Kid Stuff: Water Labs 4.6-8

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Photos (top to bottom): photo1: Ethan using a plastic pipette to place drops of water on a 200 CFA coin; photo2: Alice, Emilie, Tori and Rosa; photo3: Ali creating a meniscus in a vial of water; photo 4, 18, 19: floating a paperclip on water's skin; photos 5, 8, 12, 15: water beading on the surface of a coin, a consequence of the cohesive properties of the sticky, polar water molecules; photos 6&13: soap weakens the hydrogen bonds between water molecules, and alcohol, a non-polar liquid, lacks cohesion and so does not bead; photo7: Luciana, Dalia & Goundo; photo9: Kosuke; photo10: Catherina; photos 11&14: Margret; photo16: Gabriel at floor-eye view; photo17: Aleah.

Five labs on surface tension (all common surface tension-related experiments widely documented on the web):

LAB1: Floating Paperclip/Needle

• Fill the bowl with water

• Try to make the paper clip float...not much luck, huh?

• Tear a piece of tissue paper about half the size of a CFA bill

• GENTLY drop the tissue flat onto the surface of the water

• GENTLY place a dry paper clip flat onto the tissue (try not to touch

the water or the tissue). Use the eraser end of the pencil to carefully

poke the tissue (not the paper clip) until the tissue sinks. With some

luck, the tissue will sink and leave the paper clip floating!

• Add a drop of liquid soap to the water. Observe what happens.

LAB2: Run-Away Pepper

Put water in your container. Sprinkle some pepper into the bowl until

you have an even layer of pepper floating on top of the water. Carefully squeeze a drop of liquid soap into the middle of the bowl. Observe and record what happens!

LAB3: Motorized Paper Fish

Needed materials:

• paper fish

• scissors

• liquid soap

• a large bowl or loaf cake pan full of water

Once you have your paper fish pattern cut out, place it on the water container so it floats on the surface. Put a drop of the oil or detergent in the hole in the middle of the fish.

The detergent or oil will cause the surface tension in that hole to drop. This will cause the fish to propel forward, leaving a trail of the oil as it moves across the water, not stopping until the oil has lowered the surface tension of the entire bowl.

LAB4: Over-The-Top

Fill a glass with water just past the rim without spilling. Place a soapy finger on the surface of the water. Can you guess what will happen?

LAB5: Knotty string

Knot a piece of string into a loop and allow it to float in a bowl of water. If you dip a match into the middle of the irregularly shaped loop, it immediately becomes circular.

The match has this magic power because it was previously dabbed with a little washing-up liquid. This spreads in all directions when the match is dipped into the water and penetrates between the water particles, which were held together like a skin by surface tension. This ‘water skin’ breaks in a flash from the place where the match is dipped in outwards. The liquid particles, which are made to move, push against the loop and make it rigid.