# Ask a Physicist Answers

## Is it true that pressure exerted by a human foot is more than than exerted by that of an elephant?

The pressures exerted by an elephant or a human will depend on their weights and the areas of their feet. Also the elephant will be standing on four feet while the human will be standing on two. Let’s look at some typical values. There is a lot of information about elephants in the Elephant Information Repository at http://elephant.elehost.com/. Depending on the type of elephant, its mass can vary from 2000 to 7000 kg, take 4000 kg as an average. On the anatomy page of the Elephant Information Repository they mention that an elephant’s foot is circular with a circumference of about ½ its shoulder height. Shoulder height varies from 2 to 4 m. Taking 3 m as an average gives the area of one foot as about 0.18 m2. With these values the pressure exerted by an elephant is about 54,000 Pa (pascal = N/m2).

I took a typical mass for a man to be 85 kg (about 185 lb) and, from measuring my own foot got the area of one foot as 0.03 m2. This leads to a pressure of 14,000 Pa much less than an elephant.

What about a very heavy man and a very light elephant. Take the elephant’s mass to be 2000 kg and the man’s to be 140 kg (about 300 lb). Assuming the foot areas to be unchanged, the elephant exerts a pressure of 27,000 Pa and the man exerts a pressure of 23,000 Pa, still less than the elephant even for this very extreme case.

Answered By: Kenneth S. Mendelson, Marquette University