Everyone understands that work is a kind of social activity of a person that he needs to ensure his existence. Nevertheless, in physics there is also a similar concept, which has a completely different meaning. What is work in physics, this article will answer.
Work as a physical quantity
When answering the question of what work in physics is, it should be clarified that this is energy that has been expended in the commission of any action. For example, a person transfers cargo from one place to another, while he does work against friction. If this person begins to lift the load, then his work will be aimed at overcoming the planet’s gravity. 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 these cases, there is one common feature: work differs from zero only when there is some type of mechanical movement of objects or their parts (movement of a worker with a 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 we show how to quantitatively calculate the studied value. The transfer of energy between different states is possible only if some force is present. This can be the physical effort of human hands and feet, the power of machines, the pressure created, which is easily converted into force, in the case of fuel combustion in a cylinder, the force of electromagnetic induction of an electric motor, and so on.
When asked how to find work in physics, the following formula will answer:
A = (F¯ * l¯)
Work A is a scalar quantity, in turn, the force F¯ and the displacement l¯ are vector quantities. That is why the formula for calculating A uses parentheses to show that it is a scalar product of vectors. In scalar form, the expression above can be rewritten as follows:
A = F * l * cos (φ)
Here φ is the angle between the vectors of force F¯ and displacement l¯.
Since displacement is measured in meters and force in Newtons, the unit of work will be Newton per meter (N * m). In SI, this unit has its own name - joule (J). It turns out that the work of 1 J corresponds to a force of 1 N, which, acting along the direction of displacement, moved the body 1 meter.
Gas operation
We examined the question of what mechanical work is in physics, and presented a formula by which it can be calculated. In the case of gas expansion, however, a different expression is used.
Suppose we have a gas system that fills the volume V 1 and is under pressure P. Let its volume change as a result of any external or internal influence on the system and become equal to V 2 . Then the work of gas A can be determined by the following formula:
A = ∫ V (P (V) * dV)
If we plot the function P (V) in the PV axes, 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 is the following simple expression:
A = P * (V 2 -V 1 )
If the gas volume does not change as a result of the thermodynamic process, then its work will be zero. If V 2 > V 1 , then the gas does a positive job, if V 1 > V 2 then negative.
Work of the moment of force
A 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 by the radius vector r relative to the axis of rotation. The moment of force is expressed in N * m.
What is the work of a moment of force in physics? The following formula will answer this question:
A = M * θ
This equality means that if the moment M acting on the system leads to its rotation around the axis by the angle θ, then it does the work A. The angle θ here must be expressed in radians in order to get 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, for example, wheels, gears, shafts and so on.
Gravity Work
Having figured out what work is in physics, we calculate this value for gravitational forces. Suppose that a body of mass m falls from a height h. Since the force of gravity F acts vertically down, it does a positive job. It is determined by the following formula:
A = m * g * h,
where F = m * g
Many in the obtained formula for the quantity A can see the expression for the potential energy of a body located in the field of gravitational forces. During the fall of the body, gravity does the work of translating the potential energy of the body into the kinetic energy of its movement.