Buoyancy and Density

1. Buoyancy and Density Unit 2: Fantastic Fluids Chapter 5: Density and Buoyancy

2. Review • Define fluid. • Examples of a fluid. • Define viscous. • Which has a faster flow rate, a high viscous fluid or a low viscous fluid? • Which fluid was most viscous? • Which fluid was least viscous?

4. Archimedes of Syracuse (287 B.C. to 212 B.C.) • Why is he important? • He is basically the first person to relate buoyancy to density. • Quick Biography • Greek mathematician, philosopher, and inventor • He built rock-throwing catapults, grappling hooks, and lenses or mirrors that could allegedly reflect the sun's rays and cause ships to catch on fire. • Levers • Pulleys • Killed by a Roman solider

5. Archimedes Screw http://www.youtube.com/watch?v=5gq3Vm4vifU&feature=related&safety_mode=true&persist_safety_mode=1

7. Italy

8. Buoyancy • The ability to float in water or air. • Examples (water): • Examples (air): • Non-examples:

9. Buoyant Force • The upward force exerted on objects submerged in fluids is called buoyant force. • The downward force exerted on objects submerged in fluids is called gravity.

10. Testing for Buoyancy

11. Buoyancy Cont’d • Why did some objects sink and some float? • The particles in the objects that sank have less space between them than the particles in the fluid they were placed in. • That is to say, the particles in the object are packed tighter, therefore the object has a greater density than the fluid. • Draw example on white-board.

12. Density and the Particle Theory of Matter • In everyday words, density can be described as the “crowdedness” of the particles. • The less space between particles, the more dense the object. • The more space between particles, the less dense the object.

13. Density - Dolphins • http://www.youtube.com/watch?v=JNJG1uZQ_dQ&safety_mode=true&persist_safety_mode=1

14. Density – Dolphins Cont’d (Draw) • How is that possible? • The particles in the water have much more space between them allowing the dolphin to easily cut through the water. • Similarly, objects that sink have less space between the particles and are more densely packed therefore they can “cut” through the water. • However, objects with more space between their particles in juxtaposition to the water particles will not cut through the water and stay afloat. You can sink them by applying downward pressure, through which you are simply helping gravity do it’s job.

15. Drama Component • Solid, liquid, gas • Attractive force???

16. Measuring Density • We now know that objects that sink have “more” particles inside them, than the fluid they are dropped in. So objects that sink are denser. (Refer to D on B) • There is actually a formula that allows us to determine the density of objects. • The formula tells us how much mass the object has for every cubic centimeter. • Lets say you have an object with a density of 5g/cm³. If you cut the object into pieces equal to 1 cm³, each piece has a mass of 5 grams

17. Determining Density • Dimensions of a wooden block • Length - 5 centimeters (cm) • Width – 2 cm • Height – 4 cm • Mass • 80 grams (g) • Do several examples • Change numbers and have students do on their own. • Density = mass/ volume

18. Displacement • The amount of water that an object displaces is equivalent to it’s volume • 31 grams=31 milliliters

19. Lesson 4

20. Archimedes and the Golden Crown The king of Syracuse, Hiero, wanted a golden crown. He weighed a lump of gold and ordered a goldsmith to make him a crown with it. The goldsmith returned with a crown that weighed exactly the same as the lump of gold. The king was happy. After a while, however, the king grew suspicious. The goldsmith might not have put all the gold into the crown. He might have used some other metal. The king called Archimedes to help him determine whether any other metal had been mixed into the crown.

21. Archimedes thought and thought, but he couldn't figure out a way to determine whether the goldsmith had melted silver in the crown. One day he decided to go to the baths. As he got into the tub, some water sloshed out. He had solved his problem. Archimedes ran out on the streets shouting "Eureka, Eureka!" He was so excited that he hadn’t bothered to put his clothes on! The experiment was very simple. Archimedes filled a jar to the brim, dropped the crown in it, and gathered the water that flowed out. Then he replaced the water in the jar and dropped in a lump of gold the same weight as the crown. He found that the lump of gold caused less water to overflow than the crown. This meant that the crown occupied more volume, or space, than the lump of gold. This, in turn meant that the crown was not all-pure gold and that the king had been cheated.

22. What Does This Tell Us • The amount of water that is displaced is equal to the volume of the object. • For example, if an object displaces 25 ml of water, the object is equal to 25 cubic centimeters. • Thus, by determining the mass of an object and its volume we can actually determine the density of irregular shapes. • By comparing the densities we can determine whether objects will float or sink in different fluids

24. How Do Submarines and Animals Control Depth • http://www.youtube.com/watch?v=YNj2xrschr4&feature=related&safety_mode=true&persist_safety_mode=1