Bag of Lead Shot

Dropping bag containing lead turns gravitational potential energy to heat.

What it shows: 

A demonstration of the conversion of gravitational potential energy to heat energy. A bag of lead shot, repeatedly dropped to the ground, will heat up.

How it works: 

Lead has a sufficiently low specific heat capacity (128 J/kg/K) that a 5kg bag dropped five times from a height of 1.0m onto a rigid floor should increase in temperature by about 2K. The shot is contained in a bank deposit bag with reinforced stitching; its temperature is read before and after the drops with an Omega® temperature probe (See The Supercooling of Water).

Setting it up: 

Make sure the probe is placed at the center of the shot and given time to reach equilibrium. Take the final temperature immediately after the final drop. Keep a meter rule handy for height measurements. Before handing this demo to the lecturer, check the seams of the bag.


You do get a temperature rise, but there are a lot of losses. We have yet to find a bag capable of taking the punishment of this demo, hence the underlining in Setting it Up.