# Q&A: How Does Work & Energy Relate to Solids, Liquids & Gases?

• Sarah0001
In summary, this statement is incorrect because any loading that involves the deformation of a solid, liquid, or gas automatically involves doing work on or by the substance.
Sarah0001
Homework Statement
"If the volume of the substance does not change, no work is done on or by the substance"
Relevant Equations
ΔU = W+ Q
work=−PΔV
I can understand how this applies to gases as in that scenario work done = pressure * change in volume and if change in volume is zero then W=0
so change in internal energy = Q. But I do not understand how this applies generally to all types of substances, say solid, liquid and gas.

It applies simply to solids, liquids and gases that e.g. in a container or otherwise fixed position where their volume may change, in the presence of an external atmosphere.
It does not apply to a mechanical arm connected to a motor that is able to do work on an object to set it in motion.
Perhaps others can help to answer to this question, because I don't know that I have answered it satisfactorily. @Chestermiller might you have an input here?

Sarah0001 said:
I can understand how this applies to gases as in that scenario work done = pressure * change in volume and if change in volume is zero then W=0
so change in internal energy = Q. But I do not understand how this applies generally to all types of substances, say solid, liquid and gas.
You don't understand the statement because it is obviously incorrect. Any loading that involves the deformation of a solid, liquid, or gas automatically involves doing work on or by the substance. Examples of this are stirring, shearing between parallel plates, forcing through a pipe, etc., ad infinitum. It does not only apply to volume changes. In addition to this, even without deformation, the substance can still experience a change in kinetic energy and/or kinetic energy, which is the result of doing work on or by the substance.

Chestermiller said:
You don't understand the statement because it is obviously incorrect. Any loading that involves the deformation of a solid, liquid, or gas automatically involves doing work on or by the substance. Examples of this are stirring, shearing between parallel plates, forcing through a pipe, etc., ad infinitum. It does not only apply to volume changes. In addition to this, even without deformation, the substance can still experience a change in kinetic energy and/or kinetic energy, which is the result of doing work on or by the substance.
Thank you very much @Chestermiller I didn't know the complete answer, but that's exactly the kind of input I was looking for. Many thanks!

## What is work and energy?

Work and energy are two fundamental concepts in physics. Work is defined as the force applied to an object multiplied by the distance the object moves in the direction of the force. Energy, on the other hand, is the ability to do work or cause a change in an object's state or motion.

## How do work and energy relate to solids, liquids, and gases?

In solids, work and energy are related through the concept of elastic potential energy. This is the energy stored in an object as a result of its shape or position. In liquids, work and energy are related through the concept of fluid pressure. This is the force exerted by a liquid on an object and is related to the depth of the liquid and its density. In gases, work and energy are related through the concept of gas pressure. This is the force exerted by gas molecules on the walls of a container and is related to the number of gas molecules and their speed.

## How is work and energy calculated in these states of matter?

In solids, work and energy can be calculated using the formula W = F * d, where W is work, F is force, and d is distance. In liquids, work and energy can be calculated using the formula W = P * A * d, where W is work, P is pressure, A is the area of the object, and d is the depth of the liquid. In gases, work and energy can be calculated using the formula W = -P * ΔV, where W is work, P is pressure, and ΔV is the change in volume.

## How is energy transferred in these states of matter?

In solids, energy can be transferred through heat, sound, or mechanical waves. In liquids, energy can be transferred through convection or conduction. In gases, energy can be transferred through convection, conduction, or radiation. In all states of matter, energy can also be transferred through work, as discussed earlier.

## How do these concepts apply to real-world situations?

Work and energy are present in almost all aspects of our daily lives. For example, the energy from the sun is transferred to the Earth as light and heat, which is then used by plants to do work through photosynthesis. In our bodies, the conversion of food into energy is essential for our survival. In industrial processes, work and energy are used to power machines and produce goods. Overall, understanding the relationship between work and energy in different states of matter is crucial for understanding and manipulating our physical world.

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