Science Corner: Surface tension with a penny, dish soap and cardboard

Science Corner

MOBILE, Ala. (WKRG) – In today’s Science Corner experiment, see how surface tension works in two different experiments! One using a penny and the other using dish soap to propel a cardboard boat!


NECESSARY SUPPLIES: Penny, water dropper (pipette), water

STEPS (check out the video for visuals):

  1. Fill water dropper with water
  2. Add one drop at a time onto the penny
  3. Watch what happens

EXPLANATION: Have you ever seen a bug walk on the water? This is because of surface tension! Water is what we call cohesive. This means that the water molecules want to stick and group together. This happens because water (H2O) has two hydrogen atoms (positive) and one oxygen atom (negative). The negative oxygen atom is attracted to the positive hydrogen atom, so the molecules stick together. This grouping forms surface tension.

Pennies have a small ridge around it. When you drop water on the penny, it forms a dome on the penny. This is possible because of surface tension! Eventually the water will become too much for the penny and it will spill over.


NECESSARY SUPPLIES: Glass dish filled with water, dish soap, cardboard boat, water dropper (pipette)

STEPS (check out the video for visuals) –

  1. Put cardboard boat in water
  2. Drop one or two drops of dish soap into water behind boat
  3. Watch it move without touching it!

EXPLANATION: Due to surface tension (explained above) in addition to other processes, the boat can float on water. Dish soap breaks down and decreases this surface tension by breaking the water molecules apart. Water wants to move from low to high surface tension, so its molecules start moving from the lower surface tension (where soap was dropped) to higher surface tension on the other side of the dish which is what propels the boat!


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