Fracture Energy of Chicken Bones:
A Kinetics Approach
WA5
Aims/Objective & Hypothesis(es):
The purpose of this experiment is to use energy calculations in
quantifying the energy absorbed by surrogate popsicle sticks and
chicken bones upon fracture by an impact pendulum apparatus
starting at different initial angles, and therefore traveling at different
speeds before fracture. Such an investigation provides important
information in estimating the risk of bone fractures as a result of a
direct impact at various speeds. The central hypothesis of this lab is
that the speed of the pendulum immediately prior to impact will not
influence the fracture energy of the surrogate popsicle sticks and the
fracture energy of bone samples.
University of Pennsylvania
Department of Bioengineering
Methods, Protocol & Equipment:
Protocol
•Calibrate pendulum, calculate center of mass (statically and geometrically)
and moment of inertia (geometrically)
•Run popsicle stick surrogate and chicken bone trials at 10,000 Hz at two
different initial angles (90° & 120°) and plot rotational kinetic energy,
gravitational potential energy, and total energy of the system vs. time.
•Identify pre/post impact total energy (E), examine energy loss due to
friction, and determine Eabsorbed of surrogates and bones at both angles.
•Perform two tailed t-test, assuming equal variance, to determine if there is
a significant difference between two angle data sets.
Equipment
•Impact pendulum apparatus with rotational potentiometer
•Biopac data acquisition software and Excel
•Wood popsicle stick surrogates and 12 chicken bone samples
•Ruler, knife, cutting board, spring balance, protractor
University of Pennsylvania
Department of Bioengineering
Proposed Results/Findings/Deliverables:
•A plot of the system’s rotational kinetic energy, gravitational potential
energy and total energy vs. time.
•Absorption energies of fracture for surrogate and chicken bone samples
at two different impact speeds.
•Amount of energy absorbed by popsicle and chicken bones upon
fracture is independent of speed of the pendulum during impact as
determined by a two-tailed t-test assuming equal variance.
Potential Pitfalls:
• Somewhat inconsistent quantitative establishment of pre/post impact
points on system total energy vs. time plot.
• Frictional plot noise.
• Inaccurate Calculation of center of mass and moment of inertia due to
incomplete diagram in lab manual.
•Variance between individual bone samples.
University of Pennsylvania
Department of Bioengineering
Materials and Budget & Justification:
12 Perdue chicken drumsticks, costing $6.58, qualitatively similar in
size and shape. (each 6-ct pack ~1.5lbs costs $3.29)
Frequency of 10,000 Hz used because, while the potentiometer has a
maximum recording frequency of 20 Hz, the Biopac software is limited
in precision (~0.0048°). Through analysis of plots at various
frequencies, 10 Hz appears to maximize the frequency of the
potentiometer and precision of the Biopac software.
Angles of 135 degrees and 90 degrees used because they are both
large enough to guarantee fracture of the bone.
Slope function in Excel used to calculate rotational velocity of
pendulum. Average of 5 points yielded smoothest plot.
University of Pennsylvania
Department of Bioengineering