In the previous unit on the Strength and Elasticity we learned that lifting and holding heavy objects places quite large force (and resulting stress) on the body, so moving patients puts Jolene at risk for injury. Jolene must assume that risk because even those forces are small compared to forces experienced when impacting a hard surface during a fall. Therefore, patient falls must be avoided.
- “Falls with serious injury are consistently among the Top 10 reported to The Joint Commission’s Sentinel Event database […] with the majority of these falls occurring in hospitals.
- Every year in the United States, hundreds of thousands of patients fall in
hospitals, with 30-50 percent resulting in injury.
- Injured patients require additional treatment and sometimes prolonged hospital
stays that increase medical costs by an average of $14,000.”
Impacts due to falls are not the only source of large forces. In fact, any situation involving a rapid change in motion will produce relatively large forces. These include car accidents, collisions between people, jumping, landing, and explosive body movements. As a result, medical professionals and first-responders often treat patients who experience mechanisms of injury (MOI) that involve rapid changes in motion as having spinal and/or internal injuries until confirmed otherwise by medical imaging or complete examination. Before we can analyze the forces associated with rapid changes in motion, we must also learn how to quantify motion itself. Falling provides an excellent place to begin the study of motion, so let’s start there.
Skydiving Free Fall
The time a skydiver spends between leaving the aircraft and opening a parachute is often called the “free fall” time. During a recreational skydive the “free fall” time is about one minute. The current record “free fall” time of about 5 minutes was set by Alan Eustace in 2014 when he fell from an altitude of more than 135,000 feet. According to the Paragon Space Development Corporation, “Eustace reached top of over 800 miles per hour. He was going so fast that his body broke the , creating a that could be heard on the ground.” The jump broke the previous record of 127,852 feet set by Felix Baumgartner in 2012. The 2012 jump was sponsored by GoPro cameras and the video has a much higher production value than the more recent 2014 jump:
Physics Free Fall
Now that we have introduced the skydiver’s use of the term free fall, we need to recognize that physics uses the term free fall in a completely different way, so we will need to be careful to avoid confusion. In physics, and in this book, we use the term to describe the motion of an object when is the only force acting on the object, or any other forces are small enough compared to gravity that we can ignore them without introducing too much error. Skydivers experience gravity and significant , so they are not actually in free fall.
- "Preventing falls and fall-related injuries in health care facilities" by Sentinel Event Alert, The Joint Commission ↵
- Majorkev at English Wikipedia [CC BY 3.0 (https://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons ↵
- "Skydive Miami" by By Norcal21jg, from Wikimedia Commons is in the Public Domain ↵
an unexpected occurrence involving death or serious physical or psychological injury, or the risk thereof. Serious injury specifically includes loss of limb or function.
distance traveled per unit time
sudden increase in aerodynamic drag and other undesirable effects experienced by an object when it approaches the speed of sound
the sound associated with the shock waves created whenever an object travelling through the air travels faster than the speed of sound
the motion experienced by an object when gravity is the only force acting on the object.
attraction between two objects due to their mass as described by Newton's Universal Law of Gravitation
a force acting opposite to the relative motion of any object moving with respect to a surrounding fluid