Options for Injury prevention
We have learned that some injuries result from large forces between body parts or on the body from other objects. Those are associated with large caused either by interaction with moving objects (cars, soccer balls) or large accelerations generated during . There are of course injuries caused by large forces in the absence of acceleration, such as crushing injuries, and those types of injuries can be analyzed using concepts of , , and . However, large accelerations are the hallmark of non-equilibrium injuries, such as those discussed in this unit. Therefore, we can prevent non-equilibrium injuries by:
- Increasing the of body tissues so that they can handle larger and thus larger force.
- Increasing the of body parts so that the remains below the tissue’s , even for larger forces.
- Decrease the size of , and thus forces and resulting , experienced by the body.
The first two options are controlled by genetics and regular exposure to large, but not injury inducing forces, also known as exercise. The next few chapters will focus on the third option, which is achieved by good choices, thoughtful movement, and technology.
Everyday Example: Headrest
The headrest in your car is not actually designed as a place to rest your head. Its real purpose is to prevent injury. If someone rear-ends your car it will accelerate forward. As a result your body is accelerated forward by and from the seat. Your head is also accelerated forward at the same rate by a normal force from the headrest, keeping your head above your shoulders and your neck in a safe position. If the head rest were not there, your head would momentarily remain in place due to as your body moved forward, then suddenly be pulled along with the body as the tissues of the neck became stressed (and strained). The lag in head position gives the impression that the head snapped back, but really the body moved forward. Your head does remain attached to your accelerating body, so the tissues in your neck suddenly experience a large stress as they provide the force required to accelerate the head and stress could cause injury. You can see the importance of the headrest in these crash-test videos:
The headrest doesn’t necessarily reduce the felt by the head as much as provide the force needed to accelerate the head along with the body, so that the neck doesn’t have to, thus reducing the forces between the head and neck.
- Carlson, K. J., & Marchi, D. (2014). Reconstructing Mobility. New York: Springer. doi:10.1007/978-1-4899-7460-0 ↵
any interaction that causes objects with mass to change speed and/or direction of motion, except when balanced by other forces. We experience forces as pushes and pulls.
the change in velocity per unit time, the slope of a velocity vs. time graph
movement or the ability to move from one place to another
a state of having no unbalanced forces or torques
a physical quantity that expresses the internal forces that neighboring particles of material exert on each other
the measure of the relative deformation of the material
the maximum stress a material can withstand
The cross-sectional area is the area of a two-dimensional shape that is obtained when a three-dimensional object - such as a cylinder - is sliced perpendicular to some specified axis at a point. For example, the cross-section of a cylinder - when sliced parallel to its base - is a circle
the outward force supplied by an object in response to being compressed from opposite directions, typically in reference to solid objects.
a force that acts on surfaces in opposition to sliding motion between the surfaces
the tenancy of an object to resist changes in motion