Lecture #2 (Forces & Tissue Properties) Flashcards
What is the definition of force?
That which pushes or pulls through direct mechanical contact or through the force of gravity to alter the motion of an object.
What are internal forces?
Forces that act on various structures of the body (i.e. muscle forces)
What are external forces?
Forces that are outside the body (i.e. weight, gravity, air/water resistance, friction, other objects, etc.)
What type of quantity is force?
A vector
What does a vector force have? (3)
Magnitude
Direction
Point of application
True or false:
Gravity has a point of application.
False–gravity is a constant force, therefore it does not have a point of application.
What type of movement has no effort on the part of the subject involved, and the motion is completely due to an outside force?
Passive
What type of movement is produced by the subject’s own muscular activity?
Active
How it the human body designed to move? Why?
The human body is made for bursts of movement and sustained momentum rather than slow movements. This is because it takes less energy for us to do so.
What is the imaginary point representing the weight center of an object?
Center of gravity (COG)
Where is our COG?
Anterior to S2
True or false:
Males have a slightly lower center of gravity than women.
False
What is the imaginary vertical line that passes through the center of gravity (the action line and direction of force of gravity on a person)?
Line of gravity (LOG)
When does a person fall over?
When their line of gravity gets outside the base
What type of forces cause movement?
Unbalanced forces (if the forces were balanced, then no movement would happen because of a net force of 0)
What type of force occurs within the body? Outside the body?
Internal; external
What type of force is produced by muscular activity?
Internal
What is an example of a constant, external force?
Gravity
What is the magnitude of a force?
The amount of force being applied (the power behind the force)
What is weight? (formula)
Mass x acceleration due to gravity
True or false:
Muscles can create various magnitudes of force to create, halt, and control motion.
True (this is why kids can be uncoordinated)
How does force occur in the body?
In direct proportion to the number and size of fibers contracting in the muscle (typically measured in groups of muscles)
How do forces work in the body?
They go through a lever system (skeletal system)
How do you want your base of support?
As wide a possible
What is the point of application?
The point at which a force is applied to an object
Where does gravity have its point of application? For a muscle?
COG; the muscle’s attachment to a bony lever (point of intersection of the line of force and the mechanical axis of the bone)
Provide an example of a scenario in which there is multiple forces applied to the same object.
A punted ball (force of kick, gravity, and wind)
Quadriceps contracting
What are colinear forces?
Forces that are applied in a straight line with the result being the sum of the forces (a+b=c) or (a+ -b=c)
What are concurrent forces?
Forces that act at the same point of application at different angles
What are parallel forces?
Forces that are parallel to each other but not in the same action line.
True or false:
Everything provides a parallel force against gravity.
True
What is friction?
The force that opposes efforts to slide or roll one body over another
What does the amount of friction depend on?
The nature of the surfaces and the forces pressing them together
What is an example of an anatomical structure that helps to work against friction?
Bursa sacs
How does the force of friction work when compared to the object?
Parallel to surfaces and opposite to the direction of motion
True or false:
The force generated by muscle may be summated from one segment to another
True–this is how motion in sports happens (think of throwing as an example- the forces from legs is transferred to the trunk and so on)
What is the resolution of external forces?
It is accomplished in the same manner as muscular forces applied at an oblique angle (so we have to position ourselves to get the best possible use of force)
What is the force of gravity measured as the weight of the body applied through the COG of the body and directed towards the earth’s axis?
Weight
What is the ability to resist distorting influences and to return to the original size and shape?
Elasticity
In regards to elasticity of muscle, what acts to distort it and what is the distortion that occurs?
Stress=acts to distort
Strain=distortion that occurs
What type of force occurs when the direction of force is not in line with the object’s COG?
Rotary force
What is torque?
The force it takes to create rotation
What type of equilibrium occurs when an object is placed in such a way that an effort to disturb it would require it’s COG to be raised?
Stable (because it has a lower COG)
What type of equilibrium occurs when a slight disturbance will drop the subjects COG to a lower point?
Unstable (because it has a higher COG)
What type of equilibrium occurs when an object’s COG is neither raised nor lowered when it is disturbed?
Neutral
How is stability maintained?
When external forces = internal forces
What type of force causes stability? Instability?
Stability= internal forces Instability= external forces
What is the force that pulls and stretches tissue? WHat creates it?
Tension (what muscles create)
What is the force that pushes tissues together that may result in their crushing?
Compression
What is the force that moves across the parallel organization of tissue?
Shearing
What is the force that acts on a horizontal beam that places stress within the structure?
Bending
What is the force that causes an unaxial stress or twist of tissue?
Torsion
What types of forces are catastrophic in nature?
Shearing, bending, and torsion
What types of injuries do shear forces cause? (x6)
Spondylolisthesis Disc herniations SI joint pain Spiral fractures Meniscal/labral tears Blisters
True or false:
Our bodies are visoelastic and contain both viscous and elastic properties.
True
What is the yield point?
The point at which elasticity is almost exceeded
What does the stress/strain curve depict?
The stresses vs strain of a material (i.e. the amount of deformation that can occur)
Of the distinct regions of loading on the stress/strain curve, which is when the tissue stretches easily without much force? (Making the fibers go from wavy to straight)?
Toe region
Of the distinct regions of loading on the stress/strain curve, which is when there is continue stress added to the tissue–but more force is still needed to create further deformation?
Elastic region
Of the distinct regions of loading on the stress/strain curve, which is the transition from the elastic region to the plastic region?
Yield point
Of the distinct regions of loading on the stress/strain curve, which is when the load has resulted in a stretch beyond the tissue’s ability to return to pre-load length? (there are microscopic tears occuring here)
Plastic region
Of the distinct regions of loading on the stress/strain curve, which is when the load and rate have exceeded the mechanical properties of tissue?
Region of failure
What is the slope of the stress/strain curve?
Young’s modulus
What is the area under the stress/strain curve?
Toughness (resistance to force)
What occurs with low load, short duration?
Hysteresis
