Experiment 2: Prince Rupert's Tear Drop

Experiment Title: Prince Rupert’s Teardrop

Experiment Description (should be at least more than 200 words)

Prince Rupert’s teardrop is a weirdly shaped teardrop of glass named after Prince Rupert of the Rhine, who showed it off in England in 1660. It’s created by melting glass over cold water and letting the molten drop bead off into the water. The resulting teardrop has marveled scientists for hundreds of years. It has a bulbous head so strong that it can withstand forces of up to 287,900 newtons and a wiry tail so fragile that any fracture makes the drop explode into a fine powder of glass. This happens because the surface of each drop experiences highly compressive forces while the interior experiences incredibly high tension forces, causing the drop to be in a state of unstable equilibrium. This unstable equilibrium can be easily disrupted by breaking the tail. These tension forces are caused by the way the drop forms, when the blob of molten glass makes contact with water the exterior rapidly cools and shrinks, while the interior is still molten. The outside fully cools and is set into place and then the inside cools but cannot shrink as the outside is already set. This interior shrinking causes the interior tension. The surface compression layer is only about 10% the diameter of the head, and the only way to break the drop is to create a crack that enters the interior tension zone. The tail is the best way to introduce a crack is in the tail because it is part of the tension zone, and even the tiniest disturbance will shatter the whole drop. When the end of the tail is cracked the disturbance races from the tip to the head at speeds exceeding 4,000 mph. Such a marvel of physics only requires glass of some form, a very high heat source, and a bucket of cold water.

Notes:

Glass melts between 2,552 degrees and 2,912 degrees Fahrenheit
Head so strong it can withstand gunshots
Tail so weak that the tiniest snap disintegrates the whole thing
made by dropping red hot blobs of molten glass into water
the surface of each drop experiences highly compressive stresses
- while the interior experiences high tension forces
- the drop is in a state of unstable equilibrium
  - Which can be easily disrupted by breaking the tail
Stresses caused by rapid heating and cooling in short time
- The outside cools while the inside is still hot
  - The outside shrinks and fully cools
  - Then the inside cools but cannot shrink as the outside is already set
    - Causing the interior tension
Heads have a much higher surface compressive stress of up to 700 megapascals
- This surface compression layer is only about 10% of the diameter of the head
The only way to break the drop is to create a crack that enters the interior tension zone
- The interior is under so much stress that any crack will shatter it all
- The tail is the best way to break it since a disturbance in this location allows cracks to enter the tension zone
When cracked the cracks race from the tip to the head of a Prince Rupert’s drop at speeds in excess of 4,000 mph