Re: Which heats up faster, sand or saltwater?

Renae, that is a very neat and tricky question. It is not nearly as simple as it sounds, and it would 
be very easy to do experiments and come up with quite different answers.

If you go to the beach on a hot sunny day, you can burn your feet on the sand, but you cool them 
down again when you put them in the ocean. That seems to mean that sand heats up quicker than 
water. But if you take a bottle of drink and a bucket with you, and you put the bottle in the bucket, 
it will keep cooler if you bury it in sand than if you cover it with seawater! That seems to mean that 
the seawater heats up quicker than the sand!

Here is how scientists see the difference:
(1) seawater has a higher HEAT CAPACITY than sand. It takes more heat energy to make a kilogram 
of seawater 1 degree hotter than it takes to make a kilogram of sand 1 degree hotter.

(2) seawater is a better heat CONDUCTOR than sand. A warm patch of water will share its warmth 
with nearby cold water much quicker and more efficiently than a warm patch of sand. The fact that 
water can move in currents and transfer its heat by CONVECTION makes heat transfer in water 
even more rapid and efficient. Sand does not transfer heat at all well. If you dig in the hot sand 
that burns your feet on the beach, you will find that you only have to go down a few inches before 
it is quite cool. (At the beach this might be because the deeper sand is wet, but you will find even 
in the desert that the sand a few inches down is much cooler, as long as you are not in a 
geothermal area).

So when the sun shines on sand, it heats up very quickly on the surface because the sun's energy 
only has to be shared within the surface layer, and because it takes only a small amount of energy 
to make sand 1 degree hotter. When the sun shines on seawater, it heats up slowly because it 
takes more energy to make seawater 1 degree hotter, but mostly because the heat has to be 
shared around the whole of the ocean down to a few metres depth!

But when the sun shines on your bucket, the heat that goes into the seawater gets shared around 
quite quickly, and will warm up your drink as well. If the bucket contains sand instead, then the 
top surface will get very hot, but the transfer of heat to the lower levels of sand will be very slow, 
and that deeper sand and your drink will stay cool!