This is scientific American 60 second science.

I'm Christopher in Tagata.

Got a minute?

Ever run along wet sand and it hardens up almost like concrete under your feet,

but pick up that same sand and it drizzles through your

fingers.

So that's the essence of why granular materials are interesting.

Yale physicist Abe Clark.

Sometimes they can behave like solids.

And other times like fluids.

Understanding the transitions between liquid and solid,

that's really non-trivial.

Grains of sand or otherwise are Clark's specialty.

He and his colleagues recently investigated

how a bucket of beads responds

when another object falls into him.

It's analogous to dropping a stone on sand

and then observing how the stone's force transfers to the grains.

The top grain is contacted by the intruder, and then it tells a friend, and so forth, and it moves

along a little chain. So what this looks it moves along a little chain.

So what this looks like is basically little lightning bolts of force

shooting off the intruder.

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