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This activity aligns with the following National Science Education Standards: The following is a simple exercise that demonstrates how steam can be harnessed to create mechanical energy. (For a more detailed look at how a steam engine operates, refer to On Track with Science: How to Build a Miniature Steam Engine.) A steam engine converts heat energy into mechanical energy. When water is heated, it becomes water vapor, and its volume increases about 1,600 times. The increased volume of water vapor produces a force that is used to operate a mechanical structure. Such engines once ran most trains, ships, factories, and some cars. In about A.D. 60, a man named Hero used wood to boil water, and he proceeded to use steam from the boiling water to power an engine. Students can create their own version of Hero's engine by using a small, metal spice can with a press-on metal lid, a nail, a hammer, water, string, a hot plate, and a ring stand. First, near the top of the can, use the hammer and nail to carefully punch two holes on the opposite sides of the can. Pour about 10 mL of water into the can. Next, place the string under the lid and attach the lid to the can so that equal lengths of string come out of each side. Hang the can from a ring stand, making sure that it hangs without twisting. Place the hot plate under the can. Make sure not to touch the can. Ask students to describe what happens after the water begins to boil and produce steam. How would they describe the motion of the can? (The can begins to rotate.) This activity aligns with the following National Science Education Standards: Today, trains pull more massive loads than ever before. Although improved design has reduced friction over the years, additional mass continues to increase both the friction on the tracks and the amount of energy required to pull the train. To help students understand how mass affects friction, obtain four textbooks, a one-meter piece of string, and a spring scale. Follow this procedure:
What happens to the force needed to pull the books as the number of books increases? How does an object's mass affect the force of friction? From a graph of the data, can you predict the force needed to pull more than four books? Can you draw an analogy between books and trains, and the number of locomotives needed to pull more railroad cars? These activities align with the following National Science Education Standards: In old movies and cartoons, train robbers sometimes place their ear on a railroad track to check for an oncoming train. Students can learn why this method works by exploring how sound travels at different speeds in different media. Use a metal coat hanger, a one-meter-long piece of string, and a one-meter-long piece of thin gauge copper wire. First, tie the middle of the string around the hook of the hanger. Wrap one end around your left index finger and the other end of the string around your right index finger. Then, gently tap the hanger against a table. Listen for the sound it makes. Next, with the string still wrapped around your fingers, put your fingers in your ears and tap the hanger again. What do you notice about the sound? Repeat steps, this time using the wire. Which is the better conductor, the string or the wire? (The wire is better) Why? (Sound travels faster through the wire than through the string.) For a simpler demonstration, lay your ear on a wooden table as someone taps it. Then rest your head on your arm and listen for the tapping. You can also put a pillow between your ear and the table. As an extension, research whether certain materials conduct sound better than others. (The speed of sound is dependent on temperature and the medium through which the sound travels. In solids, atoms are usually closer together, which is why solids transmit sound faster than air does.) THE DOPPLER EFFECT Have students research the practical applications of the Doppler effect. (Most radar depends on the Doppler effect to locate and determine the speed of objects. The police use Doppler radar to identify speeding motorists.) As an extension, invite a local weatherman to discuss how Doppler radar is used to forecast weather, or have a land surveyor talk to the class about how Doppler satellite receivers have been used to determine geographic positions in remote areas. This activity aligns with the following National Science Education Standards: Periodically, one will read in newspapers about train derailments resulting from the thermal expansion of metal tracks. Ask students if they have ever run hot water over a jar's metal lid because it was too tightly closed to open. Why does this help? (Because the metal expands under the heat of the water, just as train tracks can expand in high temperatures.) Expansion must be taken into consideration when designing railroads, highways and bridges. Have students research the measures that engineers employ to prevent concrete roads from cracking or buckling, and trains from derailing. (For example, concrete bridges and highways are built with expansion joints to allow for the expansion and contraction of the construction materials.) These activities align with the following National Science Education Standards: Studying trains is a good way to study different types of engines and the evolution of energy efficiency through the years. The earliest locomotives, powered by wood and coal, were highly inefficient because much energy was converted into thermal energy that escaped into the atmosphere. An engine is energy efficient when it minimizes the loss of useful energy. Have students learn about the energy sources and workings of different types of train locomotives and answer the following questions:
ENERGY TRANSFORMATION As an extension, have students create simple toys that use conversion of energy to create motion. They may use wheels, rubber bands, propellers, and dowels. Have students explain the transformations of energy that occur. This would include the energy they use to push or pull the toys, as well as energy released from the unwinding of rubber bands and so on. |