Editing 2539: Flinch

[[Cueball]] is performing [https://youtu.be/4a0FbQdH3dY?t=1518 a common physics demonstration] in which a heavy ball is hung from a rope or cable. The demonstrator, or a volunteer, pulls the ball back until it's close to their face (possibly even touching it), then releases it, allowing it to swing, and then return. Due to conservation of energy, the ball cannot return any further than its original release point, making it impossible for the person to be struck by it. Because a heavy pendulum will tend to lose little energy on each swing (relative to its overall energy), it will come back very close to its original point, so the experiment creates a conflict between the instinctive desire to escape a heavy object flying at your face, and the theoretical knowledge that it won't harm you.  

[[Ponytail]], an engineer, replies that she doesn't trust Cueball to have hung the pendulum correctly.  Engineers are trained in science, but work with practical applications, and tend to be very aware that practice is rarely as simple as scientific theories might imply. Even if the physical laws are constant, the experiment might not go according to plan. For example, if the cable were to snap or come loose while swinging toward the subject, the ball could strike them in the body, or land on their feet.  If the cable is more elastic than anticipated, it could stretch unpredictably, once again striking someone.  If the anchor point is not stable, it could shift during the experiment, once again causing harm. Also if the ball is not released but pushed, or if the one releasing it leans forward after release they might get hit in the face.

The title text shows a pre-med student's response. {{w|Pre-medical}} university courses have a reputation for being more intense and demanding than other undergraduate degrees, so the student is portrayed as being very stressed and time-conscious; showing little interest in the experiment itself, only in how it impacts their degree. In addition, medical students are commonly the subject of "interesting" medical experiments which may lead to long-term psychological and physical side-effects.

The student first asks if participating in the demonstration will count for a physics credit, implying that they're not willing to spend time on it unless it contributes to their academic requirements. They then ask if they can shorten the string to make the demonstration go faster. Shortening a pendulum does, indeed, cause it to swing faster, but the time saved would be less than the time necessary to make the modification, so the demonstration would not end sooner. Finally, they ask to do a variant where they ''deliberately'' get struck in the face, because they have a "thing for first aid training" immediately after. This would likely injure them, but the student is apparently willing to sacrifice their own safety and well-being in service to their academic career. It's not clear how this would help, although it could potentially help ''others'' learn first aid by having them practice on the new injury.

 

Various alternate takes on this experiment have been previously featured in [[755: Interdisciplinary]] and [[1670: Laws of Physics]], but this is the first time experiment is performed in a proper manner.