Demonstrations

 MechanicsFluidsHeatWaves & SoundLightElectricity & MagnetismModern PhysicsChemical Reactions

### ## Fluids 19. Air MassFill two balloons with air and attach them to the ends of a meter stick. Balance the meterstick on a narrow edge. Use a pin to release the air from one of the balloons. The meter stick should now tilt toward the balloon that is still filled with air. Ask students to explain why. (TOC)(TOC)20. Hero's FountainTwo two-liter bottles are connected with a clear plastic tubing running between them. The column of water is balanced against a column of air and water. The water seems to rise higher than the surface of its resevoir.(TOC)(TOC)21. Atmospheric Pressure I

 Vaporize a few drops of water in a beverage can using a hotplate. With tongs, quickly invert the can and plunge it intoa large beaker filled with cool water. The loss of internal pressure, due to the rapid condensation of the water vapor, will allow atmospheric pressure to implode the beverage can. (TOC)
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22. Atmospheric Pressure II

 A one gallon can is evacuated with a pump and is subsequently crushed by the atmospheric pressure. Alternatively, the can can be crushed by vaporizing a small amount of water and capping the can. Upon cooling, the vapor returns to liquid and loses pressure.(TOC)
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 A large flask with a few drops worth of water heated to steam is fitted with a balloon. As the flask cools down, atmospheric pressure pushes the balloon down into the flask.(TOC)
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24. Cartesian Diver
 A medicine dropper is partially filled with water so that it is just buoyant in a water filled whiskey bottle. Squeezing the broad sides of the bottle increases the pressure in the bottle which is translated to the just buoyant medicine dropper. The reduced volume of the dropper allows it to sink.(TOC)
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25. Spherical Oil Drop
 A layered mixture of water and alcohol has a region of density equal to that of vegetable oil. As oil is added to the mixture, it sinks to a stable depth and collects into a large spherical drop under the action of the oil's surface tension.(TOC)
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26. Floating in a Jet Stream
 A nozzle projecting a jet of high velocity air can suspend various objects such as ping-pong balls, etc. The viscous force of air balance the weight and the low pressure in the jet keeps the object trapped in the air-stream.(TOC)
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## Heat

27. Drinking Bird
 This commercially available toy demonstrates the conversion of thermal energy to mechanical energy. As it dips its beak into a glass of water evaporative cooling induces the rise of volatile liquid from his tail toward his head. As he dunks, the liquid returns to his tail, the bird rises, and the process repeats.(TOC)
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28. Thermal Expansion
 A laminated bar made from two different metals fastened in a wooden handleis placed over a flame. The different thermal expansion rates cause the bar to bend.(TOC)
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29. Thermal Energy of Food
 A dramatic illustration of the caloric content of food can be conducted by burning a dry-roasted peanut on the end of a long pin. The peanut will burn for about one minute. It's surprising to students to discover the differences in the physical properties of the peanut after it has burned.(TOC)
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30. Mechanical to Thermal Energy
 A sample of water is heated using a small segment of nichrome wire and a Genecon generator. By measuring the force needed to turn the crank, the lever-arm length, and counting the revolutions needed to raise the temperature of the water 10 degrees Celsius, a comparison of mechanical and thermal energy can be obtained. The student will most likely gain a greater appreciation of 10 cents worth of electricity following this demonstration.(TOC)
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