Amy Sass
Floating Objects
Science Concept: Density, Hydrogen Bonding/Surface Tension To demonstrate that the surface tension of water can cause objects to float on the water. To demonstrate that the surface area and density effects whether or not an object will float.
Materials:
1000 ml beaker
800 ml of water
1 yen coin
1 dime
1 pop can top
1 paper clip
5 ml of dish detergent
paper towels
pencil
Directions:
Measure 800 ml of water and pour it into the 1000 ml beaker.
Show the audience that dime and the Yen coin look alike.
Put the dime in the water. (it sinks)
Carefully put the yen in water (it floats).
Put a piece of paper towel in the water. Let it soak up with water. Then put a paper clip on the wet paper towel. Push the paper towel down with a pencil. The paper clip will remain floating.
Carefully put pop can top in water. (It floats).
Add the detergent.
Introduction:
Boys and girls, I have a very magical dish right in front of you. I can tell my dish to make things float and then I could tell my dish to make things sink. Would you like to help me tell my magical dish what to do? Show them the yen coin and the dime. Hold up the dime and tell the kids to say Magic dish, may this coin sink, drop in the dime, it will sink.
Explanation:
Density and surface tension play a big role in this experiment. All objects have a density, and some objects float because of surface tension. Surface tension is when the water forms a close net of bonds among all of the water molecules that do not allow the objects to break through these bonds. Surface tension, almost creates an imaginary net on the surface.
When I added the dish detergent to the dish, the objects sank. The soap molecules in the dish detergent were able to break through the bonds that the water had created. Picture little army men busting through a wall, that is what the soap molecules were. The soap molecules broke the bonds, and since the objects were "resting" on the bonds, they were forced to sink because the bonds were taken away.
Another reason some things float and others do not (even if they are the same size), is because of density, and/or surface area. The two coins have the same surface area (they are the same size), but the dime is denser. So the dime is heavier and is able to break through the strong water bonds and sink. When an object is less dense it will float. The yen, paper clip, and pop top were less dense then the water they were in. When an object is more dense than the liquid it is in, it will sink (i.e. dime).
Safety Precautions:
Do not swallow any soap
Do not put any small pieces in your mouth
Waste disposal:
Take all objects out of beaker
Pour the soapy water down the drain
Rinse out beaker completely
References:
Reference: Summerlin, L.R, Ealy. J.L, Chemical Demonstrations Vol. 2 - A Sourcebook for Teachers, American Chemical Society, 1987, p. 19.