Chapter 8 (Basic Biomechanics) Flashcards
What does biomechanics involve?
Taking the principles and methods of machines and applying them to structure/function of the human body
Factors associated with non-moving systems
Statics
Factors associated with moving systems
Can be divided into kinetics, kinematics
Dynamics
Deals with forces causing movement in a system
Kinetics
What does kinematics deal with ?
Deals with forces involved in time, space, and mass aspects of moving system.
(Osteokinematics + arthrokinematics)
What is osteokinematics?
Deals with the manner in which bones move in space.
Without regard to the movement of joint surfaces
What is arthrokinematics?
Deals with the manner in which adjoining joint surfaces move in relation to each other
(In the same or opposite direction)
What is force?
Any action or influence that moves an object
The amount of matter that the body contains
Mass
The property of matter that causes it to resist any change of its motion in either speed or direction
(Mass is a measure of inertia)
Inertia
What is torque?
the tendency of force to produce rotation about an axis
Force developed by 2 surfaces
- Tends to prevent motion of one surface across another
Friction
What are the 3 laws of motion?
- Law of Inertia
- Law of Acceleration
- Law of Action-reaction
Which law is this:
An object at rest tends to stay at rest, and an object in motion tends to stay in motion
Law of Inertia
Ex. Arm will not bend without the force of the muscle
Describe the law of Acceleration
- the amount of acceleration depends on the strength of the force applied on an object
Ex. Kick 2 balls same size; the harder kick will go further - Acceleration is inversely proportional to the mass of an object
Ex. Kick 2 balls w/ same amount of force; ball w/greater mass will not travel as far
Describe the law of Action-Reaction
For every action there is an equal and opposite reaction
Ex. As you jump down on a trampoline, the trampoline pushes back with the same amount of force
What is needed to create force?
One object must act on another
What are the 3 characteristics of force?
- Magnitude
- Direction
- Point of application
When two or more forces are acting along the same line or plane.
Linear force
Ex. *pulling a boat
*Pushing a bed on same side
*2 people on opposite sides of a bed, pushing w/same force = no motion
Occur in the same plane and direction with a counter force in the middle but in the opposite direction
Parallel forces
Ex. seesaw
Describe a resultant force
Net effect of 2 divergent forces
Lies somewhere in-between
Occurs when two or more forces act in different directions, resulting in a turning effect
Force couple
What is an ex. of force couple?
Unscrewing a jar lid
Force A= fingers
Force B= thumb
What is torque ?
Moment of force; ability of force to produce rotation about an axis
Amount of torque lever depends on what?
- Amount of force exerted
2. Distance from the axis
What is an ex. of a torque lever?
Wrench- to increase torque
- Increase force applied to handle - Increase length of the handle
T/F
Torque is greatest when the angle of pull is 90 degrees
True
T/F
The longer the moment arm the more force you can generate
True
The perpendicular distance between the muscle’s line of pull and the center of the joint is the ____?
Moment arm
What are examples of torque in the bicep?
A. Elbow 90° - greatest torque
B. Elbow extended - little torque
C. Elbow flexed - less torque
when flexed or extended the moment arm shrinks. so less force
Torque with and without a patella
- With; it increases the angular force of the quadriceps muscle and allows the muscle to have a greater angular force
- Without; the movement arm is shorter and there is not as much force
When an object is balance, all forces acting on it are even
State of equilibrium
Mutual attraction between the earth and object
Gravity
What is the center of gravity (COG)?
Balance point of an object at which weight on all sides is equal
-Point at which the planes of the body intersect
What is base of support?
-That part of a body that is in contact with the supporting surface
-the surface of the body in contact with the ground
Ex. feet together = less stable
feet apart = more stable
What are simple machines?
- Lever
- Pulley
- Wheel and axle
- Inclined plane
What are some common lever terms ?
lever, axis, force, resistance, force arm, Resistance arm
What is a lever?
rigid bar that can rotate about a fixed point when force is applied to overcome resistance
Point about which a lever rotates
Axis
Causes a lever to move, muscle
Force
What is a the resistance, force arm, and resistance arm? (lever terms)
Resistance= weight of part being moved
Force arm= distance between the force and the axis
Resistance arm= distance between the resistance and the axis
- Which takes less energy?
- Holding a box 2” from your body or 10” from your body?
Holding a box 2” from body
Summarize mechanical advantage
-Less force is required if you put the resistance as close to the axis as possible and apply the force as far from the axis as possible
What is a pulley and its purpose?
-it is a grooved wheel that turns on an axle with a rope or cable riding in the groove
-the purpose is to change the direction of
a force OR the magnitude
of the force
What is a wheel and axle?
- Less common type of simple machine. [Lever in disguise]
- Consists of a wheel (or crank) attached to and turning together with an axle
- Used to increase force exerted
- Turning a large wheel requires less force than a small axle
What is an example of a wheel and axle?
-faucet handle
Handle = wheel
Stem = axle
-Turning on/off requires a certain amount of force. If the handle is removed, turning the axle requires greater strength. The larger the wheel the easier to turn.
Clinical application of the wheel and axle/shoulder
-Passive shoulder rotation
-Looking down from a superior view
Shoulder joint = axle
Forearm = wheel
-With elbow flexed, the wheel is much longer than the axle; Easier to turn
The relationship of force on an inclined plane
A. Longer ramp, less force, greater distance
B. Shorter ramp, more force, shorter distance
-What is gained in force is lost in distance
