Question

Back injuries are very common in humans and are often caused by lifting objects with the legs straight while leaning over; also known as “lifting with the back.” Use the concepts learned in this lab to explain why one should “lift with the legs” rather than with the back. Make sure to discuss the forces and torques involved, and how they differ in the two lifting techniques.

Answer 1

Using our back to lift would consist of a class 3 lever because the weight would be targeted at the far end and the back muscles would be closer to the center of mass. Lifting with our legs would be considered a class 2 lever, with the weight being targeted closer to the center of mass, Because a class 3 lever requires much more muscle force to counter the weight force, it wouldcause an easy strain on the back muscles. Since a class 2 lever requires less muscle force tocounter the force of weight, lifting with the legs would prove to be a more effective way to put less strain on the body muscles.

Results & Discussion : By completing this lab, we were able to see and examine how the human body relates to physics,specifically to static equilibrium. We could see in each part of this experiment how the muscles generate torque to maintain rotational equilibrium against the force of gravity and counters the force of weight in each circumstance. The human head proved to be a class I lever in that it showed how the neck muscles counterbalance the weight of the head. Standing on your tiptoes exemplified a class II lever because the weight acts downward while the calf muscle contracts to generate an upward force that counters the weight of the body. The bicep acted as a class 3 lever with a relatively large muscle force (and a “shoulder”) needed to counterbalance the force of weight. By doing this experiment we were able to understand the relationship between torque and static equilibrium, as well as their relation to the human body. The different lever types required different magnitudes of forces in order to maintain static equilibrium. Mostly all of our expected predictions held true through the results of the experiment. Any source of error in the results could be from calculation error or failure to establish an equilibrium prior to adding muscle and weight force.