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by Procheta Mallik

Introduction

Insert two pieces of straw through a bottle cap. One terminates close to the cap and the other nearer to the base. Observe the flow rate of the liquid from the bottom straw after filling the bottle with coloured water.

    • Take care while handling the scissors.

    • Make sure you conduct the experiment in a place where you can drain the water.

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  1. Take two identical caps compatible with the bottle you are going to use.
    • Take two identical caps compatible with the bottle you are going to use.

    • Glue one cap over the other such that you can invert and use both caps with the bottle.

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    • Heat the end of a metal wire on a candle flame

    • With the heated wire, make holes through both the caps.

    • Do not place your fingers or palm beneath the bottle cap while you are making the hole; you could burn yourself with the heated metal as it suddenly pierces the caps

    • If the hole is not big enough for the "long stiff straw" to go in, trim it off with scissors to make it big.

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    • Insert a long stiff straw piece through the glued caps.

    • Place it in such a way that only about 2 cm of straw protrudes through the inverted cap

    • Use enough glue to seal the straw-cap interface.

    • Leave it undisturbed for 5 min for the glue to dry.

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    • Using heated wire, make a hole on the side-wall of the bottle, just above its base.

    • Make sure the hole is big enough for the thin stiff straw to go in; if not, make it big with scissors.

    • Cut the thin stiff straw in half.

    • Insert one piece of it through the hole.

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    • Place it in such a way that equal lengths of the straw should be inside and out of the bottle.

    • Use enough glue to seal the straw-cap interface

    • Leave it to dry for 5-10 min.

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    • Closing the straw-hole of the thin straw with your finger, fill the bottle with water.

    • Optionally, you can use coloured water for the flow to be more appealing.

    • Screw the cap that has the longer length of the straw into the bottle.

    • Notice that the straw is now dipped into the water

    • Remove your finger from the straw and let the water flow out.

    • Do this near a sink or outdoors or over a receptacle so that the water doesn't drain out on the floor

    • Place a coin at the point where the water is flowing out.

    • Observe it throughout the flow and you should see that the flow rate is constant, regardless of the water level inside the bottle!

    vishal: Photos?

    Procheta Mallik - Reply

    • Covering the thin stiff straw on the bottle with your finger, fill the bottle with water.

    • Now, invert the straw and screw the cap to the bottle such that the cap with the longer piece of the straw is outside the bottle.

    • The bottle should be filled in such a way that straw piece inside the bottle stays above the water level or near the top of the bottle.

    • Remove your finger from the straw and let the water flow out.

    • Immediately, place a coin at the point where the water is flowing out.

    • Observe the flow rate; does it change over time?

    • Note that you may merge the two "Play" Cases by creating a hole in the bottle caps that snugly fits the long stiff straw without the need of glue. This way, you can slide the straw up and down the bottle caps and observe the flow rate as you do so.

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    • In this simple video, you can see both the cases in action!

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    • Coin skids off the spot due to slippery surface.

    • If flow rate is too low, the height between the straw on the side-wall and the straw on the cap is not sufficient enough to induce a flow. Cut 2 cm of the longer straw and try again.

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Finish Line

Procheta Mallik

Member since: 05/02/2017

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