Work in physics - what is it?

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Work in physics - what is it?
Work in physics - what is it?

Work in physics is a value that is found by multiplying the module of the force that moves the body by the distance it has moved. In the article, we will consider in detail the situations when the body moves and remains motionless. Let's learn the formula of work and its units of measurement.

Forces acting on a body

Let's imagine that we have a thread on which a body is suspended. From the side of the thread, the elastic force of the thread acts on it, let's denote it F. The body is motionless, let's say we attached the thread to a tripod. Is it necessary to do something to keep this state indefinitely? No. Although there is a force acting on the body, it does not move.

Force acting on the body

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

The body has moved a certain distance s, but there is no force (F=0). Is it necessarytake any action to keep the body moving? No. This state can be maintained indefinitely. This is uniform rectilinear motion in the absence of forces acting on the body.

Force producing mechanical work

Body in motion

And now the situation is fundamentally different. We will raise the same ball. A force acts on it, it is applied to the body from the side of the rope. We denote the amount of movement of the ball by the letter s, and the force - F. Will the ball itself rise? No, something has to lift it. For example, an electric motor must work somewhere. 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 the power line, 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 no mechanical work. In the third case, the work is done. What 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 is moved the same distance, then the work of this force will be greater. How can strength be increased? For example, taking a ball is twice as hard. Then the work will double. Therefore, the work done by a force is proportional to the magnitude of the force. This is the law.

Mechanical work formula

Let's imagine that we need to raise the same ball not by 50 cm, but by 100 the work to lift it first to the first half of the distance, and then to the second. Each time the same work will be done, but the total work will be twice as much. This means that work is directly proportional to the distance traveled by the body. Therefore, physicists agreed to denote the value of Fs by the letter A and call it the work of force. The expression Fs will be directly proportional to the force and displacement of the body.

A=Fs is the formula for working in physics. A is the desired value of the force applied to the body, and s is the path traveled by the body. However, there are situations when a force is applied to the body, but it does not move. In our third case, the body moves in the same direction as the force is applied. Therefore, it would be more accurate to say that s is the displacement of the body in the direction of the force. Let's formulate a 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 of measure

Let's look at the defining formula A=Fs. [A]=Nm=J. N is newtons, J is joules. How to understand what 1 joule is? Let's draw a diagram showing a force doing work of one joule.

Work in 1 joule

The figure shows the initial and final position of the body. We moved it to a distance of 1 m. When moving, a force of one newton was applied to the body. A \u003d 1 N1 m \u003d 1 J. That is, one joule is the work done by a force of one newton when a body moves at a distance of 1 m in the direction of the force.

One joule is a small amount of work. To raise1 kg weight per 10 cm, you need to do work in 1 joule. To raise it to a meter height, you need to do work of 10 joules. If we talk about the work of cranes, they lift tons by tens of meters. Therefore, other units of measurement of work are also used: kilojoules, megajoules, etc. 1 kJ=1000 J, 1 MJ=10 ^ 6 J. The hand of the wall clock is set in motion by the motor. It does work much less than one joule. It is measured in millijoules. 1 mJ=0.001 J. There are also microjoules. 1 μJ=110^-6 J.

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