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by Procheta Mallik

Introduction

Hang a bucket from a secure hook or door knob with different types of fibres, and keep filling the bucket with water till the string breaks. Record your values for each type of fibre.

    • Make sure to keep the bucket only a few inches away from the ground, so that it doesn't drop and spill.

    • Be cautious with the scissors.

    • Stay a little distance away from the bucket, to be sure that it doesn't fall on your feet.

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  1. Cut each fibre into a piece of about 20 - 25cm in length.
    • Cut each fibre into a piece of about 20 - 25cm in length.

      • Satin Ribbon

      • Cotton Thread

      • Woollen Thread

      • Synthetic Fibre

    • Find a knob much like this one - the main purpose is to be able to hang a bucket off it.

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    • Start with one of the fibres (here we started with the cotton one), and tie two knots to the door knob as shown.

    • If you think the thread is still not secure to the knob, tie another knot.

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    • Place the other end of the thread at the handle of the bucket, and pull it through until the bucket is hanging off the ground.

    • If you find this hard, you can tie the thread to the bucket first and then to the door knob.

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    • Tie the knot securely and let the bucket dangle from the knob.

    • The bucket should be off the ground by a couple of inches as shown.

    • The weight of this bucket is around 1kg, so right now there is a 1kg mass hanging from the thread.

    • If it is too close to the ground, this could be a problem as the thread stretches first before breaking and if the bucket touches the ground during this phase - it would no longer break!

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    • Now we need a container to add water to the bucket, something like this cup as it will be easy to fill water in it.

    • We can check the volume of the cup, by seeing how many cups it takes to fit the 750ml of water that fills the plastic bottle.

    • Water in 750ml bottle fit in 2.25cups, so 1cup = 750ml/2.25 = 333.33ml. So 3 cups of water = 1L!

    • Note that 1L of water weighs 1kg.

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    • Add water to the bucket cup by cup. And after every three cups (1kg), mark where the bucket is hanging on the door.

    • Keep adding water and making marks until the the thread breaks and the bucket falls!

    • Make sure to count how many kgs you've added in total!

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    • Repeat the same procedure with the other three fibres and test their strength!

    • You can use a plastic bottle like the one shown in the pictures (find a 500ml or 1L plastic water bottle) or any other bottle as long as you know the measurement, if you don't want to use a cup.

      • But filling a plastic bottle would take much longer than filling a cup.

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    • For a reference point, these were the tested tensile strengths of each fibre during our experimentation:

      • Woollen thread: 1.5 - 1.75kg

      • Cotton Thread: 7 - 7.5kg

      • Synthetic Thread: 2 - 2.5kg

      • Satin Ribbon: was able to hold more than 10kg

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    • Make a table similar to this and fill it in with your values.

    • Circle the stretch length for the half way breaking point mark, and right before breaking point like shown for the cotton thread!

    • These values are only a sample, they might not coincide with your readings so don't worry, and don't use the stretch lengths as a reference point!

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    • If the thread breaks before adding any water at all, measure the weight of the bucket itself.

    • If the knot unwinds before the thread breaks, perform the experiment again with a more secure knot.

    • If you do not have a door knob like this one, find any other place or hook to hang a bucket.

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    • How is 1L of water equal to 1kg?

    • Which fibre has the highest tensile strength and why?

    • Which fibre has the lowest tensile strength and why?

    • Were your measurements close to the reference ones? If not, why?

    • Were you able to see any stretching of the thread (indicated by the pencil lines on the door) before the breaking point? Was it at equal intervals? Did you observe this stretching for all the fibres?

    • Try some variations with time! See if leaving the bucket with less water than its breaking point for some time breaks the thread eventually. How much less water does this work for? After how long does the thread break?

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Suchitha Vishwa

Member since: 05/02/2017

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