P1D2 - energy, work and power Flashcards
What is energy?
Scalar quantaty that represents the ability to do work or tranfser heat. Measured in Joules.
Name 7 different types of different stores of energy
- Kinetic store of energy - stored in moving objects. E.g. ball being kicked
- Chemical store of energy - stored in bonds of chemical compounds and released in chemical reactions. E.g. food, batteries
- Nuclear store of energy - stored in every atom and released during nuclear fission/fusion. E.g. uranium is a nuclear energy store used to generate electricity in nuclear power stations
- Thermal/internal store of energy - the energy stored in a system by the movement of its particles. E.g. the energy needed to change the state of a substance
- Electrostatic store of energy - stored when electrically repellent charges are moved closer together. E.g. thunderstorm
- Elastic potential/store of energy - stored in stretched/compressed objects. E.g. a bow that has been stretched to fire an arrow
- Gravitational potential store of energy - stored in any object that is lifted upwards through a gravitational field. E.g. climbing a ladder is hard work because you store GPE as you climb
Give 3 examples of energy transfers
When work is done, an energy transfer occurs from one store to another.
1. Car driving uphill: chemical energy (petrol) -> kinetic energy (moving) -> GPE (going up the hill)
2. Current generator connected to a bulb: chemical energy (stored in muscles which turns the generator)-> electrical energy -> light + heat
3. Electric motor lifting a load: electrical energy -> kinetic energy (motor) -> GPE
Explain the energy transfer from wind turbine to light bulb
Kinetic energy of wind -> kinetic energy of wind turbine -> electrical work -> internal energy (heat+ light). This energy is transferred to the surroundings via light waves where it is stored as heat.
What is the conservation of energy?
Energy cannot be created or destroyed, only transferred from one store to another.
Formula for kinetic energy
1/2mv^2
Formula for GPE
mg x change in height (m)
Explain a ball falling and being thrown upwards in terms of kinetic energy and GPE
Ball falling - GPE (from the height at which is is dropped) -> kinetic energy (as it loses height but increases speed)
Ball being thrown upwards: KE (initial velocity) -> GPE (at max height reached, GPE is equal to KE at the start) -> KE (as ball falls back down)
Why does mass not affect the speed of a falling object?
1/2mv^2 = mg x change in height (if there is no friction)
the mass cancels out.
If 2 objects of different masses are dropped from the same height, if there i no air resistance they will hit the ground with the same speed.
What is work + formula
Work done = energy transferred
For work to be done, something must be moving in the direction of the force being applied.
Examples: person walking up stairs, lifting weight over your head
Work done (J) = force (N) x distance moved in the direction of the force (m)
A toy electric car has a total store of 20 kJ in its batteries. When it moves forwards, friction and air resistance produces a force of 50 N on the car. How far could the car travel against this force?
400m
d=w/f
d=20000/50
d=400
Name 7 types of power plants
- Fossil fuels
- Nuclear
- Pumped storage
- Hydroelectric systems
- Solar panel
- Wind generators
- Biomass
- Water (waves, tidal)
- Geothermal
Explain fossil fuels as an energy source
The 3 types of fossil fuels are : coal, oil and natural gas. Burning these fossil fuels results in the transfer from chemical to heat energy. If we wish ti generate electricity, the heat from the fuel boils water to produce steam. High pressure steam rushes down pips to turbines. These turn like windmills and make a generator spin at high speed, which produces electricity
+ cheap to build power plant; reliable as they produce energy at all times; high power output
- releases CO2 which contributes to global warming; non-renewable - since they took millions of years to form, it is not possible to produce more once they run out
Explain nuclear fission in power plants
In nuclear fission, energy is released when heavy nuclei with very large nucleon numbers (which are often unstable) break apart, either on their own or by firing neutrons at it.
+ no greenhouse gases emitted - good for environment; high energy density - very efficient as each kilogram produces enormous amounts of energy.
- non-renewable (uranium is finite); produces radioactive waste - not eco friendly & difficult to dispose; expensive and time-consuming to build
How does pumped storage work + what is it?
It is a power plant which is used to store energy when demand for electricity is low. This is done using 2 water reservoirs at different elevations. When there’s excess power on the grid, it is used to pump water from the lower to the upper reservoir using reversible turbines. When demand is high, water is released downhill, turning the turbines in the other direction and generating electricity.
+ 90% efficient in storing energy for later use; long-lasting; generates renewable electricity without direct greenhouse gas emission
- building infrastructure can be expensive; some energy is lost during pumping; needs specific geography; may disrupt ecosystems
What are hydroelectric systems + how do they work?
A dam is built over a river. By holding the water behind a wall, a large height difference is achieved between water upstream and downstream, which means that the water behind the dam stores GPE. This is converted into kinetic energy when the water is released downstream through pipes with turbine blades, which when turned generate electricity.
+ renewable; no greenhouse gas emission; electricity can be produced 24/7
- habitat and homes destruction due to initial flooding when building dam;
What are solar panels + how do they work?
Solar panels are made of photovoltaic cells. These are made out of a semi-conductor, which allows photons with sufficient energy levels to pass through it. When enough solar energy is absorbed, electrons are dislodged from the material’s atoms. They travel to the front of the cell, which causes an imbalance of charges between the front and back of the cell. This creates a voltage potential similar to a battery. If connected to an external load in an electrical circuit, electricity will flow through it.
+ renewable energy; free energy production; low maintenance; long life span
- weather dependent; high initial cost; difficult + expensive to store excess energy
How do wind generators work?
Wind turns the blades of the wind turbine. The KE is then converted into electrical energy using a generator
+ renewable, no greenhouse gas emission; easy & cheap to produce
- sound & visual pollution; dependent on weather; lots of turbines needed to produce significant amount of energy
How is biomass used to generate electricity?
Biomass such as wood and animal waste is burned in a combustion chamber, which releases heat hat boils the water in a boiler, turning it into steam. This turns the turbine which drives the alternator to produce an electric current.
+ renewable; low co2 production; reduction of waste
- air pollution with other harmful gases; need a lot of space/land; high costs from transportation, storing, etc
Explain 2 ways to generate electricity from water
- Tide - similar to hydroelectric systems; seawater is trapped behind dam. During high tide, water is forced to flow through turbines, which generates electricity
+ renewable; no greenhouse gases; tides are predictable
- can damage ecosystems; few places have sufficiently large tides - Wave - uses movement of waves up and down to drive turbines, which produces electricity.
+ renewable; no greenhouse gas
- not reliable due to new technology; lower power output
Name 3 energy resources which are not originally from the Sun
- Nuclear power
- Tidal power
- Geothermal power
How does geothermal energy source work?
Cold water is fed through pipes underground and returns as steam due to volcanic activity. The steam drives turbines to generate electricity.
+ renewable; reliable output; no greenhouse gases
- few volcanic countries; low power output
State the 2 formulas for efficiency
- useful energy output/energy inpyt x 100 = efficiency
- useful power output/power input x 100 = efficiency
Give 2 examples of where energy is wasted
- Ball bouncing - not all is transferred between GPE and KE. Some is lost/transferred to internal store of energy or sound energy
- Light bulb - not only light energy but also internal store of energy (heat)
What is power?
The measure of how quickly work is done or the rate at which energy is transferred.
Unit: Watt (W)
energy transferred (or work done, Joules)/ time taken (s) = power (W)
If an object has both GPE and KE, add the 2 together to get the energy transferred and then divide by the time.
The KE of a helicopter is 620kJ and its GPE is 550kJ. It took it 22 seconds to get this energy. Calculate its power.
620000+550000/22 = 53.2 W
Explain 2 experiments on how to find your power
- Walking up the stairs - measure the height of one stair, multiply it by total number of stairs. Start the timer and record how long it takes to walk up a certain number of steps. Calculate your power by doing your mass x 9.8 x height climbed/time taken.
- Dumbbell - place your arm on the table vertically so that your elbow is touching the table. Record distance from table to middle of your palm and multiply that by 10. Take a dumbbell, and lift your hand 10 times, from lying on the table to vertically standing (elbow still touching table). Record how long it took to do that. Calculate your power by doing mass of dumbbell (kg) x 9.8 x height lifted/time taken
Why is walking on a flat surface at a constant speed not considered work being done?
There is no energy transfer, and no movement in the direction of the exerted force. The force you exert vertically to counter gravity does not cause displacement vertically. Since you are walking at a constant sped, there is no net force so no energy transfer.
