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Jamming Rice
Find out how to pick up a jar of rice without touching the jar, and what it has to do with holes in the road.
What you need
| A jar |
| A knife about as long as the jar |
| Slightly more rice that will fit in the jar - Basmati seems to work best. |
What to Do
Fill the jar with rice
Put the knife into the jar and wiggle it gently for a while take the knife out and put it in again wiggle it some more.
You will have to keep topping up the jar with rice, and it will take a few minutes.
at some point you will find something strange happens when you take the knife out.
What may Happen
As you wobble the knife you will notice that the level of the rice drops, and it slowly gets harder to move the knife.
Eventually when you try and take the knife out it stays stuck in the jar.
What is going on?
When you pour rice into
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The rice grains are not well organised so there is plenty of space between the grains. | This means that when you put the knife into the rice there is space for the grains to move out of the way. |
When you shake the grains gently with the knife the grains fall down into the gaps between the other grains filling up most of the spaces.
If you look closely in the jar you will notice that the grains tend to line up, this is because they take up less space this way.
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The better packed grains mean that you have to add more rice to fill the jar (pink grains) | There is no longer any space for the grains to rearrange themselves, so the only way they can make space is to distort and break. |
Because there is very little space for the grains to move into when you push the knife into them, so they have to bend and distort to allow the knife to get in - just like a piece od wood would have to. This takes a lot of force to do so the rice will push backand grip the knife allowing you to pick up the jar with the knife.
What has this got to do with holes in the road?
When the road is dug up it is normally mended so the repair is flat, but after a couple of years it normally turns into a dent. This is because the stones that
were used to fill the hole are vibrated slightly by traffic going over the top which means that they pack better, take up space and create a dent.
Written by Dave Ansell
| Listen to this as part of the show: 10th Jun 2007 - The Naked Scientists Q&A Show |
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