Basic Thermodynamics ~ J. Pohl © (C2250) | (9/14) ~ (Polaris Model) |

An elephant and her mahut can weigh a teak log. When shown a piece of chalk and the log to lift, the elephant knows what to do. With its trunk and tusks the elephant lifts the log slowly, carefully to a balanced, level position, pauses, then puts the log down. The mahut marks the balance point of the log as his helper climbs onto one end.

Again the mahut shows the chalk, and the elephant lifts and balances the log with the helper standing on one end and grasping the elephant's ear for balance. Once the elephant holds the log level, the mahut measures two distances (see sketch), the elephant puts the log down and the mahut chalks the weight of the log on it. A sketch is provided.

**Calculate** the weight of the log.

♦ For the second lift, we sum the moments of the weight of the helper and the weight of the log about the point at which the elephant holds the log. We take counter-clockwise moments as positive.

0 = ΣM

0 = r_{helper} x 32 kg - r_{log} x mass_{log}

0 = 1m x 32 kg (9.81 m/s^{2}) - 0.15 m (9.81 m/s^{2}) mass_{log}

Therefore,
mass_{log} = (1 m/0.15 m) 32 kg = 213 kg

And that's how the elephant does it!

An elephant and her mahut can weigh a teak log. The mahut shows the elephant a piece of chalk then points to a teak log; the elephant knows what to do. With its trunk and tusks the elephant lifts the log slowly and carefully to a balanced, level position, pauses, then puts the log down. The mahut marks the balance point of the log as his helper climbs onto one end. The elephant is shown the chalk again. It lifts and balances the log a second time with the helper standing on one end, grasping the elephant's ear for balance. The mahut uses this information to estimate the weight of the log.

Premise presently unwritted!