The Law of Conservation of Energy: Life’s a Roller Coaster!

A photograph showing buddhist monks enjoying the scary thrills of a roller coaster ride. The Law of Conservation of Energy: Life's a roller coaster! - NaturPhilosophieWhat is Energy?

And what does the Law of Conservation of Energy actually mean?  In science and Nature, the word ‘energy’ conjures up a wealth of images associated with speed of movement, activity and work.  Energy does appear in many guises.  Even matter is a form of energy.  Actually, everything in the Universe is nothing more than energy in one form or another… 

We are familiar with many forms of ‘energy‘:

  • the energy carried by electromagnetic radiation (as light or heat),
  • the energy of chemical reactions (from plant photosynthesis to fossil fuel burning)
  • the electrical energy that flows on tap in our dwellings, at least for a privileged few of the World population
  • the mechanical energy resulting from the use of chemical, electrical or hydraulic energy.

 

A picture showing a domino cascade.Energy Transfers

In a system, energy transfers take place when energy stays in the same form, but is passed between different objects.  For example, think of a row of dominoes.  The mechanical energy of the first domino is transferred to the mechanical energy of the next domino and so on.  The energy remains mechanical in nature, as it is passed on from one domino unto another.

 

Transformations of Potential Energy and Kinetic Energy in a Roller Coaster

A diagram showing the Energy Rollercoaster and its changes in potential energy and kinetic energy at different stages of the roller-coaster journey on the fairground track. Source: Wikispaces.
http://fzxxprj.wikispaces.com/

Energy transformations occur within a system when energy changes into its different forms.  Energy transformations can occur within an object, or between objects.

Think about the engine in a car.  The chemical energy of the fuel is transformed into the thermal and mechanical energy of the motor and tires.

roller coaster is composed of a related set of components, some of which are physical objects, such as the car and track, and the tires.  Other parts of this system are processes, such as the car’s movement and the associated energy transfers and transformations.

Even though a roller coaster car slows down as it moves up along the track, its energy is not being destroyed.  Actually, energy is neither created nor destroyed within a system.

 

Energy is only transferred or transformed.

And this is the bit you must always remember!!

 

As the roller coaster car goes up the track, its kinetic energy is gradually converted to gravitational potential energy.  As the roller coaster car races down each hill, the gravitational potential energy is transformed into mechanical, sound and thermal kinetic energy.

Try the Roller Coaster Simulation for yourself.

 

Energy Transformations of Throwing up Books in Sheer Frustration

Ever felt like you are running out of energy over your Maths and Science problems?  Ever felt like throwing all your Maths and Science books up in the air, because you just could not see the wood for the trees?  No?  Just me, then…  🙂

Meantime, throwing up a book or another object up in the air provides another perfect example for understanding what is meant by the conservation of energy, by illustrating the different ways in which energy gets transformed throughout the situation.

Look at this picture.

See what I mean?

 

Energy Transformations

A cartoon showing a student throwing a book up in the air in frustation. The student thinks about the motion and the energy of the book at different stages: "Chemical energy -> Kinetic energy -> Gravitational energy -> Kinetic plus Gravitational energy -> Sound energy -> Internal energy".It starts as chemical energy stored in the muscles of the unruly student’s arm.  Chemical reactions associated with muscle contraction release some of this energy.  This becomes the energy of motion, or kinetic energy, of the student’s hand and book.  And like the roller coaster car…

As the book rises, it slows down and its kinetic energy decreases.  But the kinetic energy is not destroyed.  Instead it is converted into another form of energy, called gravitational energy.

The gravitational potential energy of the book is converted back into kinetic energy as the book falls down.

Energy is released as sound.  When the book strikes the ground, it makes a noise.

And if the temperature of the ground and the book were to be measured precisely after the impact, a slight increase in temperature would be recorded in both.  An increase in temperature in any substance is associated with the increase of the internal energy of its molecular constituents.

 

A cartoon showing Asterix punch a Roman.The same principle can be applied elsewhere.  Another short, but always memorable, example of energy transformations is provided by one of my favourites fictional character.

Now you have a go!  Write down how the energy is transferred and/or transformed in the following situation.  Here Asterix The Gaul has a brief and brutal encounter with one of the Romans…

Those are excellent examples of energy transformations in a system under the Law of Conservation of Energy

 

The Law of Conservation of Energy

In 1789, French scientist Antoine de Lavoisier formulated  this fact in his “Traité Élémentaire de Chimie“, as what is being taught in French schools as Lavoisier’s Law: “Nothing is lost, nothing is created.  Everything is transformed.”

As we have seen, energy is not destroyed.  Energy is merely transferred or transformed.  That is exactly what the Law of Conservation of Energy is all about.  The energy of a system remains within that system, so that

E_{initial} = E_{final}.

 

Crucial to the development of the modern energy conservation principle was the demonstration of the mechanical equivalent of heat.  In 1798, Benjamin Thompson performed measurements of the frictional heat generated in boring cannons and developed the idea that heat is a form of kinetic energy.  In 1841, a German surgeon, Julius Robert von Mayer, formulated one of the original statements of the conservation of energy, what is now known as one of the first versions of the first law of thermodynamics.  He discovered that heat and mechanical work were both forms of energy.

 

Nothing is lost, nothing is created.

Everything is transformed.

 

Meanwhile, in 1843, James Prescott Joule discovered the mechanical equivalent in a series of independently-led experiments.  With a simple apparatus, he demonstrated that the gravitational potential energy lost by a descending weight was equal to the thermal energy (heat) gained by water by friction with a paddle.  In the end, Joule drew the wider recognition for his discovery.

In 1844, William Robert Grove postulated a relationship between mechanics, heat, light, electricity and magnetism, and later published his theories in his book “The Correlation of Physical Forces“.

 

Harvesting Energy from Nature…

The London Array is arguably the most widely known UK offshore wind farm, notorious by the scale of its installation and its proximity to Greater London.  Its 175 turbines can generate enough energy to power nearly half a million UK homes and reduce harmful  CO2 emissions by over 900,000 tonnes a year, equivalent to the emissions of about 300,000 vehicles.  The London Array has been constructed with the aim of making a big difference to the environment, as well as helping provide a reliable electricity supply to south-east England.  The London Array wind farm started producing electrical energy at the end of October 2012.

Besides wind energy, projects for onshore hydroelectric power plants are also planned to harness the natural energy from sea waves and tides.

A photographic collage showing the London Array, the Gemasolar power plant and a potential example of onshore hydroelectric generation. Image: NaturPhilosophie
The London Array (left), an example of an onshore hydroelectric power plant, and the Gemasolar power plant in Spain (bottom right)

The Gemasolar thermosolar plant is the world’s first commercial-scale solar plant to use a central solar power tower receiver, heliostat field and molten-salt heat transfer fluid and energy storage system.

Gemasolar is located in the province of Seville, Spain.  It consists of a 185-hectate solar field that has a 140-metre high tower receiver, a power island and 2650 heliostats, each 120 m2 and distributed in concentric rings around the tower.  Gemasolar can supply 110 GigaWatts hour per year – enough to supply power to 27,500 homes.

 

Designing Energy Solutions for a Bright Future

Nowadays, the Law of Conservation of Energy does not only help engineers design hair-raising roller coaster rides, it also helps scientists forecast tsunamis and even study the Solar system.

Expanding upon the Law of Conservation of Energy, Albert Einstein established that matter can be considered as a form of energy.  We see this in nuclear fusion reactions where matter is transformed into thermal and electromagnetic energy.

A collage showing an illustration of the nuclear fusion process and the photograph of a fusion reaction target chamber. Image: NaturPhilosophie
The Nuclear Fusion Process and a Fusion Reaction Target Chamber

Although practical research has been taken place in that domain, stable energy generation from nuclear fusion will remain out-of-reach for another few years.  But we are beginning to see projects taking shape.

With 500 Megawatts of energy theoretically obtainable from only half a gram of hydrogen, the hunt for fusion power generation heats up…