Kinetic energy is the energy that an object possesses as a result of its motion. Kinetic energy is defined as the work necessary to accelerate an object from a state of rest to its current speed. This energy is gained through acceleration and the object maintains its energy level unless its speed changes, often occurring naturally even through regular air resistance as the object travels.
Perhaps one of the best ways to understand kinetic energy is to look at examples to demonstrate how such energy can be changed into and from other various forms of energy. One of the most ubiquitous examples of this in everyday life is that of a cyclist using the chemical energy provided by food in order to pedal and thus accelerate a bicycle in order to allow it to reach particular speed. Once the cyclist reaches a certain speed this speed can be easily maintained without much further effort, although more may be required in order to counter air-resistance and normal friction upon the road. Thus chemical energy has been changed into kinetic energy and the bicycle is put into motion. This process, however, is not totally efficient, as the cyclist also produces heat.
The kinetic energy produced in this way can also be changed into other forms. If the cyclist comes to a hill that is fairly steep and comes to a stop at the top of the hill all of the kinetic energy is mostly converted into potential energy thanks to gravity – most of which can be tapped and released by cycling free-wheel down the reverse side. As the bicycle will lose part of its original energy because of friction it will require further pedaling in order to regain all of its original speed. Another example of changing kinetic energy into other forms via a bicycle is shown by cyclists attaching dynamos to their bicycles liked to front and rear lights. The pedaling motion that produces kinetic energy is transformed via the dynamo into the electrical energy necessary to power the lights.
Another example is the way in which spacecraft use refined chemical energy in order to lift off, thus gaining sufficient kinetic energy to orbit effectively and maintain its orbit. The kinetic energy that the craft gains during its launch remains unchanged whilst the craft is in orbit due to the fact that friction is almost totally absent. The energy becomes apparent (and visible) during the craft’s re-entry process, however, when the craft’s kinetic energy is then converted back into heat.
It is also possible for kinetic energy to be transferred from one object in motion to another as well. Take snooker, for instance, where a player gives the cue ball kinetic energy by hitting it with his cue. When the ball hits another ball on the table it will slow down, and the ball it hits will accelerate as the kinetic energy is transferred to it. In this case kinetic energy is successfully preserved from the transfer and this is known as an elastic collision. This is different to an inelastic collision where the kinetic energy is then dissipated as, for example, heat or sound.
(Energy FAQ Series)
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