Unit 5: Strength and Elasticity of the Body
Moving patients is a routine part of Jolene’s work as a MED floor RN, but in reality there is nothing routine about the biomechanics of lifting and transferring patients. In fact, “disabling back injury and back pain affect 38% of nursing staff” and healthcare makes up the majority of positions in the top ten ranking for risk of back injury, primarily due to moving patients. Spinal load measurements indicated that all of the routine and familiar patient handling tasks tested placed the nurse in a high risk category, even when working with a patient that “[had a mass of] only 49.5 kg and was alert, oriented, and cooperative—not an average patient.”[1]. In this unit and the associated lab we will analyze forces within the body and examine how body tissues respond to those forces. This unit will introduce the concepts required, static equilibrium, lever classes, mechanical advantage, range of motion, stress, strain, elastic modulus, and Hooke’s Law. The learner outcomes for this unit are listed just below and below those are some key terms and concepts to look out for.
Learner Outcomes
- Identify classes of levers and explain advantages and disadvantages of each in terms of mechanical advantage and range of motion.[2]
- Apply lever and static equilibrium concepts to solve for forces and calculate mechanical advantage. [3]
- Identify and define the features of a stress-strain curve, including stress, strain, elastic region, elastic modulus, elastic limit, plastic region, ultimate strength, and fracture/rupture.[2]
- Apply Hooke’s Law along with the definitions of stress, strain, and elastic modulus to calculate the deformations of structures. [3]
Key Takeaways
Lever Arm
Effort Arm
Resistance (Load) Arm
Mechanical Advantage
Range of Motion
Elastic Modulus
Ultimate Strength
Linear Region
Elastic Limit
Plastic Region
Yield Point
Brittle
Ductile
referring to a lever system, the force applied in order to hold or lift the load
the force working against the rotation of a lever that would be caused by the effort
the point on which a lever rests or is supported and on which it pivots
the central point, pin, or shaft on which a mechanism turns or oscillates
There are three types or classes of levers, according to where the load and effort are located with respect to the fulcrum
the force that is provided by an object in response to being pulled tight by forces acting from opposite ends, typically in reference to a rope, cable or wire
reduction in size caused by application of compressive forces (opposing forces applied inward to the object).
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 range of values for stress and strain values over which a material returns to its original shape after deformation
