What Causes Work in Physics?

In summary, work is always done by a force, which has its origin in some other body. In the case of a man pushing a box, the force acting on the box does positive work while the force acting on the man does negative work. This means that the box gains energy while the man loses it. When discussing work, we can choose to say that either body is doing the work, but only one at a time. Typically, we choose to say that the body with the positive work is doing the work.
  • #1
Kyouran
70
10
In physics, work is said to be done by a force. In the field of electricity, work is done by an electrical field. In thermodynamics, work is done by a system. This is kind of confusing and makes me wonder, what is actually the thing that does work? Is it the object, the force field or the force itself?
 
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  • #2
Hi Kyouran,
that is a good question. As you wrote, the work is always done by a force. This force always has its origin in some other body:Imagine man pushing a box on ground from right to left.


BOX MAN
--> <--
-F .. F
<--BOX...


The force acting on the box is [itex]\mathbf{F}[/itex], the force on the man is [itex]-\mathbf{F}[/itex].

Because these are two distinct forces, the have two distinct works.

1) The work of the force acting on the box

When the box has moved to the left by displacement [itex]\mathbf{s}[/itex], the force [itex]\mathbf{F}[/itex] has performed work

$$
W_1 = \mathbf F\cdot \mathbf s
$$

Since the force originates in the man, it is also often said that the man has done the work. In our case it is positive; this means the box has acquired equivalent energy and man has lost it.

2) The work of the force [itex]-\mathbf F[/itex] acting on the man is

$$
W_2 = (-\mathbf F)\cdot \mathbf s
$$

This is negative of the above work. Since the force originates in the box, we can equally say this work has been done by the box.We can choose anyone of the two above alternatives to describe the energy transfer; but only one at a time. Usually we choose that which has positive work, here it is 1).

So, when we say body A (a man) is doing work on body B (a box), we actually mean that there is a force due to body A that has some positive component along the velocity of the body B.
 

1. What is work in physics?

In physics, work is defined as the product of force and displacement. It is a measure of the energy transferred to or from an object when a force is applied over a certain distance.

2. How is work calculated?

The formula for calculating work is W = F * d * cosθ, where W is work, F is the force applied, d is the displacement, and θ is the angle between the force and displacement vectors.

3. What are the units of work in physics?

The standard unit for work in the International System of Units (SI) is the joule (J). However, work can also be measured in other units such as foot-pounds (ft-lb) or calories (cal).

4. What are some examples of work in physics?

Some examples of work in physics include lifting a heavy object, pushing a cart, or stretching a spring. These actions involve applying a force over a distance, resulting in work being done.

5. How is work related to energy?

Work and energy are closely related concepts in physics. Work is the transfer of energy from one object to another. The amount of work done on an object is equal to the change in its energy. This relationship is described by the work-energy theorem: W = ΔE = Efinal - Einitial.

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