Energykinetics it is the form of energy that any body has due to its movement, in other words, it is the form of energy associated withvelocity 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.
Kinetic energy does not depend exclusively on the speed of a body but also on its pasta. Any type of moving body is endowed with this type of energy: translation,rotation,vibration and others. Kinetic energy can be calculated by the following formula:
ANDÇ - kinetic energy (J)
m - body mass (kg)
v - speed (m/s)
See too: Newton's Laws and their applications
what is kinetic energy
THE energykinetics is a modality of energy present in all moving bodies. According to SI, your unit of measure is the joule. Furthermore, this energy is a greatnessclimb which presents exclusively positive values.
THE Kinetic energy is proportional to the square of the body's velocity. 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.
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Work theorem and kinetic energy
The work and kinetic energy theorem states that the work done on a body or particle is equivalent to the variation of its kinetic energy. This theorem can be described using the following equation:
τ - work (J)
ΔAndÇ - variation of kinetic energy (J)
ANDÇF and isÇ0 - final and initial kinetic energy (J)
m - mass (kg)
vF and v0 - final and initial speed (m/s)
Understand this theorem better: the work is the transferinenergy, therefore, when we are pushing a shopping cart, for example, we transfer some of our energy to it. This transferred energy turns into movement, once the cart acquires velocity.
In short, this is what the 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 energykinetics of a body can be diminished in two cases: when it is stored in the form of potential energy, elastic or gravitational, for example; or when there is forcesdissipative able to transform it into other forms of energy, as does the frictional force, which transforms kinetic energy into thermal energy. Therefore, unless there are no dissipative forces, the body's kinetic energy can always return to its initial module, since in that case it will be converted into potential energy without any losses.
In the context of dynamics, there is an important quantity called mechanical energy. This measures all the energy related to the movement that is performed by any body and is calculated by the sum of kinetic energy with potential energy, whatever that sum is.
US conservative systems, where there are no forces like friction, the kinetic and 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 resistance of the air, 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 trigger the vehicle brakes, in this case, we are applying a dissipative force on its wheels, which have their kinetic energy converted into thermal energy.
Deduction of the kinetic energy formula
It is possible to deduce the expression of kinetic energy through the Torricelli equation, one of the kinematics equations that do not use time (t) as one of its variables. Initially it is necessary to isolate the acceleration variable, check:
Then we will use the Newton's 2nd Law, known as the fundamental principle of dynamics. This law states that the net force on a body is equal to the product of its mass and acceleration:
Finally, we will use the definition of work, which states that this can be calculated through the product of force and distance:
See too: Potential energy: know the different forms and what they are for
Kinetic energy of atoms and other particles
THE energykinetics it is a measure of great importance for the study of different physical systems. This energy measure is used to analysis astronomical and for the study of the movement of particles highly energetic, such as the particles that produce cosmic rays or those used in particle accelerators.
In the latter cases, when we calculate the kinetic energy of bodies that have very small masses, it is common for us to use another unit of measure for kinetic energy, the electron volt: one electron volt equals 1,6.10-19 J about.
Relativistic Kinetic Energy
The formula that is classically used to calculate kinetic energy presents limitations: when bodies start to move in speeds close to speed of light (3,0.108 m/s). In this case, it is necessary to apply corrections from the Theory of relativity and related to the inertia of the body (mass).
When any body approaches the speed of light, its inertia tends to increase along with its speed, thus, any body that has any mass will never reach the speed of light. The following image shows the formula of relativistic kinetic energy, check it out:
ç - speed of light (c = 3.0.108 m/s)
Solved exercises on kinetic energy
Question 1) Check the alternative that correctly represents the kinetic energy of a 1000 kg vehicle moving at a constant speed of 3 m/s.
a) 450 J
b) 9000 J
c) 4500 J
d) 900 J
e) 300 J
Feedback: Letter C
Resolution:
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 and mark the correct alternative.
a) 20 m/s
b) 40 m/s
c) 200 m/s
d) 3 m/s
e) 10 m/s
Template: Letter a
Resolution:
To solve the exercise, just apply the data informed in the kinetic energy formula:
Question 3) A piece of furniture has kinetic energy AND and speed v. At a given time, the speed of this mobile becomes 3v and its mass remains constant. The alternative that presents the new kinetic energy of this piece of furniture is:
a) 3 AND
b) 9 AND
c) 4.5 AND
d) 10 AND
e) E/3
Feedback: Letter B
Resolution:
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.
By Me. Rafael Helerbrock
