Students of physics define acceleration as the rate of change of velocity (or speed) with respect to time. Expressed mathematically, acceleration is the time derivative of speed or velocity.
In turn, the time derivative of acceleration is “jerk”. For further time derivatives after jerk, the words are, “snap”, “crackle” and “pop” for each successive derivative.
Force, another familiar concept of physics, is measured in units of mass times acceleration. Unlike velocity and acceleration, however, time derivatives for force have never been defined.
Now, biologists and biomedical engineers are proposing to define a new term, “yank”, for changes in force over time. Their ideas are published in the Journal of Experimental Biology.
The objective is to quantify something that our muscles and nerves can feel and respond to. Scientists who study sports often use the term “rate of force development”, a measure of explosive strength.
Also, scientists who study gait and balance in animals and humans often analyse how quickly forces on the body change. “Yank” could be useful in understanding spasticity, a common muscle impairment in multiple sclerosis, spinal cord injury, stroke and cerebral palsy.
Source: Emory University
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