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by Procheta Mallik


Mount a spoke bent in the shape of a square wave inside a 1 litre plastic bottle, such that the two ends rotate. Attach a straw to one of the crests, create a circular motion on the spoke which will lead to linear motion on the straw.

    • Exercise caution while handling scissors/cutters.

  1. Make diametrically opposite holes about two-thirds of the way up the bottle
    • Make diametrically opposite holes about two-thirds of the way up the bottle

    • Insert scissors into one of the holes and make a cut along the length of the bottle

    • The length of the cut should not be less than 15 cm.

    • Bend the wire 4 cm from one of the ends. This is the first bend.

    • All the bends should be 90 degrees and should lie on a single plane.

    • The second bend in the wire should be approximately 2 cm away from the first bend.

    • Make sure the ends of the wire are are in opposite directions after making the second bend

    • Make the third bend at a distance of 1cm from the previous bend

    • All the bends should lie in the same plane.

    • Now at a distance of 2 cm from the preceding bend, bend the wire once again to form a U - shape.

    • Make another bend in the wire 4 cm away from the previous bend.

    • Make the last bend at a distance of 3 cm from the preceding bend. This is your handle.

    • Insert the wire through the straw about 2 cm from one end of the straw

    • Make sure the straw is placed within the U - shape of the handle.

    • Insert the handle and straw through the cut slit of the bottle

    • The straw should come out through the cap end of the bottle

    • Make hole in the centre of the cap with diameter more than that of the straw.

    • Put the cap on the bottle and let the straw come out through the hole.

    • Start rotating the handle and observe the translation of motion from the rotational motion of the handle to the linear motion of the straw.

    • Stick any figure or object at the end of the straw. Enjoy!

    • Not able to insert or take out the wire and straw into/from the bottle. Slit made from one side is too short.

    • Handle coming out or falling down through the slit. Stick tape on two sides of the handle inserted through the hole.

    • If the bends are too long, compared to the radius of the bottle, the crank may not rotate in the bottle freely.

    • What type of motion conversion is taking place in the crank?

    • Can you think of applications for this kind of translation of motion?

    • Is it possible to convert the straight/linear motion into circular/rotational motion also? Have you come across any machine(s) in daily life which work on such a principle?

    • Instead of rotating handle with hand, attach a fan to the handle. Blow on the fan to rotate the handle.

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Suhail Ahanger

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