KidBridges

ENTRY 2

After we read

about tension and compression, we got our own ideas. We didn't just copy what it said!

Here's what we did:

Sheryl and I leaned towards each other and pressed the palms of our hands together. Our arms were in compression

. They were pushing each other.

Then we grabbed each other's hands and leaned backwards. That time, our arms were in tension

we were pulling each other. We asked the whole class

to get up and try it too so they could feel what tension and compression felt like in their bodies.

Next we had kids try to push each other over. But some kids who knew about martial arts messed things up. While Jose was pushing Lucy as hard as he could, Jose just stepped back and Lucy almost fell

. Pretty soon everyone fell on the floor and the whole class made so much noise that Ms. T. had to say "OK, GET UP!" about 5 times to get us to stop.

Ms. T. explained that the reason that we didn't fall over when we did this at first was that the opposing forces were in balance, or in equilibrium

. When one of us let go, we stopped being in equilibrium and someone fell down. I asked if the bridge would fall down too if there was no balance or equilibrium

. Ms T. said yes, but she said it was a little more complicated than that.

So, she told us to look on the Web, and when we did we found a diagram

of how the forces on a bridge balance. We drew it on the board so everyone could see it. On the Web we also found that a bridge has live load

and dead load

. Dead load

is the bridge itself, including the road, and the trusses and everything like that. Live load

is the people and the cars and the stuff that moves across the bridge.

Can you think of examples of live load and dead load in this classroom?

Ms. T.

When we go on the bridge walk, we hope that this will all make a lot more sense.

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