Swinging and swaying! Use inertia to stabilize a skyscraper you build.
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| skycraper earth-quake resistent |
collect
POPSICLE STICKS
TAPE
PAPER CLIPS
PLAY DOUGH
RUBBER BAND
STRING
HOT GLUE GUN
Two of nature’s strongest natural forces – wind and earthquakes – can have a great effect on our tallest man made structures, skyscrapers.
At high altitudes (at the tops of our high skyscrapers), wind can reach very high speeds. Wind speed increases with altitude. The wind moves slower closer to the ground because of friction. On the ground, air molecules bump into things like trees, rough terrain, buildings, etc which partially block the flow of the wind. The higher you rise in Earth’s atmosphere the less obstacles in the way of the wind causing wind speed to increase. High speed winds can push on a building and cause it to sway back and forth.
Have you ever felt the ground shake when a large trucks drives by on a bumpy road? When the truck passes by, it is sending vibrations out into street and down into the dirt and after a chain reaction of vibrations, the ground underneath your feet starts to vibrate. These are pretty small vibrations, so they are nothing to worry about, but there are times that the earth shakes more violently, during an earthquake!
The earth is very hot at its core, so hot in fact that deep in the Earth there are not solid rocks, but molten liquid rocks. On top of the liquid floats the crust of the Earth, the hard layers of rock where we live. This hard layer is broken up into a number of pieces called tectonic plates. The joints where these plates come together are called plate boundaries. The big tectonic plates grind and slide past one another sometimes, which causes huge vibrations, that we call earthquakes.
If you build a tower of blocks on the floor and then jump up and down really hard next to it, you know that vibrations can be trouble for tall buildings. If you blow hard enough you might even be able to blow the blocks over. Skyscrapers are in danger of falling over unless engineers design them correctly to withstand the vibrations from earthquakes and wind gusts.
One way that engineers try to offset the effects of the vibrating earth and blowing wind is to install mass dampers. In its simplest form a mass damper is a large heavy ball hanging by a string at the top of a large building. How does it work? When an earthquake shakes a building it tends to start the building swaying back and forth. The ball however does not want to start swaying, because it has inertia. Inertia is the property of matter that makes it hard to start or stop moving. Grab a hold of something heavy and try to shake it. When is it most difficult? When you try to change the weights direction! The bigger the object the harder it is to get moving. So how does this apply to the skyscraper?
Imagine the skyscraper is swaying to the right. As it starts to sway the ball is applying a force (a pull) to the left, but eventually, it will start to move to the right too, just like the weight responded when you changed its direction. When the building starts to sway back to the left, the ball is moving to the right still and again will apply a force in the opposite direction that the building is moving. This tends to keep the building more stable.
experiment
Build a sky scrapper at least 1.5 feet tall, using your supplies.
Use Popsicle sticks to build a frame that can attach to the top of your sky scraper. This frame will hold up your mass damper (ball of play dough), so it needs to be strong.
Clump your play dough into a ball around the paper clip so there is a hook sticking out of the top that you can attach a string or rubber band to.
Secure your frame and hanging ball on the top of your sky scraper.
Shake shake shake!
reflect
To see if the mass damper is working, try unhooking it and just setting the ball on the top of your sky scraper.
Is the building swaying more or less than when it was installed?
Does the speed at which you shake affect how well the mass damper works?
What happens when you make the string longer or shorter?
What about the weight of the ball, does that affect how well the mass damper works?
Original Post here http://curiositymachine.org/node/47
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