# Physics - Classical Mechanics - Internal Energy and Work

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## Introduction

Hey it's a me again @drifter1! Today we continue with Physics and more specifically the branch "Classical Mechanics" to talk about Internal Energy and Work. So, without further ado, let's get straight into them!

## Internal Energy

Talking about the Physics branch which is called "Thermodynamics", Internal energy is defined as the property or state that a specific substance has on absence of capillarity (the tendency of a liquid to rise or fall as a result of surface tension) and external electric, magnetic or other types of fields. That way, according to the first law of thermodynamics, any change that a system undergoes is the result of some work, with this work being equal to the change in internal energy. Sometimes this internal energy can be represented as the sum of kinetic, potential and chemical energy. That's exactly why I wanted to cover this topic :)

Let's now think about a glass of water that's standing still on top of a table. Let's suppose that we don't move this glass, which means that there will be no change in kinetic energy (KE = 0) and that potential energy can be considered zero (PE = 0). Does this glass have any energy now? Yes, it has chemical energy, which happens in the microscopic scale and is caused by the random, disordered motion of the water's molecules. So, there's surely no apparent energy in the macroscopic scale, but thinking about the microscopic scale we understand that there's some microscopic kinetic energy caused by the motion of the molecules and also some microscopic potential energy caused by the attractive and repetitive forces between the water molecules.

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## Internal Work

Talking about any physics system there will be forces that are exerted by the surroundings (external) and also forces which are part of the same system (internal). For these two kinds of forces we define the corresponding terms of external work and internal work. This categorization is very important as it helps us understand which forces are conservative and which not (non-conservative).

Simplifying the whole topic we can say that external forces include the applied force, normal force, tension force, friction force and air resistance force. In the same notion, internal forces include the gravity force, magnetic force, electric force and spring force, which as you might remember from previous articles are all considered conservative forces. Talking about internal forces, we can apply the so called conservation of energy theorem, which tells us that the total (mechanical) energy of a system gets conserved over time.

## RESOURCES:

### References

1. https://www.britannica.com/science/internal-energy
2. http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/inteng.html
3. https://physics.info/work/
4. https://www.physicsclassroom.com/class/energy/Lesson-2/Internal-vs-External-Forces

### Images

1. http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/inteng.html

## Final words | Next up

This is actually it for today's post! I'm not quite sure about next time. It's possible that we will get into the next topic of momentum, but maybe I will first get into exercises around the whole conservation of energy stuff :)

See ya!

Keep on drifting!

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