by Candi » Fri Jan 23, 2009 2:45 pm
Here are some fun experiments we did with water....
These were found in Bathtub Science by Shar Levine and Leslie Johnstone.
Lil' Hydroplane--
1. On a 2 inch square piece of foil, draw a small, simple house shape with a small, oblong "door" shape in the center of the front of the piece of aluminum foil. Cut along the outline of the house, cutting out the door shape. Discard the leftover foil. This is your miniature boat; the cutout door is the boat's "tank".
2. Fill a bowl (or tub) with water and place the boat in the water with its front end facing away from you and "tank" (door) facing towards you.
3. Using a toothpick, drop a small drop of dishwashing liquid (this is your "fuel") into the "tank" (door).
What happened:
Your boat jetted across the water. When the soap was placed into the "tank", the molecules that make up soap and the molecules that make up water spread out on the surface of the water, and they had only one direction they could move in. They moved out through the gap at the back of the boat. Just like the jet engines that move real hydroplanes by shooting out hot gases, the water shooting out the back of your boat drove it forward. The boat won't keep working forever. Eventually, the surface of the water gets too full of dish soap and your boat stops moving. But fill the bowl (or tub) with fresh water and it will work again as good as new.
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Water Glue--
1. Fill one glass with water and place a second glass on a flat, stable surface. Pour water from the first glass into the second until the second glass is filled to the very top.
2. Add one penny at a time to the glass of water by sliding the penny over the edge of the glass. Do not drop the penny into the water. How may pennies do you think you can put into the glass before the water spills over the edge?
3. Keep adding pennies one at a time. Each time you add a penny, look at the glass from the side. What does the water's surface look like when you look at it from this angle?
4. When the water begins to run down the outside of the glass, stop adding pennies. Dump out all the water and count the pennies. How may are in the glass?
5. Repeat step 1, only this time add a tablespoon of salt to the water in the first glass before you pour it into the second. Slide pennies over the edge again. How many pennies did you add before the water began to drip?
What happened:
When you added the first few pennies, the water did not drip over the edge of the glass. Instead, the water formed a shallow dome shape above the rim of the glass. This is because the molecules that water is made up of are attracted to each other more than they are attracted to the molecules that make up the air or the plastic glass. The parts that make up the top surface of the water form a film or "skin". This thin film or skin, lifts up to form a dome shape as each additional penny is added and the pennies "stick" to the water. When enough pennies are added, the film cannot hold all the water beneath, so it breaks and the water begins to drip down the side of the glass. When salt is added to the water, it makes the water less sticky. This means that fewer pennies can be added before the water drips over.
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Pop Bottle Hip Hop--
1. Place a coin over the top of a plastic bottle (a 2 liter bottle and quarter work well). Choose the coin that fits best over the bottle's opening and most tightly seals the bottle. Keep this coin handy for the experiment.
2. Place the empty bottle in the fridge for about an hour, so it is really cold.
3. Fill a bowl (or tub) with warm water. Remove the bottle from the fridge. Dip your hand into the water and add a few drops of water to the rim of the bottle. Place the coin on the wet rim. The water will form a seal between the coin and the rim of the bottle.
4. Hold the bottle in two hands and slowly lower it into the warm water. Make sure you keep the bottle level, so the coin doesn't fall off. Your coin should start dancing. If it doesn't, check the seal to make sure there is water between the coin and rim of the bottle.
What happened:
The water warmed the air in the bottle. When air is warmed up, its entropy increases and the molecules (tiny particles) that make up the air move faster and away from each other, to become more disordered. This made the air expand, or swell up. When the air in the bottle swelled up enough, it pushed up on the coin and some of the air escaped. The coin dropped back down and sealed the mouth of the bottle again. Then the air began to swell up some more, and each time the coin lifted and dropped back down, more of the air escaped.