Equipment: Two 12" rulers, a small (~2L) dewar of liquid nitrogen, safety goggles and safety gloves.

What it does: One ruler is cooled to liquid nitrogen temperature and one is left at room temperature. The two rulers are compared to show that the cooled ruler has contracted.

Concepts Demonstrated: Thermal expansion/contraction.

Classroom assembly:

1. Place both rulers on the overhead projector so they touch with the cm scales aligned side-by-side. Note that the rulings line up exactly."
2. Place one ruler in the dewar of liquid nitrogen with the 0cm end down. WEAR APPROPRIATE SAFETY GEAR. Note that the entire ruler will not be submerged.
3. Wait until the ruler is fully cooled to liquid nitrogen temperature.
4. Remove the cooled ruler from the liquid nitrogen.
5. Place both rulers on the overhead projector and align them as before. Note that the rulings no longer line up. The cooled ruler is now shorter.

Note:

• BE QUICK. The cooled ruler heats up quickly.
• Occasionally the cooled ruler will curl or bend. If this happens, hold the ruler flat on the overhead.

Cautions:

• Liquid nitrogen can cause severe burns and blindness. Use with caution.
• This demonstration requires advanced practice. Aligning the rulers in time is difficult.

Setup Time: Short.

Difficulty: Straightforward.

Visibility: High. This demonstration can be shown on the overhead projector and is appropriate for large lecture halls.

Related demonstrations:

References:

Original Construction: Assembled from existing equipment.