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It’s that wonderful time of year again, and the excitement of going back to school will soon start flooding your neighborhood. Occasionally, your child may begin to feel a bit anxious or nervous at the thought of going back to school. Picking out a special outfit to be saved for the first day or having them shop for (and pack!) their own lunches are tips that have helped ease many a child’s worries. But who wouldn’t want an extra special trick up their sleeves to spice up the recess crowd? Try out our Wet String Magic experiment below and learn about surface tension at the same time. Back to School is the perfect time to get excited about learning!

Bugs can walk on water because of surface tension!

Concept:

This activity explores surface tension.  Surface tension is an attractive property of the surface of a liquid. It is what causes the surface portion of liquid to be attracted to another surface, such as that of another portion of liquid.  In the activity below, the surface tension of the water in a cup to the water soaked into a string will hold every drop on the string when pouring water from one cup to another.

Objective: To move water from one cup to another cup over a string.

Materials: Cotton string, one full cup of water, one empty cup, and food coloring.

Procedure: Cut several 6” pieces of cotton string.  Fill a cup with water and add some food coloring.  Soak YOUR 6” piece of cotton string in the water until it is fully wet. This is VERY important; your string must be wet.  Keep the remaining strings dry for your friends to use.  Remove the string from the water and set aside.

Put the empty cup next to the full cup of colored water.    Place one end of the string into the empty cup and the other end in the cup of colored water.  (It would be a good idea to place paper towels under the cups just in case you spill a little.  Better yet, try this outside!)

The water molecules will follow each other down the string.  Explanation: SURFACE TENSION, or that “skin” created by molecules grabbing onto each other because of their attraction to each other, will keep each and every drop of water flowing down the string into the new cup.

Now for the fun part!  Challenge your friends to do the same, but do not give away your secret that the string needs to be wet! 

• Give them a piece of DRY string and let them try to match your water pouring skills!  Watch as they try to duplicate your results, knowing that water does NOT flow down the DRY string.

• Try your WET string again to show how EASY it is, then give them another piece of DRY string!

• Why do you think the wet string works when the dry one does not?

If you enjoyed this string magic trick, check out our Magic Science Kit with materials and instructions for 11 different activities!

Go there now!

Magic Science Kit

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