![[IMAGE]](Ship.gif)
Lab # 7
How is density related to Floating objects ?
To Float or not to Float ?
2 Kings 6:5 But as one was felling a beam, the axe head fell into the water: and he cried, and said, Alas, master! for it was borrowed. 6 And the man of God said, Where fell it? And he shewed him the place. And he cut down a stick, and cast it in thither; and the iron did swim.
PROBLEM:
How to determine the Density of a Floating object !
MATERIALS:
SBB, Graduate Cylinder, Eye dropper, Thin thread, Two very small glass or plastic containers, (a) .3 Fluid ounce plastic container ( dimensions, about 2 and 1/2 inch long and about 3/4 inches wide, at the base ) ; and a (b) small tablet container nation wide brand, initials are " Ty " that held about 10 tablets, with plastic label removed, and whose dimensions are 7/8 inch wide and about 2 and 3/4 inch long, used here, A gallon plastic container, half filled with water.
PROCEDURE:
1. Used here, a " Baking Food Color Set " commercial name " Decacake" .3 Fluid Ounce plastic container, (a) almost full, as is from the store, just make sure the cap is on tight. (b) small tablet container with about 20 grams of salt added, so that it will float vertically, total weight was about 30 or so grams. Tie a thin thread ( the length will be determined by how far from the gallon plastic container ) to the necks of each container.
2. Record the weight of each small plastic container, with its contents. Again the ideal would be, to have the sample float vertically, in water, so if the container is a discarded container, try adding salt to the container so that it will float vertically.
3. Fill the Graduate Cylinder to the exact 60 ml mark, use an eye dropper to adjust the level.
4. Gently slide in the small plastic container (a) into the Graduate Cylinder. And record the rise of water in the Graduate Cylinder. Again, you are going to have estimate the exact volume, because your Graduate Cylinder is only calibrated to the 5 ml mark, so use your judgment as to the exact ml. You can tell how much above the 5 ml mark it would be.
5. Now using a straighten paper clip, fully submerge the floating object and record its volume. Again, you are going to have estimate the exact volume, because your Graduate Cylinder is only calibrated to the 5 ml mark, so use your judgment as to the exact ml. You can tell how much above the 5 ml mark it would be.
6. Now, repeat the above steps for small container (b), be sure to check the level in the Graduate Cylinder, you might have to add a few drops, so that the level would read 60 millimeters.
7. Now here is the tricky part ! Weigh each object in water, using a plastic gallon container, as you did in weighing the metal objects. But this time make sure there is a slight slack in the thread when you are trying to weigh it. Record your results.
OBSERVATION:
| Weight. of container | Total Volume of container submerged | Volume displaced while floating | Weight in water | |
| Small container (a) | ||||
| Small container (b) | ||||
Mass |
|
Density = |
----------- |
Volume |
1. How much did the object (a) weigh ? ______; (b) weight ? ______
2. How much volume did the object (a) displace when it was floating ? (a)____ , (b) ____
3. How much volume did the object (a) displace when it was submerge totally under water ? ____, (b) ______
4. How much did the object (a) weigh in water, with a little of slack in the thread ? ______ , (b) _____
5. What is the density of the Floating object (a), (b) ? Use the weight in air and the total submerged volume.
QUESTIONS:
1. Define specific gravity .
2. What are the units for density ?
3. What are the units for specific gravity ?
4. What connection can you observe between " Weight in air" and displacement of water ?
5. For every ml of water an object displaces; How much less does the object weigh in water ?
6. Define Buoyancy.
7. How can you measure Buoyancy .
8. What are the units for Buoyancy.
9. If an object weighs 75 grams in air and displaces 14 ml of water. (a) How much Buoyancy is there ? ( b ) How much does the object weigh in water ?
10. When does an object float in water ? How is this related to its density ? Explain.
11. What are the metric units that can be used to express volume ? How is this possible ?
12. Here is a problem; suppose you have a 40 gallon aquarium tank, four feet long, and exactly in the middle of the aquarium is a floating toy ship, and the whole aquarium is balanced on a small three inch triangle, which serves as the pivot point . Now, what would happen if you would gently move the toy ship to the extreme right, while some one would support the tank from moving. Would the tank tip to the right ? Explain !
13. Would you believe that a ship could be made out of cement, and that there are some recks of ships that can still be found on our coast lines ! Find out when they were built .
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