Uploaded June 2013 | Updated September 2026, 3 hours ago

---

This is one of my all time favourite experiments!
You start by creating a hook in the end of a short length of soda glass (look for the colour of the flame!) A mass is then attached and the glass is heated until it starts to stretch (stop heating as soon as it has fallen about 10cm).
Masses can now be attached to the glass fibre to find the breaking force and the diameter measured at the break point using a micrometer. Once these are known, the breaking stress can be calculated using the formula:

Stress = Force/Area

My values were:

Max mass = 400g (force = 3.92N)
Diameter = 0.21 mm

Please note:
The glass in this experiment gets extremely hot and stays hot for a long time. Please take care when handling.
The ends of the glass are extremely sharp and fragments can be scattered widely when it breaks. Make sure you wear safety goggles at all times.

Finally, I would love to see some videos showing the longest fibre you can create - if you try this out, please post a video response to my video!