# Homework Help: What causes sand to get hotter then water?

1. Jan 5, 2005

### jjjsarnis

question: on a sunny day at the beach, the reason the sand gets hot and the water stays relatively cool is attributed to the fdiffernce in which property between water and sand?

is it specific heat or thermal conduvtivitiy??

our class and our teacher argued over this all class, thanks for your help

2. Jan 5, 2005

### Gokul43201

Staff Emeritus
Both.

The low specific heat ensures that something receiving a smaller heat flux gains a larger increase in temperature. The low conductivity (which is mostly due to the poor thermal contact between sand grains) ensures that the temperature gradient created can be large for a given rate of downward heat removal.

In other words :

First the surface layers of water and sand get heated directly by the sunlight. If none of this heat is conducted away, the sand will reach a higher temperature than water because of the lower specific heat. However, the heat does get conducted away. But again, since it is conducted away more slowly by the sand, than by the water, the surface of the sand stays hotter.

With calculus (differential equations), this can be modeled reasonably easily.

3. Jan 5, 2005

### Andrew Mason

I agree with the low specific heat point. To undergo a temperature increase of one degree, the sand requires much less heat than water. So the same amount of heat/unit area incident upon sand and upon water will increase the temperature of the sand much more.

But I am not sure about the thermal conductivity. Its thermal conductivity is the same as sawdust and I don't think sawdust would feel as hot as sand if you set them out in the sun.

AM