Experiments for Buoyancy With a Hydrometer

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    Salt or Not?

    • Make a salt and water solution by adding table salt to one cup of water until no more salt will dissolve. Add several drops of food coloring and fill a graduated cylinder 3/4 full with the salt water. Measure one cup of water into a cup and add several drops of the same color food coloring. Fill an identical graduated cylinder 3/4 full with the colored tap water. Have a friend move the cylinders so you cannot tell which one is the salt water. Put the hydrometer into each graduated cylinder one at a time and read and record its level. Compare the readings and identify the salt water. The salt water is more dense than the tap water and is more buoyant.

    Salt Water Solutions and Buoyancy

    • Number four graduated cylinders with a small piece of paper taped to the bottom. Prepare four different salt-water solutions, using one cup of water for each solution. Add a different amount of salt to each cup of water. Record the amount of salt added to each cup. Put the water with the least salt in cylinder #1 and continue in order of the amount of salt. Fill each cylinder 3/4 full with one of the salt-water solutions. Record the cylinder number for each solution. Ask a friend to switch the order of the cylinders. Measure the density of each solution with the hydrometer. Check the number of the bottom of the cylinder to see if you are correct.

    Comparing Buoyancy in Liquids

    • Compare the density of corn syrup, dishwashing liquid, oil and tap water by pouring each liquid into its own graduated cylinder. Put the hydrometer in each cylinder one at a time and read and record the level. Clean the hydrometer between tests. Put the cylinders in order from least dense to most dense. Compare the buoyancy of several items, such as a penny, marble or small screw, by dropping them one at a time into each cylinder and noting whether they float or sink, and how fast. Clean off the items between cylinders.

    How Can You Make an Egg Float in Water?

    • Let two uncooked eggs come to room temperature. Fill two glasses with water. To one glass, add six tablespoons of table salt and stir. Put the hydrometer in each of the glasses, read the levels and record the data. Based on the hydrometer reading, decide which glass has water that is more dense and more buoyant. Put one egg in each glass. The salt in the second glass made the water more dense and made the egg float.

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