The following examples show how "common" sense can sometimes lead to the wrong answer.
- Tailgate down give better fuel mileage.
- Incorrect: An open pickup truck bed is bad for gas mileage because it catches the air and creates drag, so the easy, zero cost method for increasing mileage by reducing drag is to drive with the tailgate down thereby letting the air escape.
- Correct: An open bed with a closed tailgate creates a dead air space in the bed. Air coming over the top of the cab is kept out of the bed by this dead air and smoothly flows over the bed.
- See: Gas Mileage and Pickup Tailgates and Car Talk.
- A Cooling Tower is not a Nuclear Power Plant.
- Incorrect: A cooling tower such as the one shown here is a nuclear power plant.
- Correct: The photo shows a cooling tower. It might be used to cool hot water from a nearby nuclear power plant or it might cool water from a gas-fired power plant as in the photo from Chengdu, China. (Notice the smoke stacks.) Such towers are also used to cool coal-fired power plants. Also some power nuclear power plants such as those near Phoenix, AZ have low flat cooling structures because of the lack of water. And nuclear power plants near an ocean use the ocean water for cooling.
- The earth is only 5000 years old.
- Incorrect: In the 19th century, it was argued that the earth could not be more 5000 years old based on Newton's law of cooling.
- Correct: The earth is much older than 5000 years. Radioactive decay continues to create heat within the earth. Of course, radioactivity was unknown in the 19th century.
- The earth is at the center of the solar system.
- Incorrect: If earth rotated about sun, the earth's surface would have to move at 1000 mph and then there would be great winds on the earth's surface.
- Correct: The earth does rotate about sun and the surface does move about 1000 mph. The atmosphere moves along with the surface so winds do not move faster than about 100 mph.
- The moon orbits the earth from east to west.
- Incorrect: The moon rises in the east and sets in the west. Therefore, it orbits the earth in the opposite direction of other solar-system bodies.
- Correct: The moon orbits the earth from west to east as do most other solar-system bodies. However, since the earth rotates on its own axis at a higher angular velocity, it appears from the earth's surface that the moon is going from east to west. But from outer space both earth and moon appear to orbit the same direction.
- Protect oysters by cutting sea stars in half.
- Incorrect: At one time, oyster workers would remove sea-star predators from the beds, cut them in two, and throw the parts back into the beds.
- Correct: The sea star halves re-grow the missing parts. Thus the workers were increasing the numbers of sea stars rather than reducing them.
- Third place is second place.
- Incorrect: If the highest two winners are tied they share the first-place award. The second-place award goes to the next highest.
- Correct: Third place means that there are two higher winners. It doesn't matter if those two are tied or not. Therefore, if there is a tie for first place, there is no formal second place award and the next award is third place. For horse races, the prizes for first and second place are divided equally between the two who are tied.
- Diesel engines get better fuel mileage than gasoline engines.
- Misleading: Diesel cars get better miles/gal than gasoline cars.
- Correct: Comparing diesel to gasoline engines using mpg is like comparing apples to oranges. Most hydrocarbon fuels have about the same energy per pound, but some, like gasoline, are lighter than others, like diesel fuel. Thus, a pound of diesel fuel has about the same energy as gasoline, but a gallon of diesel fuel has 130,500 Btu while a gallon of gasoline has only 115,000 Btu. Thus a gallon of diesel fuel has 13% more energy and should always give at least 13% better miles/gal. If we compared diesel to gasoline engines on miles per pound, they would be closer.
- Buy long-life light bulbs to save money
- Incorrect: long-life light bulbs save money.
- Correct: A light bulb is cheap compared to the electricity is uses. For example, if a 100-watt bulb lasts 750 hours it uses 75-kw-hrs of electricity in its lifetme. If electricity is $0.11 per kw-hr, the total cost is $8.25 plus the bulb price. Long-life bulbs produce less light for the electricity used so a higher wattage bulb is needed to get the same amount of light as with a regular 100w bulb.
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