Energy, Work and Power

Energy: Potential and Kinetic

• Energy is defined as the capacity of a body to do work.
• It is a scalar quantity.
• SI unit is Joules, J.
• A body can possess energy in various forms including, but not limited to:
  • Gravitational Potential Energy
  • Kinetic Energy
  • Chemical Energy
  • Elastic (Strain) Energy
  • Nuclear Energy
  • Internal Energy

Gravitational Potential Energy

• It is the energy possessed by an object due to its position and configuration
• 
  • • where PE is the Potential Energy in J
  • m is the mass of the object in kg
  • g is the acceleration due to gravity,  on the surface of the Earth
  • h is the height above the ground
• When an object is raised or lowered, it gains or loses gravitational potential energy.
• This change is given by the following equation:
  • 
  • where is the change in height of the object
• Note how it’s only the change in height that affects the gravitational potential energy, not horizontal movement

Kinetic Energy

• An object in motion possesses Kinetic energy that depends on its mass and speed.
• 
  • where KE is the Kinetic Energy in J
  • m is the mass of the object in kg
  • v is the speed of the object in m/s
• Note that the Kinetic energy depends a lot more on the speed of the object rather than the mass of the object.

Energy: Other forms

Chemical Energy

• Any energy that is contained and can be released by chemical reactions is known as Chemical energy.
• Examples –
  • Batteries
  • Fossil Fuels
  • Muscles in our bodies

Elastic (Strain) Energy

• Whenever a body is compressed or extended, it is said to contain elastic energy.

Example: extension of a spring

• In the subunit Forces topic Hooke’s Law, we learned about the Force versus Extension graph for a spring.
• The area under the force-extension graph is the elastic energy contained by the spring.
• 
  • where EE is the elastic energy in J
  • F is the force exerted to extend the spring in N
  • x is the extension in m

Nuclear energy

• When a highly energetic neutron collides with a Uranium nucleus, it splits into daughter nuclei.
• Energy is released as part of this process called the Nuclear Fission Reaction.
• The energy released is called Nuclear Energy.

• This reaction takes place in a nuclear reactor.
• An explosion of an atomic bomb also releases nuclear energy.
• the reaction is controlled in Nuclear Reactors, while in atomic bombs the reaction is uncontrolled.
• Contrastingly, Nuclear Energy is also released by the process of a Nuclear Fusion Reaction.
• The most well-known Fusion reaction takes place at the core of the sun.
• In this reaction, Hydrogen atoms combine to form a helium nucleus release a tremendous amount of energy.
• Unfortunately due to the strong forces of repulsion between the protons of the nucleus, a tremendous amount of energy is required to get the reaction started.
• Thus, replicating the Nuclear Fusion reaction is extremely difficult to perform artificially.

Internal Energy (Heat)

• In a substance, atoms rotate and vibrate with some energy called internal kinetic energy.
• Internal potential energy depends on the separation between atoms in a substance.
• Internal energy is the sum of these Internal kinetic and Internal potential energies.
• With increase in temperature both internal kinetic energy and potential energy increase.
• Therefore, internal energy increases with an increase in temperature.

Law of Conservation of Energy

• Energy can neither be created nor be destroyed, but it can be converted from one form to another.
• The following are a number of examples that showcase the transfer of energy as a ball falls off a hill.

Energy Resources and Efficiency

• In order to obtain useful energy such as Electrical Energy, it must be converted from some form it already exists in into Electrical energy.
• Example –
  • Chemical Energy (Fossil Fuels)
  • Potential and Kinetic Energy in Water (Tides, Hydroelectric Dams)
  • Heat Energy in Natural Gasses (Geothermal)
  • Nuclear Energy (Fission)
  • Heat and Light Energy (Sun)
  • Kinetic Energy in the Wind
• Note how the Sun is the original source of nearly all these forms of Energies except for Geothermal, Nuclear, and Tidal.

Chemical energy

• Chemical energy is stored in fuels such as Diesel, Petrol, and Coal
• These fossil fuels are burned in order to heat water.
• The steam is pushed through a turbine that rotates to produce electricity.

Potential and Kinetic Energy in Water (Waves, Tides, Hydroelectric Dams)

• The Kinetic energy from water waves can be used to push turbines in order to generate electricity.
• In case of Tidal and Hydroelectric Dams, the water is collected behind a barrier that allows it to gain Gravitational Potential energy.
• It is then slowly released and the Potential energy transforms into Kinetic energy as the water is then rushed through a turbine to generate electricity.

Heat Energy in Natural Gasses (Geothermal)

• Natural gasses are trapped in high pressure areas at high temperatures under the surface of the Earth.
• The heat from these gasses can be used to heat water, and similar to fossil fuels, the steam runs through a turbine to spin it and generate electricity.

Nuclear Energy in Radioactive Materials (Fission)

• The energy released by a Nuclear Fission Reaction can be used to boil water.
• The steam is then used to rotate a turbine to generate electricity.

Heat and Light Energy (Sun)

• Heat from the Sun can be converted to electricity by Solar Thermal Panels.
• Light from the Sun can be converted to electricity using Photovoltaic Solar Cells.

Kinetic Energy in the Wind

• In Windmills, the kinetic energy of wind gets converted to mechanical energy
• This mechanical energy is used to rotate a turbine to generate electricity.

Energy and Power Efficiency

• Energy and Power efficiency is defined as the percentage of useful energy or power output from a certain amount of energy or power input.
• 
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Renewable and Non-Renewable Energy

Work

• Work done in a process is defined as the amount of energy transferred by that process.
• Mechanical work is defined as the product of the magnitude of force on an object and the distance moved in the direction of the force by the object.
• Work done is a scalar quantity.
• SI Unit is Joules (J).

Power

• Power in its simplest definition is the work done or energy per unit time.
• 
• Power is a scalar quantity.
• SI unit is Watt (W)
• The amount of Work done lifting a object  into the air is
  • 
  • 
  • 
• The amount of power required changes drastically if this work was done over or .
  • 
  •