# The Naked Scientists Forum

### Author Topic: the properties of silly putty  (Read 4023 times)

#### paul.fr

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##### the properties of silly putty
« on: 02/06/2007 16:18:58 »
if you watch this video on youtube:
you will see a 50lb ball of silly putty dropped from height, it appears that when it hits the ground it stretches first the turns in to a solid and shatters.

Why the change in properties?
« Last Edit: 02/06/2007 16:34:11 by paul.fr »

#### DoctorBeaver

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##### the properties of silly putty
« Reply #1 on: 04/06/2007 16:55:49 »
Interesting question.

*waits for someone who knows the answer*

#### DoctorBeaver

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##### the properties of silly putty
« Reply #2 on: 04/06/2007 16:56:27 »
Actually, this may be better suited to the Chemistry forum

#### Karen W.

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##### the properties of silly putty
« Reply #3 on: 04/06/2007 16:59:54 »
IT shatters?? Weird!~ I better go see!

#### Karen W.

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##### the properties of silly putty
« Reply #4 on: 04/06/2007 17:03:09 »
That was interesting!

#### DrDick

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##### the properties of silly putty
« Reply #5 on: 04/06/2007 17:09:04 »
It's an example of non-Newtonian viscosity.  Newtonian viscosity is independent of shear or time - the viscosity stays constant.  Non-Newtonian viscosity is dependent on those things.

In this example, when the silly putty hits the ground, the viscosity increases sharply as it experiences the force upon hitting the ground.  At high viscosity, the material is no longer pliable, so it fractures instead deforming.

You can also see this happening when you mix cornstarch with a little bit of water.  If you press down on the cornstarch lightly, you can poke your finger through with little resistance (depending on the relative amounts of water and cornstarch).  If you press down hard, however, you find that it is very difficult to poke into the cornstarch.

You can even grab a glob of cornstarch and form it into a ball as long as you squeeze the ball as you're making it.  If you then let the ball rest in the palm of your hand, the ball will almost instantly liquefy and ooze off your hand.  Again, this will depend on the ratio of cornstarch to water, so play around with it.

Cornstarch and water is great fun to play with.

Dick

#### DoctorBeaver

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##### the properties of silly putty
« Reply #6 on: 04/06/2007 17:11:18 »
I'm going to have to try the cornstarch thing. Could make a good trick in my local!

#### Bored chemist

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##### the properties of silly putty
« Reply #7 on: 04/06/2007 19:47:08 »
More likely to make a mess in your local.
Fine, it's a non Newtonian fluid. That's just giving the behaviour a name. Another name for this property is dilatency (the opposite is thixotropy).

Why does it happen?
And by the way, kudos tho the people who actually did the experiment- who says that interesting physics costs billions? (Oh, while I remember, it's physics not chemistry- no chemical bonds are broken or made; no reaction takes place.)

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##### the properties of silly putty
« Reply #7 on: 04/06/2007 19:47:08 »