Low Temperature Physics: Liquid Nitrogen.
The air we breath is about 78% nitrogen. Typically this is a gas but when brought down to an extremely cold temperature nitrogen becomes a liquid. Not only is liquid nitrogen fun to play with, but it gives you an opportunity to begin to explore low-temperature physics.
What You Need
- safety goggles
- tongs and thermal mitt
- dewar (specifically designed to contain liquid nitrogen)
- sample of liquid nitrogen in a secure container
- plastic beaker
- table or other surface that will not be harmed by very cold temperatures
- Pyrex bowl large enough to hold a small quantity of liquid nitrogen and immerse the other objects listed here
- 12 inches (approximately) of lead tin or other solder wire
- 20 g hooked mass
- metal tube with one end open and the other sealed
- medicine bottle with easy snap on/snap off lid or a 35mm film canister
- cork that loosely fits into the open end of the metal tube
- Liquid nitrogen must be handled safely. This means it must be stored in a specially designed container called a dewar, which is intended for this purpose. Do not put liquid nitrogen in a typical lunchbox thermos, which should never be used for liquid nitrogen.
- Liquid nitrogen is so cold, it can freeze human skin in a very short time. For all these activities, all participants should wear safety goggles and avoid any sustained contact with skin. Be especially carefully to avoid splashing liquid nitrogen, which could get trapped under clothing and cause freezing. Also, remember, objects that have been immersed in liquid nitrogen have themselves been brought to a very low temperature and should be handled appropriately.
Splitting a banana
- Carefully pour some liquid nitrogen into the Pyrex bowl.
- Using the tongs and thermal mitt, immerse the banana into the liquid nitrogen for about 15–30 seconds. Initial bubbling and vaporization diminish as the banana approaches equilibrium with the liquid nitrogen, as shown in Figure 92-1.
- Remove the banana and place it on the table.
- Take the hammer and strike the banana, as shown in Figures 92-2 and 92-3. (For contrast, you can strike an unchilled banana either before or after, showing the effect of the much-more-brittle frozen version.)
- Using the same bowl as the previous experiment, immerse some fresh flowers in the liquid nitrogen.
- Drop the bouquet on the floor or strike them on the table.
- Form the piece of solder into a coil roughly ¾ inch (1–2 centimeters) in diameter.
- Notice the lack of stiffness in the spring.
- Immerse the spring in the liquid nitrogen for roughly 15–30 seconds.
- Hang a 20 g (or so) hooked mass from the frozen spring and compare its stiffness with that of the room-temperature version.
Balloon—filled with air
- Blow up the balloon and tie a knot in the open end.
- Immerse the balloon in the liquid nitrogen.
- Observe what happens as the balloon is cooled.
- Remove the balloon from the liquid nitrogen and again observe what happens.