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The aim of this experiment is to test whether or not a Crunchie bar could be used as a bone replacement.

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Wendy Croft 12NB

Crunchie Bones?

        The aim of this experiment is to test whether or not a Crunchie bar could be used as a bone replacement. If this were possible the crunchie would have to be strong enough to support the patients life style. The Crunchie bar will be used to replace a leg bone. After the experiment I will calculate the ultimate breaking stress of the Crunchie and then compare this to the ultimate breaking stress of a leg bone. I will calculate the stress by using the formula:

The apparatus is going to be set up as follows:

I will tighten both of the G-clamps by 90  at the same time, then I will read off the force on the dial of the scales. I will read the dial from directly above otherwise parallax may occur. I am using three crunchies at the same time, as this will be more reliable. To make

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By doing the following calculations I will determine the ultimate breaking stress of the crunchie bars for one leg.

Stress (     ) = force (f)  

                  Area (A)

Stress (     ) = 1190.0 N

                0.0105 m

Stress (     ) = 113333.3 Pa

       = 11 x 10    Pa

Due to inaccuracies of the scales I am going to calculate the maximum and minimum values of the force and then calculate the breaking stress due to these differences.

Maximum force = 1200 N

Minimum force =  1180 N

Maximum Stress = 1200 N


    = 114285.7 Pa  (1dp)

                    = 1.14 x 10   Pa

Minimum Stress = 1180 N


                 = 112380.9 Pa (1dp)

                 = 1.12 x 10  Pa

I have accounted for the inaccuracies of the scales and of the turning of the G-clamps by drawing error boxes on the graph. The size of the error boxes is 20N x 36  .

        Further calculations will determine whether or not the crunchie bar would be a suitable replacement for a leg bone.

Average mass of human = 60kg

Weight = mass x gravity

         = 60 x 9.8

         = 588 N

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Area of both legs = 60 x 10  m                Area of crunchies = 0.0105m

Calculations for bone:                             Man lands on two legs = 0.0105 x 2

Stress = F                                                                          = 0.021m


  Stress =  F

         =  3.80 x 10    N                                                                A

                     60 x 10    m                                                 = 3.80 x 10   N

         =  6.3 x 10   Pa                                                        0.021m

                                                                        = 18095238.1 Pa

                                                                 = 1.8 x 10   Pa

These calculations show that the crunchie bar could not with stand the stress when the patient moved. This is shown in the calculations because the value of stress on the crunchie bars when put in this situation is greater than that of the leg bones. Therefore the crunchie bars would break.

        Overall this experiment has shown that a crunchie bar could not be used as a suitable bone replacement as it would not be able to with stand the ultimate breaking stress of a person if they were standing still or if the person was moving.

If I had more time to continue this experiment I would make a piece of apparatus, like a protractor, that enabled me to measure the degree turns that I made when turning the G-clamps making my measurements more accurate. Using the apparatus I could also make more turns such as 45   turns as well as 90   turns.

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