Subject Area Lessons

## #224. Surface tension on coins

Science, level: Middle
Posted by Craig Hunter (huntcd@infinitytx.net).
Lesson Plans for Middle School Science
West Texas Middle School, Stinnett, Texas
Materials Required: Coins, dropper bottles, soapy water and water
Activity Time: 35 minutes or more if a graph is involved
Concepts Taught: Surface Tension

Surface tension on coins

The purpose of this activity is to study surface tension, and the
effect that soap has on surface tension....well actually to attempt to
get teenagers to develop a few reasoning powers in their harmone-crazed
brains.

Materials needed:
Coins: pennies, nickels, dimes, quarters (acutally I also use half
dollars, and small and large silver dollars....left over from the tooth
fairy years ago)

Eye droppers (one per group)
Water in a bottle (one per group)
Soapy water in a bottle (one per group)
Paper towels for clean up

Step 1. The students should clean the coins in plain tap water to make
sure that there isn't any soap left on them from the last class. If
you're not sure that the previous class cleaned the eyedroppers with
fresh water, they should clean the droppers also.

Step 2. The students should get their bag of coins (whatever coins
you've decided to let them use). They should then place a coin on a
paper towel and begin dropping water on the coin until the water
overflows. They should record how many drops the coin held before the
water overflowed. This number should be placed under a heading called
"Plain Water." This procedure should be repeated with the remainder of
the coins.

Step 3. The students should then find out how many drops of soapy water
each coin will hold before the water overflows.

Step 4. The students can then make a color coded, double bar graph
which indicates how many drops of water each coin held.

Step 5. The students should then draw conclusions according to their
data.

Step 6. The students should then clean the coins and the eyedroppers
with fresh water for the next class.