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Learning Goals

Learning Goals. Define buoyancy. Explain the relationship between density and buoyancy. Discuss applications of Archimedes’ principle. Mass. Mass is the amount of matter that makes up an object.

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Learning Goals

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  1. Learning Goals Define buoyancy. Explain the relationship between density and buoyancy. Discuss applications of Archimedes’ principle.

  2. Mass • Mass is the amount of matter that makes up an object. • A golf ball and a ping pong ball are the same size, but the golf ball has a lot more matter in it. So the golf ball will have more mass. • The mass of an object will not change unless we add or subtract matter from it.

  3. Weight • Weight is a measure of the force of gravity on an object. • Your weight can change depending on the force of gravity. The gravity will change depending on the planet you are on.

  4. Volume • Volume is the amount of space contained in an object. • We can find the volume of box shapes by the formula Volume = length x width x height • In this case the units would be cubic centimeters (cm3). • So a box 2 cm x 3 cm x 5 cm would have a volume of 30 cm3 V = L x W x H

  5. Liquid Volume • When the metric system was created, they decided that 1 cm3 of water would equal 1 milliliter of water and the 1 mL of water will have a mass of one gram. • 1cm3 water =1 ml of water = 1 gram

  6. Water displacement • We can use water displacement to find the volume of objects that are not boxed shaped. • We can put water in a graduated cylinder. If a rock causes the level to rise from 7 to 9 ml, the the rock must have a volume of 2-mL.

  7. Density • Density is the amount of matter (mass) compared to the amount of space (volume) the object occupies. • We will measure mass in grams and volume in ml or cm3 • Density is mass divided by volume. • Density = mass/volume

  8. Buoyancy is a force Buoyancy is a measure of the upward force a fluid exerts on an object that is submerged. The water in the pool exerts an upward force that acts in a direction opposite to the boy’s weight.

  9. Volume and buoyancy The strength of the buoyant force on an object in water depends on the volume of the object that is underwater. As you keep pushing downward on the ball, the buoyant force gets stronger and stronger.

  10. Brain pop video • http://www.brainpop.com/science/motionsforcesandtime/buoyancy/

  11. Archimedes’ Principal In the third century BC, a Greek mathematician named Archimedes realized that buoyant force is equal to the weight of fluid displaced by an object. A simple experiment can be done to measure the buoyant force on a rock with a spring scale when it is immersed in water.

  12. Weight and buoyancy Weight is a force, like any other pushing or pulling force, and is caused by Earth’s gravity. It is easy to confuse mass and weight, but they are not the same. Weight is the downward force of gravity acting on mass. What is the rock’s weight? What is the rock’s mass?

  13. Sinking and floating In air the buoyant force on the rock is 29.4 N. • When the rock was submerged, the scale read 19.6 N. • The difference is a force of 9.8 N, exactly the amount of force the displaced water exerts.

  14. Sinking and floating These blocks are the same total volume. Which block has more buoyant force acting on it? Which block weighs more in air?

  15. Sinking and floating • Buoyancy explains why some objects sink and others float. • Whether an object sinks or floats depends on how the buoyant force compares with the weight. • If an object weighs more than the weight of the water it displaces, it will sink. If the object weighs less, it will float http://videos.howstuffworks.com/discovery/6540-mythbusters-lets-talk-buoyancy-video.htm

  16. Density and buoyancy If you know an object’s density you can quickly predict whether it will sink or float. Which ball will sink in water? Which ball will float in water?

  17. Density and buoyancy When they are completely underwater, both balls have the same buoyant force because they displace the same volume of water. • However, the steel ball has more weight since it has a higher density.

  18. Boats and apparent density Apparent density determines whether an object sinks or floats.

  19. Apparent Density An object with an apparent density GREATER than the density of water will sink. An object with an apparent density LESS than the density of water will float.

  20. Buoyancy, volume, temperature, and pressure of gases A hot-air balloon floats because the air inside is less dense than the air outside. The balloon example illustrates an important relationship, known as Charles’s law, discovered by Jacques Charles in 1787.

  21. Investigation 10C Key Question: How can mountains float? Mountains and Earth’s Crust

  22. Buoyancy https://www.youtube.com/watch?v=xniW3_afO-0

  23. Boat-in-Pool Puzzler Here we have a boat in a swimming pool. In the boat is an inquisitive experimenter. Also in the boat is a rock.Our experimenter picks up the rock and tosses it into the pool. The rock sinks to the bottom. No water leaves the pool from the splash made by the rock.Now for the question: Does the pool's water level rise, lower, or stay the same? The water level rises. The water level lowers. The water level stays the same.

  24. Water Level Lowers You think that the pool's water level will lower? That's absolutely right!The reason is that, when the rock is in the boat, it displaces its total weight. If it weighs ten pounds, for example, then it's making the boat ten pounds heavier. When the rock is sitting at the bottom of the pool, on the other hand, it displaces its volume. As an object sinks when it weighs more than the water it displaces. To follow the example given above, the ten-pound rock may only displace three pounds of water. (A given volume of rock is typically three to five times heavier than the same volume of water.)At any rate, the rock displaces more water when it's in the boat than when it's in the water, and so the pool's water level is lower when the rock is in the water.

  25. Why Did the Titanic Sink?

  26. So how can a ship float? • A ship can float because it’s constructed with many air-filled chambers. • Air, as we all know, weighs less than water • So, the combined weight of the air and steel of the ship weighs less than the weight of the water displaced by the ship • So, the ship floats!

  27. What Happened to the Titanic? It was Archimedes’ Principle! • The “unsinkable ship” was en route to NYC in 1912 • On April 14, it struck an iceberg • The collision ripped a huge hole in the hull of the ship, causing the air filled pockets to fill with water • This added weight became greater than the buoyant force supporting the ship, so it sank. Rapidly. • About 1500 lives were lost

  28. Let’s Sum it Up! • An object sinks when the weight of the object is greater than the buoyant force that supports it (quarter) • An object floats when its weight is less than the buoyant force that supports it (Aluminum foil) • Archimedes’ Principle is that the BF=weight of object in air-weight of object in water or the BF=the weight of liquid displaced=loss of weight in liquid

  29. Iceberg • Icebergs float. • 90% of the iceberg is underwater • They are made of freshwater not saltwater

  30. Let’s go to the Video! ..\Titanic\9ab. Buoyancy_and_the_Titanic 8.35.mov

  31. Now it is your turn to try to make an unsinkable ship!

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