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Explain Archimedes’ Principle.

Explain Archimedes’ Principle. Archimedes’ Principle states that a fluid will exert an upward buoyant force on any object that is in the fluid. This buoyant force is equal to the weight of the fluid displaced by the object.

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Explain Archimedes’ Principle.

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  1. Explain Archimedes’ Principle. Archimedes’ Principle states that a fluid will exert an upward buoyant force on any object that is in the fluid. This buoyant force is equal to the weight of the fluid displaced by the object.

  2. How is it possible for a boat made of aluminum (D = 2.71 g/cm³) to float in water (D = 1.0 g/cm³)? • A boat that is made of aluminum can float in water because of the shape of the boat. Since it is hollow, air fills most of the volume of the boat, making the boat’s overall density less than that of the water, therefore it will float. Archimedes’ Principle tells us that the upward buoyant force is equal to the weight of the water the boat displaces.

  3. Why do your bare feet hurt more when you walk on rocks in shallow water compared to deep water? • When you walk in shallow water, a small buoyant force pushes up on you (b/c you are displacing a small amount of water), so most of your weight is supported by your feet—OUCH! When you walk in deep water, a large buoyant force pushes up on you, so a lot of your weight is supported by the water and less is supported by your feet—AAAHH! Archimedes’ Principle tells us that the buoyant force is equal to the weight of the fluid displaced by the object.

  4. Why does a helium balloon rise into the sky? • A helium balloon will float into the sky because the density of the balloon and helium is less than the density of the air. There is an upward buoyant force on the balloon that is greater than the weight of the balloon, so it rises. This buoyant force is equal to the weight of the air that is displaced by the balloon, according to Archimedes’ Principle.

  5. What is Pressure? What are the SI units used for describing pressure? What is the equation used to calculate pressure? • Pressure is the amount of force exerted per unit of area. Pascals are the SI units for describing pressure. The equation for calculating pressure is: P = F/A

  6. How much force does the Earth’s atmosphere exert on the ceiling of Room 248 if the dimensions of the room are 7 m wide by 8 m long, and atmospheric pressure is 1.01 x 105 Pa? A = L x W A = (7m)(8m) = 56 m2 F = P x A F = (101,000 Pa)(56 m2) F = 5.656 x 106 N

  7. Explain Bernoulli’s Principle. • Bernoulli’s Principle states that as the velocity of a fluid increases, the pressure exerted by the fluid decreases. In other words, if a fluid is moving (like flowing water or wind), then that fluid pushes with less force than a fluid that is moving slower or not at all.

  8. What is viscosity? List examples of fluids with high viscosity. • Viscosity is a fluid’s resistance to flow. Examples of fluids with high viscosity are honey, syrup, lava, molasses.

  9. Why could it be dangerous to stand near train tracks when a fast-moving train passes by? • It is dangerous to stand near train tracks when a fast-moving train goes by because the train will cause the air right beside it to move fast also. As Bernoulli’s Principle states, as the velocity of a fluid increases, the pressure exerted by the fluid decreases. This means that there will be a low pressure in the fast-moving air right near the train. If you are standing there, then the higher pressure behind you (because that air is not moving as fast as the air in front of you) could push you toward the train and you could get seriously hurt!

  10. How does an airplane’s wing generate lift? • An airplane’s wing is curved on top and flat on the bottom, so that when the plane moves through the air, the air moving over the top of the wing goes faster than the air going under the bottom of the wing. Bernoulli’s Principle states that as the velocity of a fluid increases, the pressure it exerts decreases. This means that there will be low pressure above the wing and higher pressure below the wing. This results in an upward lift force which lifts the plane up.

  11. Why do 2 pop cans move toward each other when a stream of fast moving air is blown in between them? • When a stream of fast moving air is sent between 2 empty pop cans, a region of low pressure is created between the cans according to Bernoulli’s Principle. Since the air on the outsides of the cans is not moving, it is at a higher pressure and will push each can toward the middle.

  12. Explain Pascal’s Principle. • Pascal’s Principle states that the pressure applied to a container of fluid is transmitted equally and undiminished throughout the fluid and in all directions. In other words, if you squeeze a plastic bottle of water, you will increase the pressure of the fluid. This pressure increase is felt throughout the entire bottle of water, on all the inner sides of the bottle.

  13. How does a straw allow you to suck liquid up into your mouth? • When you suck on one end of a straw, you decrease the pressure inside the straw. The liquid (drink) is exposed to this low pressure region inside the straw, but is also exposed to the atmosphere outside of the straw. Since the atmospheric pressure is greater than the pressure inside the straw, the pressure from the atmosphere pushes the liquid up the straw and into your mouth.

  14. How does an index card stay on an inverted cup of water? • A cup is completely filled with water (NO AIR BUBBLES!) and then an index card is placed over the mouth of the cup. When the cup is turned upside down, the card stays over the opening of the cup, holding the water inside. This occurs because inside the cup, there is about 1-2 pounds of force (the weight of the water inside) pushing down on the index card. Since all the air has been forced out of the cup, there is no atmospheric pressure acting on the inside of the card. On the outside of the card, the atmosphere pushes on each square inch of the card with about 15 pounds of force. So if the cup opening’s area is about 7 square inches, there is a force of about 105 pounds pushing up on the card. Since this upward force is much greater than the downward force of gravity, the card does not fall off.

  15. Describe Boyle’s Law, Charles’ Law and Gay-Lussac’s Law. Give an example of each. • Boyle’s Law states that as the volume of a container of gas is decreased, the pressure of the gas increases, as long as the temperature of the gas does not change. For example, if you squeeze an inflated balloon (decrease its volume), the pressure inside the balloon will increase, and the balloon may pop. Charles’ Law states that as the temperature of a container of gas increases, its volume increases, as long as the pressure of the gas does not change. For example, if you place a sealed, air-filled 2-liter pop bottle into a freezer (decreasing the air’s temperature), the bottle will crumple inward, decreasing its volume. G-L’s Law states that as the temperature of a gas increases, pressure increases, as long as the volume does not change. EX: putting spray can in fire = BOOM!

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