Jim Szeszol Mendel Catholic High School
250 East 111 Street
Chicago, IL 60628
To study the effects of friction in a simple mechanical system.
1) Self propelled dynamics cart (coil spring driven)
2) Meter stick
1) Perform "Hookes Law" experiment for coil spring constant
2) Determine distance and time for PE transfer
3) Calculate KE transfer for
a) Translational KE
b) Rotational KE - wheels, pulleys, axles
4) Determine the efficiency of the system
Calculations : Determine the difference in energy levels using KE formulas
for energy of translation and rotation. The ratio of kinetic energy of the cart
to the potential energy of the spring will yield an efficiency value for the
Conclusion : In most first year physics courses energy lost to friction is
traditionally ignored. Through this activity the observation can be made that a
significant (80% - 90%) of the system energy is lost to frictional forces while
doing useful work.
Extensions / Modifications :
For translational KE only keep the ratio of rotational mass to translational
example - small wheels - light wheels - single pulley - added mass to cart.
For non-uniform motion - the cart will accelerate at rates dependent on the
coil spring constant and the selected step pulley. To study these rates a timer
tape can be attached to the cart to determine varying rates of motion.
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