imported>Stwikiadmin: /* Full Explanation */

2016-07-15T18:08:20Z

Full Explanation

← Older revision		Revision as of 18:08, 15 July 2016
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	\|+ Elastic Modulus Equations:		\|+ Elastic Modulus Equations:
	\| '''E''' = ('''F''''''L'''<sub>i</sub>) / ('''A''''''ΔL''')		\| '''E''' = ('''F''''''L'''<sub>i</sub>) / ('''A''''''ΔL''')
	\| '''U''' = ('''E''''''A''''''ΔL'''<sup>2</sup>) / (2*'''L'''<sub>i</sub>		\| '''U''' = ('''E''''''A''''''ΔL'''<sup>2</sup>) / (2*'''L'''<sub>i</sub>)
	\|-		\|-
	\| '''E''': Elastic Modulus \|\| '''U''': Energy		\| '''E''': Elastic Modulus \|\| '''U''': Energy

imported>Stwikiadmin: Created page with "{| class="wikitable" style="color:black; background-color:#ddd; margin-left: auto; float:right" | Physics, Chemistry: | Properties of Metals |- | Grade Range: | [[Element..."

2016-07-15T17:56:04Z

Created page with "{| class="wikitable" style="color:black; background-color:#ddd; margin-left: auto; float:right" | Physics, Chemistry: | Properties of Metals |- | Grade Range: | [[Element..."

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{| class="wikitable" style="color:black; background-color:#ddd; margin-left: auto; float:right"
| [[Physics]], [[Chemistry]]:
| Properties of Metals
|-
| Grade Range:
| [[Elementary School]], [[Middle School]], [[High School]]
|-
| Format:
| [[Stage]]
|}

This demonstration takes time to work, but when it happens it will take everyone (sometimes even the presenter) by surprise! Be sure to follow all safety precautions with this demonstration, and to not let any students near it until it is fully cooled down.

== Materials ==

* Blowtorch
* Bar Breaker U-Bar
* Iron Ingots
* Test Tube Stand with Clamp Holder

== Safety Precautions ==

Please read the Fire Safety section of the [[Demonstration Safety]] page before performing this demonstration.

This demonstration requires: safety goggles or glasses, heat gloves, small blast shield.

== Demonstration ==

# Set up the stand and put the U-bar in the clamp holder. Put an iron ingot through the three holes in the U-bar, and tighten the nut on the rod as much as you can.
# Put on the safety gear and start heating the middle of the rod with the blow torch. As you heat it, continue to tighten the nut as you are able. Be sure to keep the blowtorch on one spot, and heat it until it starts to glow red. Once it is, make sure the nut is as tight as you can make it before turning off the blowtorch.
# Put the small blast shield in front of the setup, and switch over to a second demonstration. In 5-10 minutes, there will be a loud "PING!", and the iron ingot will be broken! Show the audience the broken ingot and ask them why it broke. What caused it to break?

== Why This Works ==

===Short Explanation===
Metals are very useful for a large number of reasons. They are strong, are good conductors, and have high melting points, which makes them ideal for building things. Although metals have a high melting point, they will still expand and contract in very small amounts as they heat up or cool down. The amount of force that two metals apply on each other can change due to how much they expand or contract, and it is the reason why the iron ingot broke.

As the iron bar was heated, it started to expand bit by bit, which is why we started tightening the nut for the bar. After heating it up until it was red hot, it had expanded so much that the nut could make a few full turns, meaning that the bar had expanded close to half an inch. After turning off the heat, the bar started contracting, and in doing so it started to pull harder on the iron ingot. Iron is a very strong metal, but it can be ''brittle'', meaning that it will break if hit with a high force instead of bending to absorb it. The iron ingot is absorbing more and more force as the bar continues to contract, until finally it cannot take anymore and breaks!

===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'''i) / ('''A'''*'''ΔL''')
| '''U''' = ('''E'''*'''A'''*'''ΔL'''2) / (2*'''L'''i
|-
| '''E''': Elastic Modulus || '''U''': Energy
|-
| '''F''': Force (Tension)|| '''A''': Area of Force Applied
|-
| '''L'''i: 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!

== Additional Information ==

* This demonstration pairs well with the [[Bi-Metallic Strip]], as they both show the contraction and expansion of metals.
* This demonstration is a part of the [[Pressure Show]].

Tyndall's Bar Breaker - Revision history

imported>Stwikiadmin: /* Full Explanation */

imported>Stwikiadmin: Created page with "{| class="wikitable" style="color:black; background-color:#ddd; margin-left: auto; float:right" | Physics, Chemistry: | Properties of Metals |- | Grade Range: | [[Element..."