Motion Force and Energy

Motion Force and Energy

• Energy, work and power are aspects of motion, force and energy
• Energy is the ability to do work
• Energy is a scalar quantity, requiring a magnitude

Units and Symbols

• The symbol for energy is E
• The units for energy are joules (J), kilojoules (kJ), megajoules (MJ), and kilowatt hours (kW h)

Forms of Energy

• Energy can be transferred and stored
• Kinetic
• Gravitational potential
• Chemical
• Elastic (strain)
• Nuclear
• Internal
• Electrostatic
• Light
• Sound

Energy Transfer and Storage

• Energy transfers occur between stores during events and processes.
• Examples include:
• Mechanical work done by forces
• Electrical work done by electrical currents
• Heating
• Electromagnetic, sound and other waves

Kinetic Energy

• Kinetic energy is the energy an object has due to its motion.
• Ek = 1/2 mv²
  • Ek = kinetic energy
  • m = mass of object in kilograms (kg)
  • v = velocity of object in meters per second (m/s)

Gravitational Potential Energy

• Gravitational potential energy is the energy an object has due to its position in a gravitational field.
• ΔΕp = mgΔh
• ΔΕp = change in gravitational potential energy
• m = mass of object in kilograms (kg)
• g = gravitational field strength in N/kg
• Δh = height change in meters (m)
• (mg is the weight of the object)

Chemical Energy

• Chemical energy refers to the potential of a chemical substance to undergo a transformation through a chemical reaction or to transform other chemical substances.
• It is a store of energy.
• Energy is stored in batteries, fuels, and food.

Elastic (Strain) Energy

• Elastic (strain) energy is the energy stored by an object that has been stretched, squashed, or bent elastically, allowing it to return to its original dimensions upon force removal.
• Examples are clockwork toys and clocks, elastic bands and springs, even the branches of a tree

Nuclear Energy

• Nuclear energy is the energy stored inside the nucleus of atoms.
• Nuclear power stations are designed to release nuclear energy from uranium.

Electrostatic Energy

• Electrostatic energy is a store of energy due to the buildup of charge.
• Electric currents transfer energy from one place to another.
• Charge gets energy from the power supply, then carries it around the circuit.

Internal (Thermal) Energy

• Internal (thermal) energy describes energy stored in an object due to the movement of its molecules.
• Thermal (heat) energy radiates from a hot body.
• Energy travels from a hotter body to a colder body.

Light Energy

• Light energy radiates outwards around a hot object.
• Light is part of the electromagnetic spectrum.

Sound Energy

• Sound energy transfers to an object's surroundings.
• This is known as a sound wave.

Energy Conservation

• Energy cannot be created nor destroyed as it changes from one form to another or to another place.
• Total energy in an isolated system remains constant.
• Energy's most useful form is when converted from one to another.
• Processes waste energy, spreading it among objects and surroundings, and is eventually dissipated.
• The sum of energies at one point equals the sum of energies at another point.

Sankey Diagrams

• Sankey diagrams show energy transfers that take place in a process.
• The wider the line or arrow, the greater the amount of energy.

Work

• Mechanical or electrical work equals the energy transferred
• W = Fd = ΔΕ
  • W = work done
  • F = force in the direction of the movement
  • d = distance
  • ΔΕ = energy transferred
• Work is measured in Newton meters (Nm)

Examples of work

• shopping trolley
  • Pushing force does work
  • Transfers energy to the trolley
  • increases the EK of the trolley
• apple falling
  • Gravity pulls the apple downward
  • gravity does work
  • The apple's EK increases
• Bicycle Braking
  • Brakes create a backward force of friction
  • Friction slows the bicycle down
  • As friction does work the bicycle EK decreases
  • Energy is transferred to the brakes causing them to heat up

Energy Resources

• Useful energy may be obtained (or electrical power generated) from:
  • Chemical energy:
    • Fossil fuels
    • Biofuels
  • Water:
    • Stored in waves
    • Tides
    • Water behind hydroelectric dams
  • Geothermal resources
  • Nuclear fuel
  • Light from the sun (solar cells)
  • Infrared and electromagnetic waves from the sun:
    • Heating water (solar panels)
    • Wind energy

Renewable vs Non-Renewable Resources

• Non-renewable resources:
  • Used at a greater rate
  • Fossil fuels: oil, gas, coal
• Renewable resources:
  • Replenished faster than they are used

Electricity Generation

• Electricity generation is efficient when many different energy resources are used

Chemical Energy (Fossil Fuels)

• Fossil fuels: coal, oil, and natural gas
• Formed from remains of living organisms millions of years ago.

Fossil Fuels (Advantages)

• Reliable
• Large scale use
• Still widely available

Fossil Fuels (Disadvantages)

• Fuels are non-renewable
• Coal and oil release sulfur dioxide, which causes breathing problems
• Contribute to acid rain
• Fossil fuels release carbon dioxide, increasing the greenhouse effect, contributing to global warming
• The most carbon dioxide emissions come from burning coal (for a given amount of energy released)

Biofuels

• Biofuels: fast-growing trees and wheat

Biofuels (Advantages)

• Renewable
• Reliable

Biofuels (Disadvantages)

• Still pollute
• Currently small scale

Fossil Fuels and Biofuels

• Chemical energy is stored in fuels: coal, oil, gas, biomass, and biofuels.
• Fuels are burned to release energy in the form of heat (with sound and light as waste energy).
• Heat boils water and turns it to steam.
• The steam moves (kinetic energy, and sound and light as waste) and turns a turbine (kinetic energy, and wasted sound and heat).
• Turbines turn generators (kinetic energy, and wasted sound and heat), which generates electrical energy.

Kinetic Energy from Waves

• Kinetic energy from waves drives air up and down a chamber (kinetic energy, with wasted sound and heat).
• The chamber turns a turbine (kinetic energy, with wasted sound and heat).
• This turbine turns a generator (kinetic energy, with wasted sound and heat), generating electrical energy.

Wave Energy

• Wave energy is a renewable energy resource with no fuel costs
• It produces no harmful polluting gasses
• Wave energy power is difficult to scale in designs, not reliable and not widely available.

Water (Tidal Energy)

• A barrage is placed across a river outlet, which has a large tidal change.
• Water is held back behind the barrage, creating gravitational energy.
• Water subsequently flows through the barrage and turns a turbine (kinetic energy, with wasted sound and heat).
• The turbine then turns a generator (kinetic energy, with wasted sound and heat), which generates electrical energy.
• The process repeats in the other direction when the tide changes.

Tidal Barrages

• Tidal barrages are a renewable energy source and have no fuel costs
• Tidal barrages cause no harmful polluting gasses
• Tidal energy is reliable and can be switched on easily
• Tidal barrages destroy estuary habitats and are not widely available

Hydroelectric Dams

• Water gets held back behind a dam, and has gravitational energy.
• As the water falls, this energy changes into kinetic (with wasted sound and heat).
• Next, water turns a turbine (kinetic energy, with wasted sound and heat), which spins a generator (kinetic energy, with wasted sound and heat).
• Finally, the system generates electrical energy.

Hydroelectric Powerstations

• Water power in its various forms is a renewable energy source and there are no fuel costs.
• No harmful polluting gases are produced by hydroelectric powerstations
• Hydroelectric power stations are very reliable and can be easily switched on.
• Hydroelectricity damages flood farmland and push people from their homes.
• The rotting vegetation underwater releases methane, which is a greenhouse gas.
• Hydroelectricity is not widely available

Geothermal Resources

• Rocks under the surface of the Earth are hot and close to the surface.
• Cold water pumps down into the rocks, returning to the surface as steam.
• Steam moves (kinetic and some light and sound as waste).
• The steam turns the turbine (kinetic, and wasted sound and heat) which turns a generator (kinetic energy, wasted sound and heat).
• Electrical energy is then generated in the generator which is powered by a turbine.
• Alternatively, passive systems use the hot water to warm building in some areas.

Geothermal Energy

• Geothermal energy is a renewable resource without fuel costs
• No harmful polluting gasses are produced.
• Energy is reliable
• Most parts of the world do not have suitable areas to generate geothermal energy and is therefore small scale

Nuclear Fuel

• Nuclear fission: a heavy, large nucleus is split into smaller parts with neutrons.
• Large amounts of fast-moving particle energy (kinetic).
• These particles generate heat energy.
• Released neutrons then split other nuclei to release more neutrons and energy in a chain reaction.
• Nuclear reactors use control rods to absorb the neutrons and prevent energy released, but that's not always fool proof

Nuclear Fission

• Nuclear fuels, unlike fossil fuels, do not produce carbon dioxide or sulfur dioxide.
• Fossil fuels, nuclear fuels are non-renewable energy resources
• Accidents and earthquakes can lead to excess released radioactive material in the environment
• Nuclear radiation has hazardous health effects for thousands of years and must be stored safely.

Solar Cells

• Photovoltaic cells turn heat and light energy from the sun directly into electrical energy.
• This can then be stored in batteries or used directly.

Solar Energy (Advantages)

• Solar energy is a renewable resource without fuel costs
• Solar energy doesn't produce harmful polluting gasses
• Solar cells provide electricity in remote locations (roadside signs).

Solar Energy (Disadvantages)

• Solar cells are expensive and inefficient, making electricity expensive.
• Solar cells do not work at night
• Small Scale
• Storing solar electrical energy is a problem

Solar Panels

• Heat and light energy from the sun can heat water, which warms houses or offices.
• The Solar Collector with copper pipes are painted black and placed behind glass to conduct heat through the water.

Wind Energy (Advantages)

• An alternative to fossil fuels is plentiful
• Renewable
• Widely distributed
• Clean: produces no greenhouse gas emissions

Wind Energy (Disadvantages)

• Spoil visual environment
• Not currently widely available
• Can be noisy

The Sun

• Radiation from the Sun is the main source of energy for all our energy resources except geothermal, nuclear, and tidal.
• The energy released by the sun is through nuclear fusion.
• Nuclear fusion in hydrogen creates helium at increased pressures
• Nuclear fusion is being researched to produce increased electrical energy

Nuclear Fusion Power

• Nuclear fusion energy may offer prospects of almost inexhaustible energy.
• Engineering challenges include achieving higher heat from a fusion plasma to exceed injected plasma energy.
• Current research focuses on tokamak reactors and stellarators.
• Experiments by the European Union, USA, Russia, Japan, China, Brazil, Canada, and Korea

Efficiency

• Wasted energy is transferred, spreading out very thin
• Efficiency is the ratio of useful energy output to total energy input.
• Efficiency is the ratio of the useful power output to the total power input

Power

• Power is defined as work done or energy transferred per unit time.
• Also refers to how much can be completed or transferred in a measured time
• Power is proportional to work done and inversely proportional to time taken.
• Must be measured in seconds with 1 J/s = 1W
• Power is symbol P and the units are Watts (W), Kilowatts (KW), and Megawatts (MW)