P2: Work

Work

Work is the measure of energy transfer when a force moves an object for a distance. Therefore, work done is equivalent to energy transferred

The formula for work is W=Fd OR Work (Joules) = Force (Newtons) x Distance (meters)

  • Work is done when a force moves an object in the same direction it applies
  • For example, pushing a box is doing work
  • If we push the box with a force of 10N and a distance of 10m, the amount of work done would be 100J


Energy
  • Objects may have kinetic energy or potential energy based on their position or movement. This energy cannot be destroyed or created, but instead can be transferred and stored
  • Energy is transferred and transformed through many events


Equations

  • Kinetic energy (Joules) = 1/2mv2 OR 1/2 x Mass (kg) x Velocity2 (m2/s2)
  • Gravitational potential energy (Joules) = mgh OR Mass (kg) x Gravity (N/kg) x Height (m)


Types of Energy

  • Kinetic Energy: Energy from an object's motion (eg. a moving car)
  • Gravitational Potential Energy: Stored energy from the height of the object because of gravity (eg. a ball held on top of the ground)
  • Chemical Potential Energy: Energy from stored in chemical bonds (eg. the energy stored in fossil fuels)
  • Elastic Potential Energy: Stored energy from stretching an elastic object with a force (eg. a stretched spring or rubber band)
  • Nuclear Energy: Energy within an atom's nucleus (eg. used in reactions in nuclear plants, fusing or forcing apart atoms)
  • Thermal Energy: Energy from the movement within the object (can be transferred in the form of heat). An example of thermal energy is boiling a kettle, or the warmth from the sun.
  • Light Energy: Kinetic energy creating visible light (eg. seen in sunlight and the light from lightbulbs)
  • Sound Energy: Energy from the vibration of the object making a sound (striking a bell, instruments playing)
  • Electrical Energy: Energy from the movement charged particles (used in electronic devices)


Conservation of Energy

The rule that energy cannot be created or destroyed, but can only be transferred from an object to another. Therefore, the total amount of energy present within the objects affected will not change.



Efficiency
  • When transferring energy, some of it is often wasted into other forms of energy such as heat, light, or sound
  • Efficiency is the ratio of useful energy output transferred to the total energy input
  • For example, if 75% of a machine's energy works the machine and 25% is wasted as heat energy, the efficiency of the machine would be 75% as that is the percentage of useful energy output
  • Formula for efficiency
    • Efficiency (%) = Useful Energy Output (Joules) ÷ Total energy input (Joules)
    • OR
    • Efficiency (%) = Useful Power Output (Watts) ÷ Total Power input (Watts)


Power
  • Power is the rate of energy transfer, which is calculated by the following equation
  • The formula for power is P = W/t OR Power (Watts)= Work (Joules) / Time (Seconds)


Energy Resources

Renewable and non-renewable sources of energy

  • Renewable sources: Sustainable sources of energy with infinite resources
  • Non-renewable sources: Sources of energy with finite and limited amounts of resources


Examples of sources of energy

  • Chemical energy stored in fuel:
    • Fuels are burnt, and the stored energy is released
    • The chemical energy transforms into heat energy and turns water into steam to turn turbines, generating electricity
    • Nonrenewable type of energy, pollutes environment and releases greenhouses gases
    • Low costs
    • Reliable
    • Can generate a lot of energy
  • Water energy:
    • Kinetic energy from the flowing water is used to drive electricity generators and turn turbines to generate electricity
    • Kinetic energy comes from tides and waves
    • Hydroelectric dams are built, and sometimes uses the gravitational potential energy from water high above the ground that turns into kinetic energy when falling into the tubes of the dams to turn the turbines
    • Renewable type of energy, but may disturb ecosystem
    • Can produce large amounts of energy
    • Can cause flooding, but does not release greenhouse gases
    • Energy from hydroelectric dams are reliable, but energy from tides are not
    • Expensive to build, but not expensive when working
  • Geothermal resources:
    • Steam is made from the heat from the earth, which spins the turbines and generates electricity
    • Renewable source of energy but could release harmful gases underground
    • Reliable
    • Does not provide large amounts of energy
    • It is worth the cost if the technology is placed in the correct locations (which are not common)
  • Nuclear fission:
    • An atom is split into two more atoms and release heat energy
    • The heat energy which boils water into steam
    • The steam turns a turbine to generate electricity
    • Non-renewable source of energy
    • Can produce large amounts of energy and is reliable
    • Does not emit greenhouse gases, but leaves radioactive waste that takes a long time to decay
    • Technology is expensive to run and make
  • Heat and light from the Sun (solar cells and panels):
    • Heat energy from the sun could make water warm, and be used for water heaters
    • Solar cells can transfer light energy from the sun to electricity
    • No pollution or greenhouse gas emission
    • Cannot produce large amounts of energy
    • Renewable source of energy
    • Not very cost effective unless government funds solar technology
  • Wind energy:
    • Wind energy can turn turbines to generate electricity
    • No greenhouses gases emitted and pollution
    • Wind turbines are very noisy
    • Turbines are expensive to install, but running the turbines are cheap
    • Not reliable


Energy source
  • Almost all energy resources come from the Sun
  • The heat from the Sun heats the atmosphere and creates wind (which creates waves)
  • Rain is water evaporated from the sun which fills up bodies of water
  • Biofuels and fossil fuels come from plants, which grow with photosynthesis and energy from the sun


However, there are some energy resources that do not come from the sun. This includes...

  • Geothermal Energy that comes from the heat from the Earth's core
  • Nuclear Energy that comes from elements on the Earth's crust
  • Tidal Energy: Mostly comes from the Moon's gravitational pull


The energy from the Sun comes from the process of nuclear fusion at its core. The nuclei (plural of nucleus) of hydrogen atoms fuse and form helium atoms



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