1 - Energy

What is a system?

What is a system?

An object or a group of objects

What happens to they way energy is stored when a system changes?

There are changes in the way energy is stored when a system changes.

What are the energy transfers when an object is projected upwards?

When an object is thrown up / dropped, energy is transferred from kinetic to GPE and back

What are the energy transfers when a moving object hits an obstacle?

The moving object will have KE, which is transferred to KE of obstacle (as it is hit and falls) and thermal of surroundings + sound waves

What are the energy transfers when an object accelerates by a constant force?

The accelerated objects KE increases, as energy is transferred from the objects chemical, thermal or electrical.

What are the energy transfers when a vehicle slows down?

The KE decreases and thermal energy of surroundings + brakes increase - some is also transferred to sound waves

What are the energy transfers when bringing water to a boil in an electric kettle?

Electrical current transfers energy to thermal of water, which increase KE of particles in water.

How can energy be transferred by heating?

Hotter objects transfer energy to cooler ones

How can energy be transferred by work done by forces?

Mechanically - a force acting on it (eg pushing, pulling, stretch, squash)

How can energy be transferred by work done when a current flows?

Electrically - changes due to a current (moving charges) flowing through a circuit

What is the energy associated with a moving object?

Kinetic energy

What is the energy associated with a stretched spring?

EPE - Elastic Potential Energy

What is the energy associated with an object raised above ground level?

GPE - Gravitational Potential Energy

What is kinetic energy?

The energy an object has because it is moving

What is the equation for kinetic energy?

1/2 x mass x speed squared

What are the units for all energy?

Joules - J

What are the units for mass?

Kilograms - Kg

What are the units for speed?

metres per second

What is elastic potential energy?

energy stored in a springy object when you stretch or compress it

What is the formula for EPE in a stretched spring?

1/2 x spring constant x extension squared

What are the units for spring constant?

Newtons per metre

What are the units for extension?

metres (m)

What is Hookes Law?

F = ke (k = spring constant) - The force needed to stretch a spring varies with its extensions

What is the limit of proportionality in a spring?

The max amt of stretching or compressing that a spring can undergo while still obeying Hooke's Law

What is Gravitational Potential Energy (GPE)?

the energy stored in an object because of its position (above the ground)

What is the equation for the GPE gained by an object raised above ground level?

mass x gravitational field strength x height (mgh)

What are the units for gravitational field strength?

Newtons per Kilogram

What is the gravitational field strength on earth?

9.8 or 10 N per Kg (they say it in the exam)

What are the units for height?

Metres (m)

What is the specific heat capacity?

The specific heat capacity of a substance is the amount of energy required to raise the temperature of one kilogram of the substance by one degree Celsius.

What is the equation for the change in thermal energy using specific heat capacity?

change in thermal energy = mass x specific heat capacity x temperature change

What is the change in thermal energy measured in?

Joules (J)

What is mass measured in?

Kg

What is specific heat capacity measured in?

Joules per kilogram per degree Celsius = J/Kg'C

What is temperature change measured in?

Degrees Celsius - C

What is power?

Power is defined as the rate at which energy is transferred or the rate at which work is done.

What is the equation for power?

Energy transferred over time

What are the units for power?

Watts

What are the units for time?

Seconds

What is an energy transfer of 1 joule per second equal to?

An energy transfer of 1 joule per second is equal to a power of 1 watt.

What is the conservation of energy?

Energy cannot be created or destroyed.

What are the only 3 things that can happen to energy?

Energy can be transferred usefully, stored or dissipated

What is the total energy in a closed system?

There is no net change to the total energy.

What happens to energy in all systems?

In all system changes energy is dissipated

What is dissipated energy?

Energy that is spread out in the surroundings so that it is stored in less useful ways - this energy is wasted

What are some ways of reducing unwanted energy transfers?

Through lubrication, using wires with less electrical resistance, streamlining objects, tightening loose parts and thermal insulation

How does lubrication help reduce unwanted energy transfers and increase efficiency?

Friction between the moving parts causes heating, so lubrication will reduce the friction.

How does using wires with less electrical resistance help reduce unwanted energy transfers?

The resistance of a wire causes the wire to get hot when a current passes through it, so less thermal energy will be wasted.

How does streamlining objects help reduce unwanted energy transfers?

Air resistance causes a force on a moving object that opposes its motion - energy transferred from object to surroundings is wasted - air resistance is less on streamlined objects

How does tightening loose parts help reduce unwanted energy transfers?

Sound created by machinery causes energy transfer to the surroundings - tightening loose parts will reduce vibration.

What is the relationship between thermal conductivity and the rate of energy transfer by conduction?

The higher the thermal conductivity of a material the higher the rate of energy transfer by conduction across the material.

How is the rate of cooling of a building affected by the thickness and thermal conductivity of its walls?

Thicker walls and materials with low thermal conductivity keep heat inside the building longer, resulting in a slower rate of cooling.

What is the equation for efficiency, using power?

useful power output over total power input

What is the equation for efficiency, using energy?

useful output energy transfer over total input energy transfer

What are the main renewable energy resources available for use on earth?

Nuclear, biofuel, wind, hydroelectricity, geothermal, the tides, the sun and water waves

What are the main non renewable energy sources available for use on earth?

Fossil fuels (coal, oil and gas) and nuclear energy

What is a renewable energy source?

A renewable energy resource is one that is being (or can be) replenished as it is used.

What are the uses of energy resources?

The uses of energy resources include: transport, electricity generation and heating.

How do fossil fuels work?

They are long dead animals or plants, which are extracted underground or from a seabed - the burning fuel heats water in a boiler, which produces steam, which turns a turbine which turns a generator and generates electricity

How does nuclear fuel work?

Nuclear fuel (uranium) takes energy from atoms and does nuclear fission, which releases energy from nucleus - the energy creates steam that drive turbine - drive generator - electricity.

How does biofuel work?

Its any fuel taken from organisms dead or alive (eg animal waste - they can be used instead of fossil fuels for transport and electricity generators - eg vegetable oils, ethanol, straw, nutshells, methane

How does wind energy work?

It is an electricity generator at the top of a tower - the force of the wind drives the blades around, which turns a generator which generates electricity

How does hydroelectric power work?

Hydroelectricity can be generated when rainwater collects in a reservoir and flows downhill, driving turbines that drive generators that generate electricity at bottom of hill

How does geothermal energy work?

Energy released by radioactive substances in the earth heats the surrounding rocks, which releases energy. This energy can heat the surface, or heats water pumped down to it, which creates stem to generate electricity or be pimped through buildings in pipes for direct heating.

How does tidal power work?

Traps water from a high tide behind a barrages which is then released into the sea through turbines, which drive generators

How does solar energy work?

Suns energy can be used to generate electricity using solar cells, or heat water directly in solar heating panels

How does wave power work?

A floating wave generator uses the waves to make it move up and down - this motion turns a generator, which generates electricity which is transferred to the grid by a cable between generator and shoreline

Which energy resources can be used for transport?

Biofuels, Fossil fuels, solar power, waves and wind power

Which energy resources can be used for heating?

Biofuels, Fossil fuels, Geothermal and Solar energy

Which energy resources can be used for electricity?

All of them

How is wind power unreliable?

Because when there is little or no winds, electricity cannot be generated

How is wave power unreliable?

They need to withstand storms, so they don't produce a constant supply of electricity, and when there are little waves, enough electricity can't be generated

How is hydroelectricity unreliable?

Droughts can happen, which dry reservoirs up

How is solar power unreliable?

They can be unreliable in areas where there is little sunlight or cloudy weather covering the sun, or at night as plenty of sunshine is needed to generate enough power to be useful

How is tidal power unreliable?

The height of tide varies both on a monthly and yearly cycle

What are the environmental impacts of wave power?

Lost of cables are needed along the coast to connect wave generators to the grid - this can spoil the coastline + tidal flow patterns can change, affecting marine life + birds

What are 3 environmental impacts of fossil fuels?

They release greenhouse gases and sulfur dioxide etc

How do fossil fuels releasing greenhouse gasses affect the environment?

This increases greenhouse gas levels in the atmosphere, which can cause more global warming and climate change

How does fossil fuels releasing sulfur dioxide affect the environment?

This gas causes acid rain, which can erode buildings and harm trees and the environment

How does tidal power affect the environment?

They affect river estuaries and habitats of creatures and plants there

How does hydroelectric power affect the environment?

They need large reservoirs of water, which can affect early plant and animal life + habitats are often flooded to create dams

What are the patterns of energy usage during the day?

There is a high usage, peaking in the morning and evening, when people are waking up, getting ready and retuning home, or at lunch and evening (cooking, tv etc)

What is the pattern of energy usage at night?

Energy demand decrease as people sleep + businesses shut down etc

What are the patterns of energy demand throughout the seasons?

Energy demand is more in the winter, as more ppl use heating, but it might spike in summer as more people use air conditioning + there is variance in holiday seasons, and agricultural seasons