Water, Water, Everywhere

    April 2017:


    • Paper or Styrofoam cups
    • Ink pen
    • Pencil
    • Water bottle with cap
    • Push pin


    A)   Begin by pushing the pen into the cup about 1 inch from the bottom and follow with two more holes, each 1 inch above the previous one. Above the sink or a tub, plug the holes with your fingers and pour water into the cup. Release your fingers from the holes and notice the water coming out of the holes. You can also see a similar effect if you close off the top two holes with your fingers and then take your fingers off the holes.

    B)   The following step might work better outdoors. Make those holes bigger by pushing the pencil through those holes. Again, plugging those holes with your fingers and filling the cup with water, allow the cup to drop to the ground. Pay close attention to the water and where it comes out of the cup.

    C)   Fill the water bottle with water and cap it. Using the push pin, make several small holes in the bottle (anywhere you like). Notice what happens to the water if you leave the bottle alone. What happens if you open the bottle?

    What’s happening?

    For the first experiment you may have noticed that the water is coming out of the bottom hole farther than the middle hole and that water is coming out farther than the hole on top. Because the water pressure is greatest on the bottom, it will push the water out with greatest pressure on the bottom and the water on top may just dribble out of the top hole. If you closed off those top two holes and then released them, you may have seen the water decrease its flow out of the bottom hole because the water pressure is greatest when there are fewer holes for the water to come out of.

    In the second experiment, the water doesn’t come out of the holes at all because the water comes out of the holes as it tries to get to the Earth’s surface due to gravity. But if the water is already falling because of gravity as you release the cup, there is no incentive for it to pour out of the holes so it just stays in the cup (till it hits the Earth).

    Lastly, water stays in the bottle if the lid is on because there isn’t enough pressure to push the water out. Once you open the lid, air molecules can enter into the top of the bottle and create extra pressure to push the water out. If you seal the bottle again there will soon be too little air to push more water out again. If you pick the water bottle up by the neck you can move it around with no water coming out but if you pick the bottle up by the flexible plastic, you will create pressure inside the bottle and water will come out of the holes.


    To view all past “ChemShorts for Kids”, go to:

    - Paul Brandt