Comparing stress exerted by different running shoes
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Comparing stress exerted by different running shoes
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[post_date] => 2025-01-09 07:35:33
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[post_content] => Practice Passage (Question 1-5)
*This passage is the property of Khan Academy and has been reformatted into an AAMC-style interface in their entirety by MedLife Mastery. MedLife Mastery does not endorse and is not an affiliate of Khan Academy.
A team of scientists is attempting to develop a new type of running shoe that reduces the stress exerted on a runner’s body during high-intensity running. One important measurement that determines the amount of stress experienced by the body is vertical force exerted on the body during running---both the magnitude and the duration for which the body experiences this force influences the tissue fatigue experienced by runners.
As part of their efforts, they devise an experiment in which they ask subjects to run across a specialized scale that measures the vertical force acting on their body as a function of time. They ask four subjects to run for 7 steps across the scale while wearing each of three different types of shoes, resulting in a total of 12 time series consisting of four participants each testing three shoes. To simplify their data, for each time series they then average the 7 steps into a single “average” step. Then, for each of the three shoes tested, they average together the results of the four participants, resulting in a final experimental data set consisting of three curves showing the force versus time for a typical running step in each of the shoes. These curves are shown in Figure 1.
Figure 1: Comparison of force versus time for a single step in three different shoe types, averaged across multiple steps and test subjects.
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[question] => Which of the following forces best describes the force measured by the scientists?
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[description] => Reason for the Correct Answer:
Nuclear repulsion only acts over distances smaller than atoms.
Gravitational attraction acts downwards on the body, in the direction of the ground.
Electromagnetic repulsion is responsible for the normal force exerted upwards on the body by the ground.
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[each_answer] => A. Gravitational attraction
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[each_answer] => B. Electromagnetic attraction
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[each_answer] => C. Nuclear repulsion
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[1] => Array
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[quiz_unique_key] => 3873426850
[question] => Which of the following quantities affects the force acting on the runner’s bodies?
[value] => Array
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[answer] => 4
[description] => Reason for the Correct Answer:
During standing, the vertical force imparted by the ground is determining solely by an individual’s weight.
During running, additional force is used to propel the body forward.
Foot size affects the pressure exerted on the body, but not the total force.
The weight and intensity of running jointly determine the force acting on the runner’s body.
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[each_answer] => A. Weight
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[each_answer] => B. Intensity of running
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[each_answer] => C. Size of foot
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[each_answer] => D. I and II
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[2] => Array
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[quiz_unique_key] => 83407773
[question] => Which of the shoe designs imparts the greatest total impulse to the runner’s foot?
[value] => Array
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[answer] => 1
[description] => Reason for the Correct Answer:
Impulse is the force times the total time over which the force acts
This corresponds to the area under each of the curves
Shoe 1 has the most area under the curve and thus imparts the greatest impulse
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[each_answer] => A. Shoe 1
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[each_answer] => B. Shoe 2
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[each_answer] => C. Shoe 3
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[each_answer] => D. Cannot be determined without additional measurements
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[question] => Which of the following modifications would improve the scientist’s experiments?
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[answer] => 4
[description] => Reason for the Correct Answer:
The order of averaging does not affect the data.
The variation between steps from a single individual is likely smaller than the variation between steps from different individuals.
In the current data, it is possible that three of the test subjects saw no difference in the force versus time graph, while only one experienced a difference and skewed the average.
The scientists’ experiment would be better if they compared the four individuals separately without averaging their data.
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[each_answer] => A. The scientists chose the best method.
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[each_answer] => B. Compare each step separately without averaging them into one step.
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[each_answer] => C. Average the four participant’s results first, then average their steps.
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[each_answer] => D. Compare the four participants separately without averaging their data.
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[question] => Suppose the scientists accidentally purchase an identical scale that only records the pressure exerted on the scale as a function of time. Which of the following would they need to measure in order to generate data showing the same trend as in Figure 1?
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[answer] => 1
[description] => Reason for the Correct Answer:
The pressure and force experienced are independent of the type of material used in the show.
Pressure is defined as force divided by area.
The scientists should measure the area of the sole of each shoe in order to approximately convert their pressure data to force data.
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[each_answer] => A. Area of the sole
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[each_answer] => B. Length of the sole
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[each_answer] => C. Thickness of the sole
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[each_answer] => D. Material used to make the sole
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