Question

Which is heavier, wet or dry sand?

Asked by: Katherine Robertson

Answer

Which would you think is heavier? If wet sand is simply dry sand with water in it than clearly wet sand is heavier. But wait! We have to define our terms here. This is why this is such a good question! I am impressed that you should wonder about something so obvious!

When doing science one has to be very careful how they speak, or write. Your question sounds like one I used to trick my elders with when I was a child. 'Which,' I would ask, 'is heavier: A ton of bricks or a ton of feathers?' The unthinking adult would answer, to my delight, that the ton of bricks is heavier. I realize your question is not meant to be a trick but it does illustrate how careful one must be.

If you were to ask 'Which takes up more space, a pound of wet sand or a pound of dry sand?' then the answer would be that a pound of dry sand takes up more space since it takes more dry sand to equal a pound. But, you asked which is heavier. Before answering such a question one would have to ask how much space that sand is taking up. In other words you could have asked: Which is heavier, a bucket full of wet sand or a bucket full of dry sand? The answer to that question would be the bucket of wet sand since that bucket is full of sand and water.

At this point your question really gets good. Why? Because the next question would be something like this: How could the bucket of wet sand be heavier? After all, water is not a heavy (or dense) as sand and if the sand in the bucket has to make room for the water it would have to hold less sand and therefore the sand and water combination should weigh less than the sand alone!

Now, there is a good question! I can see why you, or anyone who is a thinking person, would think, logically, that if you have equal volumes of wet and dry sand the wet sand would weigh less. this would have to be true since the water takes up the space the sand would have taken if the water were not there and since water is less dense than sand the combination of water and sand to equal a volume of dry sand would have to weigh less.

There is just one thing: There are spaces between the sand, not big spaces but spaces nevertheless; spaces big enough for water to get into without moving any sand out of the way. In other words, you could take your bucket of dry sand and fill it with water and move not one single grain of sand out of the bucket. So equal volumes of wet and dry sand would not weigh the same; the wet sand would weigh more because it has more mass, the mass of the water in-between the sand and the mass of the sand itself. The dry sand has only the mass of the sand and the air between the grains of sand.

But, you can see how wonderfully this question shows how careful scientists must be when they ask a question. You know, the art of asking a question is a much more valuable skill than the ability to answer them. You are the better scientist for asking the question than I am for answering it! Keep asking questions!

Answered by: Tom Young, M.S., Science Teacher, Whitehouse High School, Texas

Search

Loading


Support Discovery Capsule - Anton's new project on Kickstarter.



Science Quote

'One thing I have learned in a long life: that all our science, measured against reality, is primitive and childlike - and yet it is the most precious thing we have.'

Albert Einstein
(1879-1955)
Science Sidebar | Science Education Articles
Cool Summer Science Projects

Why not make science a part of your family’s summer? Perhaps you can set aside one day a week for outdoor projects—maybe Mad Scientist Monday or Scientific Saturday? Here are a few ideas to help get you started. Continue reading ...

10 Ways to Keep Your Kids Interested In Science

Young children are natural scientists: they ask questions, pick up sticks and bugs outside, and are curious about the world around them. But as they get a bit older, many kids gradually lose their interest in science. They might see it as just another task at school, something that doesn't apply to their lives. Of course nothing could be further from the truth, so here are ten ways you can remind your kids that science is everywhere. Most of these are fun for adults, too! Continue reading ...

Top Selling

Here are our physics & astronomy bestsellers:
Deluxe Water Rocket Set
Magnetic Levitator - Classic
Scorpion, Ant, Wasp and Flower Bug
12 inch Galileo Thermometer
Revolving Multi-Color Fiberoptic Light
Solar Radiometer
Enviro Battery 4M Kit
Tin Can Robot 4M Kit
Wood Grain Newtons Cradle
Brush Robot 4M Kit

Sponsors

USC University of Southern California Dornsife College Physics and Astronomy Department McMaster University Physics and Astronomy Department