Mechanical properties of solid bodies Demonstration

DEMONSTRATION FOR YOUNG MODULUS

Instructions for demo

Equipment: barbell of a given mass m, thread (for measuring circumference), tape-measure, electronic calculator.

Objective: To estimate the Young modulus of a human bicep – the muscle on the front part of the upper arm. To do this you will measure your bicep muscle before and after you lift a barbell of given mass. 

Procedure:

1.      Choose one student from your group.

2.      Measure the length of his or her bicep and the circumference of his or her arm. Use the picture below to help you.

Explanation: the bicep begins just a few centimeters below the shoulder and ends a few centimeters above the elbow joint. The circumference of the arm should be measured as shown in the second picture.

3.      Have the chosen student grab the barbell and do a dead-lift (hold your arm straight and lift the barbell vertically up without bending your arm).

4.      As the chosen student lifts the barbell and stands vertically, measure the length of his or her bicep again.

5.      Record your data in the table below.

6.      The formula used to calculate the Young modulus is

E =  · ,

where F is the force applied to the system (weight of barbell), A is the cross-sectional area of the bicep (approximately 1/3 of the cross-sectional area of the arm), Δl is the extension of the bicep and l is the initial length of the bicep (i.e. before the weight is lifted).

7.      Repeat this process for other members of your group.

8.      Compare the results and answer the following questions:

a)      On what quantities does the Young modulus depend (in general)?

b)      Was the Young modulus similar for different members of your group?  If there were any differences, what do you think might explain them?

c)