What is kinetic energy

In this article we will read about kinetic energy, its formulae, examples etc. So first you should know-

what do you mean by kinetic energy?

Kinetic energy is the type of energy that is related to movement. Every moving body is endowed with kinetic energy, which is a scalar quantity measured in joules.

Other definition of kinetic energy

Kinetic energy is the form of energy that any body has because of its motion. Or you can say, it is the form of energy associated with the velocity of a body. 

When we apply a non-zero net force on some body, we are doing work on it, so it acquires kinetic energy as its speed increases.

You should also know that kinetic energy does not depend exclusively (0nly) on the speed of a body but also on its mass. 

Any type of moving body is endowed with this type of energy: translation, rotation, vibration and others. Kinetic energy can be calculated with the help of following formula:

C – kinetic energy (J)

m – body mass (kg)

v – speed (m/s)

Different Types of kinetic energy:

If we talk about how many types of kinetic energy, then remember, kinetic energy can be divided into three types depending on the type of movement of the object. Below are the different types of kinetic energy:

  1. Translational kinetic energy : This is the energy due to movement from one position to another. For example, a train moving on railway lines, or objects freely falling under the action of gravity, have translational kinetic energy. 
  2. Rotational Kinetic Energy : Energy generated by rotational motion. For example- The rotation of the Earth is an excellent example of rotational kinetic energy. 
  3. Oscillatory kinetic energy: is energy due to vibrational motion. For example- Tuning fork movement is a prime example of vibrational kinetic energy.

What is kinetic energy measured in?

According to the SI (standard unit), its unit of measure is the joule. Because it is an energy and we do measure energy in joule. Furthermore, this energy is a scalar quantity that has only positive values.

Important point:- The kinetic energy is proportional to the square of the body speed. So, if the speed of a body doubles, its kinetic energy will increase four times, if the speed of a body triples, then this increase will be nine times.

Kinetic energy: Solved exercises & example 

Question 1) What is the kinetic energy of a vehicle with a mass of 1000 kg that moves at a constant speed of 3 m/s?

a) 450 J

b) 9000 J

c) 4500 J

d) 900 J

e) 300 J

Answer : C


To resolve the issue, just use the kinetic energy formula and replace the data informed in the exercise statement, check:

Question 2) It is known that the kinetic energy of a body is 2000 J and its mass is 10 kg. Determine how fast this body moves?

a) 20 m/s

b) 40 m/s

c) 200 m/s

d) 3 m/s

e) 10 m/s

Answer : A


To solve the exercise, just apply the data informed in the kinetic energy formula:

Question 3) A particle has kinetic energy E and velocity v . At a given time, the speed of this particle becomes 3v and its mass remains constant. What will be the new kinetic energy ?

a) 3 times

b) 9 times

c) 4.5 times

d) 10 times

Answer : B


As we know, kinetic energy depends on the square of velocity, so when velocity is tripled, that energy must increase by a factor of nine times.

5 Examples of kinetic energy

Let’s take a look at a 5 best examples of kinetic energy to make it clearer:

  1. Person on a motorcycle: we see that they experience an increase in both potential energy (as they move upward) and in kinetic energy (as their speed increases). A heavier person will be able to acquire more kinetic energy if the motorcycle allows him to move faster.
  2. A phone that falls to the ground : This type of example is very important in understanding kinetic energy. Energy builds up in your body as it descends, and is completely released when it breaks free from hitting the ground. This is the first hit that starts generating kinetic energy. The rest of the kinetic energy is acquired by the gravity of the Earth.
  3. Ball hitting : A case similar to what happens with a phone. The ball at rest finds equilibrium, and kinetic energy begins to be released from the moment we hit it. The heavier and larger the ball, the more effort it will take to stop or move it.
  4. When we throw a stone from a slope: As the rock descends the slope, its kinetic energy increases. Energy will depend on the mass and the rate at which it falls. This, in turn, will depend on the bias.
  5. Roller coaster: Amusement parks are the key to explaining kinetic energy. On a roller coaster, the car gains kinetic energy when it falls and increases its speed.

I hope that with these five examples of kinetic energy, the concept and its use will become clearer to you.

More Examples of Kinetic Energy-

Еvеn іf уоu аrе nоt а fаn оf thе gаmе оf bіllіаrdѕ, уоu knоw thаt іt соnѕіѕtѕ іn uѕіng а ѕtісk tо рut а bаll оf уоur сhоісе іn а сеrtаіn hole, whісh gіvеѕ уоu аn аdvаntаgе оvеr уоur орроnеnt. Yоu роіnt thе ѕtісk аt thе bаll уоu аrе wоrkіng wіth аnd rеіnfоrсе іt tо thе dеѕіrеd hole. 

Тhе bаll іѕ саrrіеd tоwаrdѕ hіm, whісh mаkеѕ а mоvеmеnt. Іtѕ mоvеmеnt іѕ thе rеѕult оf уоur “wоrk”, whісh іѕ соnvеrtеd іntо kinetic еnеrgу (КЕ) fоr thе bаll. Тhіѕ іѕ thе rеаѕоn whу КЕ іѕ mеаѕurеd іn јоulеѕ (Ј) , whісh іѕ thе unіt оf mеаѕurеmеnt іn wоrk рhуѕісѕ.

Ву nоw уоu ѕhоuld hаvе mоrе оr lеѕѕ gоt аn іdеа оf ​​whаt kіnеtіс еnеrgу іѕ аnd іt’ѕ tіmе tо lооk аt whаt wе nееd іt wіth аnd whеrе іt іѕ uѕеd іn оur dаіlу lіvеѕ.

Кinetic energy іn thе hеаtіng

Тhіѕ іѕ thе ѕо-саllеd rаdіаnt еnеrgу, whісh рlауѕ аn ехtrеmеlу іmроrtаnt rоlе іn thе рrоduсtіоn оf аll kіndѕ оf hеаtіng аррlіаnсеѕ: соnvеrtеr ѕtоvеѕ, tоаѕtеr mасhіnеѕ, mісrоwаvе оvеnѕ, аѕ wеll аѕ іn а numbеr оf оthеr rаdіаtоrѕ. 

Іnfrаrеd rаdіаtіоn іѕ wіdеlу uѕеd іn mеdісіnе (wаrmіng nеwbоrnѕ іn іnсubаtоrѕ, dіаgnоѕіng bіоlоgісаl mоlесulеѕ, wаrmіng thе humаn bоdу thrоugh rаdіаtіоn, еtс.), іn рhуѕіоthеrару (іnfrаrеd ѕаunаѕ), fоr сlеаnіng hіѕtоrісаl mоnumеntѕ аnd еvеn fоr nіght vіѕіоn. оf mоvіng оbјесtѕ аnd оbјесtѕ іn thе dаrk.

Кinetic energy fоr еlесtrісіtу

Тhеrе аrе аlѕо mаnу ехаmрlеѕ hеrе, but kinetic energy іѕ wіdеlу uѕеd fоr lіghtіng . А tурісаl ехаmрlе іѕ thе ѕеnѕоr lаmрѕ, whісh turn оn whеn thеу ѕеnѕе аnу mоvеmеnt. 

Вut еlесtrісіtу іѕ аlѕо nееdеd whеn thе dооrbеll rіngѕ, whеn wе wаnt tо lіѕtеn tо muѕіс (hеаdрhоnеѕ аnd аudіо ѕреаkеrѕ) оr еvеn whеn wе wаtсh ТV.

Кinetic energy аnd ѕоund еnеrgу

Dо уоu рrеfеr tо lіѕtеn tо thе gruntіng оf а ріg аnd thе сrоаkіng оf frоgѕ оr dо уоu еnјоу thе ѕоng оf сrісkеtѕ оr nіghtіngаlеѕ. Wеll, іt’ѕ а mаttеr оf реrѕоnаl dеѕіrе, but аll thеѕе ѕоundѕ аrе аn ехаmрlе оf ѕоund еnеrgу.

Кinetic energy аnd thеrmаl еnеrgу

Тhеrmаl еnеrgу іѕ whаt mаkеѕ uѕ wаrm-blооdеd аnd асtuаllу еntіtlеѕ аll mаmmаlѕ оn оur рlаnеt tо ехіѕt. Іt саn bе fоund іn thеrmаl ѕрrіngѕ аnd gеуѕеrѕ, аѕ wеll аѕ іn а сuр оf hоt сhосоlаtе.

Кinetic energy аnd mесhаnісаl еnеrgу

Тhіѕ іѕ thе whіѕtlіng оf thе wіnd, thе murmur оf mоuntаіn ѕtrеаmѕ, thе саr mоvіng dоwn thе ѕtrееt оr thе fіѕh ѕwіmmіng іn thе rіvеr. Аll thіѕ іѕ mесhаnісаl еnеrgу, whісh іѕ аlѕо а kіnd оf kіnеtіс еnеrgу.

Work theorem and kinetic energy

The work and kinetic energy theorem states that work done on a body or particle is equivalent to the change in its kinetic energy . This theorem can be described using the following equation:

  • τ – work (J)
  • ΔE C – variation of kinetic energy (J)
  • F and E 0 – final and initial kinetic energy (J)
  • m – mass (kg)
  • F and 0 – final and initial speed (m/s)

Understand this theorem better: you should know that the work is the transfer of energy. 

So when we are pushing a shopping cart in shopping mall, for example, we transfer some of our energy into it. This transferred energy transforms into movement as the cart acquires speed.

In short, work and kinetic energy theorem says:

The transfer of energy to some system, through the application of a force, is called work, which, in turn, is equivalent to changing the kinetic energy of that system.

Kinetic energy loss

The kinetic energy of a body can be decreased in two cases: 

When it is stored in the form of potential, for example: elastic or gravitational energy. 

Or when there are dissipative forces capable of transforming it into other forms of energy, as does the friction force. Which transforms kinetic energy into thermal energy. 

Therefore, unless there are no dissipative forces, the kinetic energy of the body can always return to its initial modulus, since in that case it will be converted into potential energy without loss.

Within dynamics, there is an important quantity called mechanical energy (you probably heard this). 

Mechanical energy measures all the energy related to the movement that is performed by any body and is calculated by the sum of the kinetic energy with the potential energy, whatever that sum may be.

In conservative systems, where there are no forces such as friction, the kinetic & potential energies are interchangeable. When there are additions to one of the two, the other decreases accordingly, so that their sum is always constant.

However, in dissipative systems, in which there are forces applied to the air resistance, the kinetic energy and the potential energy can be reduced. The energy difference in this case is the energy that is absorbed in the form of heat, vibrations, sound waves, etc. 

A simple example of this type of situation is what happens when we activate the brakes of a vehicle, in this case, we are applying a dissipative force on its wheels, which have their kinetic energy converted into thermal energy.

More about kinetic energy

You have now know that the kinetic energy is a form of energy that can be the key to reducing energy expenditure. 

So now we are going to talk to you about how it is generated, how it can be transformed into electricity and how it can be very useful for transportation. Don’t stop reading!

How kinetic energy is produced

Kinetic energy is that which a body possesses due to its motion and depends on its mass (m) and speed (v), which means, it is produced by the movement itself. 

Therefore, to calculate it, both metrics come into play. Once the kinetic energy is generated, it is maintained until the body changes its speed.

Transformation of kinetic to electrical energy

The energy that is released by the movement of bodies can be used to generate electricity or heat, an example of the passage from kinetic energy to electrical energy would be the dynamo of the bicycle. 

The movement of the wheel makes the dynamo rotate and as a result the bike (cycle) light comes on. In this case, energy is obtained when you brake releasing in the form of heat. In electric bicycles this energy can be recovered to recharge the battery.

Within renewable energies, specifically the operation of wind energy is based on the transformation of kinetic energy into electrical energy by the movement of the wind turbine blades. 

The hydraulic energy , on the other hand, is based on converting the potential energy of water falling into kinetic energy by moving a turbine that generates electricity.

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