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Guilherme Mazui

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What is the Difference Between Friction and Shear?

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Friction and shear are two mechanical forces that contribute to pressure ulcer formation and tissue damage. They are not the same, and each affects tissue differently when applied to the body. Here are the main differences between friction and shear:

  • Friction: This is the force of rubbing two surfaces against one another, such as skin being dragged across a coarse surface like bed linens. Friction wounds are usually visible and occur to the superficial layers of the skin. Friction also contributes to the coefficient of friction, which is the ratio of the force required to move an object along a surface to the force pressing the object down onto the surface. The higher the coefficient of friction, the more aggressively the two surfaces will adhere to each other.
  • Shear: This is a gravity force pushing down on a person's body with resistance between the person and the chair or bed. Shear is often described as an internal opposing motion of tissue and bone created when a patient is sitting up in bed or in a chair. Shear injury occurs beneath the skin in the fat and muscle tissue and is not visible at the skin level. The amount of pressure exerted, the coefficient of friction between the materials contacting each other, and the extent to which the body makes contact with the support surface can affect shear.

In summary, friction is the force of rubbing two surfaces against one another, resulting in visible wounds on the skin's surface. Shear, on the other hand, is a gravity force that pushes down on a person's body and causes internal tissue damage, beneath the skin.

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  • What is the Difference Between Friction and Shear?
  • Comparative Table: Friction vs Shear

    • Comparative Table: Friction vs Shear

    Friction and shear are mechanical forces that contribute to tissue injury, such as pressure ulcer formation. They are separate phenomena, but often work together to create tissue ischemia and ulcer development. Here is a table summarizing the differences between friction and shear:

    Feature Friction Shear
    Definition The mechanical force exerted when skin is dragged across a coarse surface, such as bed linens. The mechanical force that acts on an area of skin in a direction parallel to the skin's surface, affecting the deeper tissues.
    Injury Friction injury is visible and appears as an abrasion or rubbed skin. Shear injury is not visible at the skin level because it happens beneath the skin, causing ischemia and leading to cellular death.
    Resistance Friction opposes movement when two surfaces are in contact with each other. Shear stress is the force per unit area that causes the deformation of a material.
    Occurrence Friction wounds occur when an object is dragged or rubbed across the skin. Shearing wounds can be caused by elevating the head of the bed, increasing shear injury in the deep tissue.

    In summary, friction is the force that opposes movement between two contacting surfaces, resulting in visible injuries to the skin. Shear, on the other hand, is a force that acts on the skin parallel to its surface, affecting deeper tissues and causing hidden injuries beneath the skin.

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    Guilherme Mazui

    Guilherme Mazui is graduated in journalism from the Federal University of Minas Gerais (UFMG) and a master's degree in Communication from the University of São Paulo (USP). In addition, he has experience in advertising writing and has worked as a content editor in several companies.