Archive for March, 2009

Measuring the speed of light… the HARD way.

Okay, so if you’re a nut about physics, this is one I can sketch out fo you, but you’ll need to fill in the gaps on your own.  If you want an easier method, check out this post here.

You can recreate Galileo’s mountain-top experiment by arming yourself and a friend with identical digital watches and flashlights.  At a specified time, one of you flashes the light, and the other records the time when the flash is seen. The trouble with this is at unless you’re on different planets, you’re going to have a hard time seeing a less-than-instantaneous result.

You can modify this experiment so that you set up a mirror (instead of a friend) far away, and bounce a beam of light off the mirror and record the mound of time it takes for the light to travel the set distance.  And instead of using your eyeball to record “when” the flash of light returns, you can use a strip of film on a spinning wheel. A further step is to split the initial beam in two, and have one beam take a longer path to return home, and record the time difference on film (which you can back-calculate to get the time difference).

The first successful speed of light measurements were made by a Danish astronomer using an eclipse of Jupiter and Io.

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Freeze Swap

Fill a plastic container (such as a water bottle) about one-third full of water. Add one-third oil (so the bottle is now two-thirds full) and cap the bottle. Shake it up and see if you can get the two to mix. (If you add blue dye to the water beforehand, it makes this experiment easier to view.) Which is on top, the water or the oil? Stick the bottle in the freezer overnight (stand it upright and remove the cap first). Now which is floating on top?  What else can you test out?

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Making indoor rain clouds…

Chemistry Experiment: Indoor Rain Clouds Making indoor rain clouds demonstrates the idea of temperature, the measure of how hot or cold something is. Take two clear glasses that fit snugly together when stacked. (Cylindrical glasses with straight sides work well.) Fill one glass half-full with ice water and the other half-full with very hot water (definitely an adult job – and take care not to shatter the glass with the hot water!). Be sure to leave enough air space for the clouds to form in the hot glass. Place the cold glass directly on top of the hot glass and wait several minutes. If the seal holds between the glasses, a rain cloud will form just below the bottom of the cold glass, and it actually rains inside the glass! (You can use a damp towel around the rim to help make a better seal if needed.)

You can turn this into a science fair project by testing the effects of water temperature… what is the ideal water temperature to really ‘make it rain’?

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