Editing Tyndall's Bar Breaker (section)

===Full Explanation===
All metals, as well as most other solid materials, can expand or contract as they are heated or cooled, respectively. The amount that they expand or contract is dependent on the type of metal, and is known as the ''Elastic Modulus'', or ''Young's Modulus'', of the material. Metals tend to have a very high elastic modulus, which means that they expand or contract in very small amounts as they are heated or cooled. Even still, they can still expand when heated and contract when cooled, and this tiny change can have dramatic effects.

{| class="wikitable" style="color:black; background-color:#ddd; text-align: left; margin-right: auto"
|+ Elastic Modulus Equations:
| '''E''' = ('''F'''*'''L'''<sub>i</sub>) / ('''A'''*'''ΔL''')
| '''U''' = ('''E'''*'''A'''*'''ΔL'''<sup>2</sup>) / (2*'''L'''<sub>i</sub>)
|-
| '''E''': Elastic Modulus || '''U''': Energy
|-
| '''F''': Force (Tension)|| '''A''': Area of Force Applied
|-
| '''L'''<sub>i</sub>: Initial Length|| '''ΔL''': Change in Length
|}

When the iron bar is being heated, there is energy being added into the system. By looking at the second equation, we can use the amount of heat energy being added to calculate how much the length of the iron bar is going to change, '''ΔL'''. It is important to note that the area that the force will be applied on, '''A''', is actually very small. The metal ring that the iron ingot sits inside has a thin metal edge in the center, which is much smaller than the width of the ring. Even still, because the elastic modulus is very high, '''ΔL''' will only be a small change. When the heat is taken off, the iron bar starts to contract, and the tension force in the bar starts to get bigger. This is because, although the change in the length and the area that the force is applied on are both small numbers, the elastic modulus is still a very large number, and so the force needs to be big. As the bar contracts more, the force increases over time, until finally it becomes too much on the iron ingot and breaks it!

When we are looking at the equation, we can see the force and the area applied as being equal to pressure, or '''P'''='''F'''/'''A'''. This helps us understand why we use a small area inside the ring instead of a larger area; by using a smaller area, we can use less force to generate a greater amount of pressure on the iron ingot. Since iron is brittle, or breaks under pressure rather than bends, this means our ingot has to break once the iron bar contracts enough!