Everyone understands that work is a kind of social activity of a person that he needs to ensure his existence. However, in physics there is also a similar concept that has a completely different meaning. What is work in physics, this article will answer.
Work as a physical quantity
Answering the question of what work is in physics, it should be clarified that this is the energy that is spent on performing any action. For example, a person transfers a load from one place to another, while he does work against friction forces. If this person begins to lift the load, then his work will be aimed at overcoming the gravitational force of the planet. Another example: the gas under the piston, as a result of heating, begins to increase its volume, in which case it is said that it does some work.
In all the above cases, there is one common feature: the work differs from zero only when there is some type of mechanical movement of objects or their parts(movement of worker with load, expansion of gas).
Thus, work is the process of transferring energy from one state to another for a given body, as a result of which this body changes its position in space.
Work formula
Now let's show how to quantitatively calculate the value under study. The transfer of energy between different states is only possible if some force is present. This can be the physical effort of human hands and feet, the force of machines, the pressure created, which is easily converted into force, in the event of combustion of fuel in a cylinder, the force of electromagnetic induction of an electric motor, and so on.
The following formula will answer the question of how to find a job in physics:
A=(F¯l¯)
Work A is a scalar quantity, while force F¯ and displacement l¯ are vector quantities. That is why the formula for calculating A uses parentheses to show that we are talking about the scalar product of vectors. In scalar form, the above expression can be rewritten as follows:
A=Flcos(φ)
Here φ is the angle between force vectors F¯ and displacement l¯.
Since displacement is measured in meters and force is in Newtons, the unit of work is Newton per meter (Nm). The SI unit has its own name, the joule (J). It turns out that work of 1 J corresponds to a force of 1 N, which, acting along the direction of displacement, moved the body by1 meter.
Gas work
We analyzed the question of what mechanical work is in physics, and gave a formula by which it can be calculated. In the case of expanding gases, however, a different expression is used.
Assume that we have a gas system that fills the volume V1 and is under pressure P. Let its volume change as a result of some external or internal influence on the system and became equal to V2. Then the work of gas A can be determined by the following formula:
A=∫V(P(V)dV)
If you plot the P(V) function in the P-V axes, then the area under the curve will be numerically equal to A.
In the case of an isobaric process (P=const) for an ideal gas, the answer to the question of how to find work in physics will be the following simple expression:
A=P(V2-V1)
If as a result of a thermodynamic process the volume of gas does not change, then its work will be equal to zero. If V2>V1, then the gas does positive work if V1>V 2, then negative.
Work of moment of force
The moment of force is a physical quantity, which is expressed by the following formula:
M=[F¯r¯]
That is, M is equal to the vector product of the force F and the radius vector r about the axis of rotation. The moment of force is expressed in Nm.
What is the work of a moment of force in physics? To this questionthe following formula will answer:
A=Mθ
This equality means that if the moment M, acting on the system, causes it to rotate around the axis by an angle θ, then it does work A. The angle θ here must be expressed in radians to get the work in joules.
The calculation of the work of the moment of force plays an important role in all mechanical systems where there is rotation, such as wheels, gears, shafts and so on.
Work of gravity
Having figured out what work is in physics, let's calculate this value for the forces of gravity. Suppose a body of mass m falls from a height h. Since gravity F acts vertically downward, it does positive work. It is determined by the following formula:
A=mgh, where F=mg
Many in the obtained formula for the quantity A can see an expression for the potential energy of a body in the field of gravitational forces. During the fall of the body, gravity does the work of transferring the potential energy of the body into the kinetic energy of its movement.
