Home >> Science & Nature >> Science

Will a Glass Bottle Break if You Make a Vacuum Inside It?

Although most kinds of glass are brittle, it can withstand very high pressures. A glass bottle with a vacuum inside it has a very modest pressure acting on its outside, so the bottle will not break. Many objects you encounter in everyday life, including thermos bottles, light bulbs and fluorescent tubes, are examples of glass bottles that contain a vacuum and can last many years without breaking.

Vacuum Pressure
- An empty, open bottle has air pressure acting on both the inside and the outside; these forces balance, so no net pressure acts on the bottle. When you pump the air out of the bottle to create a vacuum, the inside pressure drops to nearly zero, while the outside remains at 14.7 psi at sea level. No matter how much air you pump out of the bottle, the outside pressure never exceeds 14.7 psi. This is a relatively small pressure; auto tires, for example, run about 30 to 40 pounds per square inch, and water in a garden hose is between 30 and 50 psi.
Glass
- The term "glass" generally refers to silica mixed with alkaline materials, producing a clear or semi-clear material; however, glass makers produce many varieties for windows, lenses and mirrors, fiber optics and other applications. Engineers express the ultimate strength of glass as the "modulus of rupture"-- the pressure required to break it. Common soda lime glass has an MOR of about 5,000 psi and tempered glass yields at about 36,000 psi. Even the weakest types of glass easily hold up to the pressures needed to contain a vacuum.
Light Bulb
- A traditional incandescent light bulb is has a thin glass envelope that contains a vacuum. The absence of air prevents oxidation in the bulb's metal filament and helps it heat extremely rapidly, producing light. The light bulb's glass holds a vacuum almost indefinitely with careful handling.
Coffee Thermos
- A coffee thermos is called a "dewar flask" and is a double-walled glass container coated with a reflective silvery material. The glass holds a vacuum between its two inner walls, acting as an excellent insulator and keeping the temperature of the bottle's contents constant for hours, whether hot or cold. A well-made thermos can function for decades with careful use, as the glass holds the vacuum easily.
Vacuum Tube
- Vacuum tubes are electronic devices first developed in the early 20th century. Although transistors replaced tubes in the 1960s for many uses, they continue to have specialty applications in professional audio, radio broadcasting and high-voltage equipment. A vacuum tube is very similar in construction to a light bulb; the difference lies in the number of metal parts inside the glass envelope. As with light bulbs and dewar flasks, tubes can hold their vacuum for many years.

Science