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1.6

Minor Versionm

by Vishal Bhatt

Introduction

Fix a shirt button in the centre of a card sheet. Pass a cotton thread through two holes of the button and knot the two ends to make a loop. This simple toy can spin at very high speed and hence, can be used to separate liquid mixtures. Manu Prakash, professor of bioengineering at Sanford University first demonstrated and perfected using this 'toy' for this purpose. It has opened a host of possibilities for the bio-medical field. Anybody with some paper and string can now centrifuge blood for blood tests without electricity and need for an expensive machine.

Video Overview

    • Take care while using scissors as well as the paper cutter, avoid making contact with their sharp edges and points.

    • Be careful while handling the capillary tube, it's made of glass and might create sharp edges when broken. Be sure to dispose of any excess glass pieces not useful to the experiment.

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  1. Start by inserting the pencil in the compass and measuring out 6cm.
    • Start by inserting the pencil in the compass and measuring out 6cm.

    • Cut a 14 cm x 14 cm piece of cardboard.

    • Now, being careful not to move the compass arms, use the pencil end to draw two diagonal lines on the cardboard square. The point where the diagonals meet is the centre of the square.

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    • Place the compass point on the centre and draw a circle. What do you think is the diameter of this circle?

    • Cut the circle out with the line as a guide.

    • Now place a button in the centre of the disc you've cut out and draw it's outline with the pencil.

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    • Push the scissor into the centre of the circle and rotate to scrape out a hole.

      • Be careful not to make the hole bigger than the button outline you made before. In fact, a hole slightly smaller than the outline is ideal. The card can deform slightly and allows you to squeeze the button in for a tight fit.

    • Apply a small amount of glue around the hole.

    • Push the button into the hole. Now let the glue dry for 5-10 mins before moving to the next step.

      • Make sure the holes on the button are not covered with glue. If they are, use a safety pin to clear the glue from the holes after the glue has dried.

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    • Insert one end of the string into one of the button holes.

      • If the string doesn't fit use a pin to push it into the hole.

    • Now take the thread on the other side of the button and insert it through the hole that's opposite to the first hole you inserted the thread through.

    • You should now have both ends of the string on one face of the paper disc.

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    • Tie the two ends together securely with a double knot.

    • Repeat the prosses to add one more thread through the other two holes in the button

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    • Add some fine soil to a small cup of water (say ~50ml). Stir well till the mixture is a uniform brown colour.

      • A darker brown colour is better because it will show a more dramatic seperation, this is because of the higher ratio of mud suspended in the water. This is also why fine mud is preferred, the smaller the individual particles of mud the more likely they are to remain suspended in the water.

    • Now dip the capillary tube or refill into the mixture. Submerge as much of the tube as possible, this will ensure that a good portion of the mixture ends up in the tube.

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    • Dip the vial into the mud water mixture.

    • Close the lid of the vial. There should now be a small amount of the mixture retained in the the vial.

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    • Place the sample as close to the edge of the fuge as possible and roughly at a 90° angle from any tangent on the circumference.

    • Now tape the sample in place with a length of clear tape. Use the the tape lengthwise along the sample and let ~2cm wrap around to the other side of the disc.

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    • You are now ready to separate the sample.

    • Run the fuge for about 2mins at a time and check the results.

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    • Sample after 2 minutes. Note a slight lightening of its brown tint.

    • Sample after 4 minutes. The colour lightens further.

    • Sample after 6 minutes. Sample is almost clear.

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    • The mud particles have clumped to the bottom.

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    • If the fuge wobbles too much after the sample is attached, mount an empty refill or capillary piece on the opposite side of the disc that the sample is on. This will serve to balance it.

    • While sealing the tube, take care not to tear the tape. If there is a hole or small gap in the tape seal, the mixture you are trying to separate will stream out when the fuge is being spun.

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    • Which end of the vial does the mud settle.

    • While the disk is spinning, try to change the orientation.

    • Instead of letting the vail sit in the center of the disk, place it on one of the sides.

    • How does the rotational speed and the amount of time affect the separation of the mud.

    • Fill only a fourth of the vial and perform the experiment without closing the lid of the vial. Which part of the mixture comes out first.

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    • An interesting variation to try would be to mount the button off center. Try changing its distance from the center as well.

    • Instead of a circle, make the centrifuge using a different shape; like a square, or an octagon

    • As an extra change in shape, you could also change the size of the centrifuges

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    • Cut a circle with the center marked

    • Cut a smaller circle and mark 4 diagonals. Make sure this circle is much smaller than other circle

    • Place the smaller circle at the center of the big circle and mark the ends of the diagonals with a sketch pen

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    • Using the compass to make holes at the markings

    • Pass the thread through the holes made. Make sure the holes are diagonally opposite each other

    • Play! If you want to make a variation of the variation, change the distance from the center to the holes.

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Finish Line

Kailash NR

Member since: 05/02/2017

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