Work in physics - what is it?

Work in physics is a value that is found by multiplying the modulus of a force that moves a body by the distance that it moves. In the article we will consider in detail situations when the body moves and remains motionless. We learn the formula of work and the units of its measurement.

The forces acting on the body

Imagine that we have a thread on which the body is suspended. From the side of the thread, the elastic force of the thread acts on it, we denote it F. The body is motionless, for example, we attached the thread to a tripod. Do I need to do something to keep this state indefinitely? No. Although the force acts on the body, it does not move.

Work in physics - what is it? Before answering this question, consider the situation. Suppose a body moves, but no forces act on it. For example, if it is a ball in far outer space, away from all stars and galaxies. Then the force of their attraction will be negligible. Let's draw a diagram.

The body moved a certain distance s, but the force is absent (F = 0). Is there any need to take action so that the body continues to move? No. This condition can persist indefinitely. This is a uniform rectilinear motion in the absence of forces acting on the body.

Mechanical force

And now a fundamentally different situation. We will raise the same ball. A force acts on it, it is applied to the body from the side of the rope. The value of the ball’s movement is denoted by the letter s, and the force by F. Will the ball rise itself? No, something should lift it. For example, somewhere the electric motor should work. But in order for it to work, water must fall from the dam, which leads to the rotation of the turbine to which the generator is connected. Through power lines, energy must be transmitted to the engine, and it must work and lift the load. That is, the movement cannot be realized by itself.

Physicists say that in the first two cases, the force does not perform any mechanical work. In the third case, the work is performed. How is it produced? By force F. In physics, work is a quantity. And if so, then it can change up and down. It is easy to guess that if the force is increased and the body moved at the same distance, then the work of this force will be greater. How can you increase strength? For example, taking a ball is two times harder. Then the work will double. Consequently, the work of force is proportional to the magnitude of the force. This is the law.

Formula of mechanical work

Imagine that we need to raise the same ball not by 50 cm, but by 100 cm. We need to do work to raise it first to the first half of the distance, and then to the second. Each time the same work will be done, but the overall work will be twice as much. This means that work is directly proportional to the distance the body moves. Therefore, physicists agreed to designate the quantity F * s with the letter A and call it the work of force. The expression F * s will be directly proportional to the strength and movement of the body.

A = F * s is a formula for working in physics. A is the sought value of the force applied to the body, and s is the path traveled by the body. However, there are situations when the force is applied to the body, but it does not move. In our third case, the body moves in the same direction in which the force is applied. Therefore, it will be more accurate to say that s is the movement of the body in the direction of the force. Let us formulate the definition: work in physics is a quantity equal to the product of the modulus of force and the displacement of the body in the direction of the force.

Units

Let us look at the defining formula A = F * s. [A] = N * m = J. H is Newtons, J is Joules. How to understand what 1 joule is? Let’s draw a diagram on which we depict a force performing work in one joule.

The figure shows the initial and final position of the body. We moved it to a distance of 1 m. When moving to the body, a force of one newton was applied. A = 1 N * 1 m = 1 J. That is, one joule is the work done by a force of one Newton when moving the body, at a distance of 1 m in the direction of the force.

One joule is a little work. To raise a kilogram weight by 10 cm, you need to do work in 1 joule. To raise it to a meter high, you need to do a job of 10 joules. If we talk about the operation of cranes, then they lift tons by tens of meters. Therefore, other measurement units of work are also used: kilojoules, megajoules, etc. 1 kJ = 1000 J, 1 MJ = 10 ^ 6 J. The motor drives the wall clock hand. He does a job far less than one joule. It is measured in millijoules. 1 mJ = 0.001 J. There are microjoules. 1 μJ = 1 * 10 ^ -6 J.