Energy transformations

Click here for a quick lesson on energy and its conversion from one form to another.

We know that energy can not be created or destroyed but it can change from one form into another. We see examples of such transformations every day.

Chemical potential energy and its transformations into other forms of energy are covered in a separate section and will not be covered in this chapter. Click to go to "Transformations of Chemical Potential Energy"

When looking at the energy transformations below it is assumed that no energy is lost in the transformation. In reality this is not true as energy is lost at every step, mainly as heat.

During a roller coaster ride we find transformations of energy between gravitational and kinetic.

At the top of the roller coaster track, the cart has maximum gravitational potential energy. As it falls this is converted to kinetic energy as the cart accelerates downwards. Assuming no friction between the cart and the track, all the gravitational potential energy is converted into kinetic energy at the bottom of the track.

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Consider the weight lifter shown on the right. A few energy transformations are taking place.
All the energy required to lift the weight off the ground comes from chemical energy stored as chemical bonds in the muscles of the weight lifter.

The weight then gains kinetic energy as it moves upwards. At the very top the kinetic energy is converted into gravitational energy.

As the weight is allowed to fall all the gravitational energy is converted back into kinetic energy. The changes are summarised below.

Chemical potential energy=> kinetic energy => gravitational potential energy=> kinetic energy.

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A kettle boiling in an open fire has many transformations some of which are not so obvious. Energy starts in the form of chemical potential energy, in the form of molecules in the gas, and is converted quickly into heat energy by the combustion chemical reaction. Heat then is converted into kinetic energy causing the water molecules to move about with great speed until they become gas, water vapour. The changes are summarised below.

Chemical potential energy=> heat energy => kinetic energy

Where is the kinetic energy most obvious in the video shown on the right?

 

The sport of pole vaulting is an interesting sequence of energy transformations.

The athlete first runs down the track as fast as he/she can possible go.
a) What energy are they maximising by running as fast as possible
b) The energy used by the athlete to run down the track has come from energy stored in the athletes body.
c) When the pole is fully bent the athlete has maximum energy.
d) At the very top of the bar all the energy the athlete had just before leaving the ground has transformed into energy.
e) Assuming no energy loss during the transformations, all the kinetic energy the athlete has as they hit the mat after their jump is
f) What is the relationship between the speed of the athlete just before they leave the ground and the maximum height achieved?

Ancient siege weapons such as the trebuchet were able to harness and transform a huge amount of energy. A heavy counter weight was allowed to fall and propell a heavy projectile towards the enemy. What is the most likely energy transformation taking place?
All energy on Earth has originated from the Sun. We change the many forms of energy into electrical energy to drive our modern cities and to maintain our standard of living. There are many different types of power stations, two of which are coal fired and hydro-electric power plants. Although both coal-fired and hydro-electric power plants use generators to produce electricity it is the method each uses to spin the turbines driving the generators that is different.

Coal fired power stations.

Water from great hights is used to turn the generators of a hydro-electric power station.

It is said that the electrical energy from coal-fired and hydro-electric power plants started as solar energy. Explain. Use the following words in your explanation.
Evaporation, solar energy, photosynthesis, chemical potential energy, heat energy, kinetic energy, condensation, water vapour, electrical energy, gravitational potential energy.

Solution

Continue with energy transformations calculations(gravitational into kinetic)


Click here for some simple exercises involving energy transformation and model planes.

 

Try a worksheet on energy transformation in model rockets.

Activities that junior students can conduct include
Mouse Trap Racers
Model Rockets

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