the temperature.
Materials are then classed by their thermal conductivity – the higher the thermal conductivity, the quicker the energy is transferred through the material. Materials with very low thermal conductivity are thermal insulators.
Convection
-> A process that transfers energy within a fluid due to density changes.
When a fluid is heated, they expand, meaning that their density decreases. As the liquid is heated and becomes less dense than the liquid around it, it will begin to float upwards towards the surface. The warmer liquid rises upwards. At the surface, the liquid will begin to cool and become denser. This will cause it to sink back downwards.
These processes cause a circulation of the fluid called a convection current. Fluid is constantly rising upwards, spreading across the top and falling back down again.
Radiation
-> A hot object emits infrared radiation. When the object emits this radiation, it cools down – the particles inside it slow slightly and so the temperature falls as the internal energy decreases. The hotter an object is, the more radiation it will emit each second.
Objects can also absorb radiation, causing them to warm up. This radiation can be infrared or visible light. As the radiation is absorbed the temperature of the object increases.
Objects at room temperature are emitting infrared radiation but they are also absorbing the same amount of radiation. This means that their temperature stays the same because there is no overall change in their internal energy.
What affects absorbing and emitting radiation:
1. Colour
- Silvered surfaces are poor absorbers and poor emitters
- Black surfaces are good absorbers and good emitters
- Texture
- Shiny surface are poor absorbers and poor emitters
- Dull surfaces are good absorbers and good emitters
Why does all energy come from the sun? Disagree? Explain.
Most energy comes from the sun, including energy in coal (or fossil fuel), wind and waves.
NON-RENEWABLE SOURCES: Prehistoric plants store the sun’s energy in their leaves, and when they die the energy form coal seams. When we burn coal, we are actually releasing the chemical energy stored there, but the source is still the sun.
RENEWABLE SOURCES: Waves occur because of winds, and there are winds because the sun warms up the Earth’s atmosphere: the warm air rises, and other air moves to replace it.
EXCEPTIONS: Energy such as nuclear and geothermal (heat inside the Earth’s crust) do not come from the sun.
Fossil fuels
FOSSIL FUEL POWER PLANT (2-3)
FOSSIL FUELS -> Includes coal, oil and natural gas. Got the name because they are organic remains of prehistorical plants and animals. Non-renewable energy.
HOW DOES IT WORK?
1. Coal is crushed and burnt (oil and gas burnt directly) to produce heat energy
2. Water in boiler is boiled and turns into superheated steam (high pressure)
3. Steam turns the turbines and condenses back into the boiler using a condenser
4. The kinetic energy in turbine turns the coiled wire in the generator which produces electricity
5. The electricity can then be distributed and used
ADVANTAGES:
- Large amount of electricity can be generated in one place using coal cheaply
- Transporting oil and gas to power stations is easy
- Gas-fired power is efficient
- Can be built almost anywhere, as long as you can supply fuel
DISADVANTAGES:
- Pollution (greenhouse gases such as CO2, especially coal)
- Contributes to acid rain (produce sulfur dioxide)
- Mining coal and be difficult and dangerous. Strip mining destroys landscape
- Covers a large area of countryside next to the power station with piles of coal (need reserves for changing demand of power)
Nuclear power plants
Nuclear energy -> generates heat from nuclear fission: neutrons smash into the nucleus of the uranium atoms, which split in half and release energy in the form of heat. Non-renewable energy.
HOW DOES IT WORK?
1. Heat is generated through nuclear fission
2. Water in boiler is boiled and turns into superheated steam (high pressure)
3. Steam turns the turbines and condenses back into the boiler using a condenser
4. The kinetic energy in turbine turns the coiled wire in the generator which produces electricity
5. The electricity can then be distributed and used
Advantages:
- Cost same as coal; not expensive to make
- No carbon dioxide produced; doesn’t contribute to greenhouse effect
- Produce large amounts of energy from small amounts of fuel
- Small amounts of waster
Disadvantages:
- Produced waste is radioactive, dangerous and hard to dispose -> must be sealed up and buried for thousands of years
- Lots of money spent on safety – if an accident happen the consequence are severe, causing deaths and disease and contaminating the area for a long time
- Because of safety precautions, they take long time and are expensive to build and decommission.
Pumped storage
-> not way of generating electrical power but a way of storing energy to be released when needed. Neither renewable nor non-renewable energy because not an energy resource.
HOW DOES IT WORK?
1. Water is pumped to the top reservoir at non-peak hours when the demand for power is low
2. When there is a sudden demand for power (at peak hours), the headgates are opened
3. Water rushes down and drives the turbines, which drives the powerful generators
4. Water is then collected at the bottom reservoir, ready to be pumped back up at non-peak hours.
Advantages:
- Fast respond time to sudden demand for power
- Little effect on landscape
- No pollution or waste products
Disadvantages:
- Expensive to build
- Once it’s used, you can’t use it again until you’ve pumped the water back up (good planning can get around this problem).
Hydroelectric systems
-> One of the three (hydroelectric, tidal, and wave) methods of generating electricity. Renewable energy.
How does it work?
1. A dam wall is built on a river
2. By holding the water behind the wall, a large height difference is achieved between water upstream and downstream, the water gaining gravitational potential energy
3. Water rushes down tunnels in the dam at high pressure (gains kinetic energy) which drives turbines that generate electricity
Advantages:
- Once the dam is built, the energy is virtually free
- No waste or pollution produced
- Electricity can be generated constantly
- Water can be stored above the dam for peaks in demand
Disadvantages:
- Building a large dam will flood a very large area upstream, causing problems for animals that used to live there
- The dams are very expensive to build; dams can also be used for flood control, so building costs can be shared
- Water quality and quantity downstream can be affected, which can have an impact on plant life
PHOTOVOLTAIC CELLS
-> a nonmechanical device that converts sunlight directly into electricity; also known as ‘solar cells.’ Renewable energy.
HOW DOES IT WORK?
1. Solar cells produce electricity directly from electromagnetic waves in sunlight
2. This is transmitted through power lines to homes across the world
Advantages:
- Does not produce greenhouse gas or waste products
- Solar energy is free
- In sunny countries, solar power can be used where there is no easy way to get electricity to a remote place
- Good for low power uses, such as solar powered garden lights
Disadvantages:
- Not very efficient
- Expensive to build solar power stations
- Output depends on the amount of sunlight (Doesn’t work at night)
Wind generators
-> uses wind turbines. Renewable energy.
HOW DOES IT WORK?
1. The sun heats up the Earth’s atmosphere, warming up air
2. Warm air rises, and cooler air moves in to replace it, creating wind
3. The wind turns the blades of a wind turbine, which turns the generator
4. The kinetic energy from the moving wind is turned into electrical energy
5. Many wind turbines are often grouped together in large areas called “wind farms” to generate more electricity
ADVANTAGES:
- Wind is free
- No greenhouse gas or waste products produced
- Land beneath can still be used for farming
DISADVATAGES:
- Wind is not predictable or reliable
- Land suitable for wind farms (near coast) are usually expensive
- Can make constant noise (though new designs are much quieter)
- Can affect television reception
Biomass
-> organic material that comes from plants and animals. Renewable energy.
HOW DOES IT WORK?
1. Biomass is burnt to produce heat energy
2. Water in boiler is boiled and turns into superheated steam (high pressure)
3. Steam turns the turbines and condenses back into the boiler using a condenser
4. The kinetic energy in turbine turns the coiled wire in the generator which produces electricity
5. The electricity can then be distributed and used
ADVANTAGES:
- Fuel tends to be cheap
- Using waste materials
- Lowering demand of fossil fuels
DISADVANTAGES:
- Collecting fuel in sufficient quantities can be difficult
- We still burn the biofuel, so greenhouse gases are produced
- Some waste materials are not available all year round
