PE 310 Chapter 3
Third-class lever functional design
Speed and range of motion (requires large force to move a relatively small resistance)
For us to control equilibrium and hence achieve balance, we need to maximize
Stability
Friction may be further categorized as
Static or kinetic
Mechanics is divided into:
Statics and dynamics
Forces that act individually or in combination to provide mechanical loading that may result in excessive tissue deformation
Tension (stretching or strain), compression, shear, bending, and torsion (twisting)
Balance
The ability to control equilibrium, either static or dynamic
Mass
The amount of matter in a body, affects the speed and acceleration in physical movements
What determines the type of lever and the application for which it is best suited?
The arrangement or location of three points in relation to one another
What are the three points that in relation to one another that determines which type of lever and which it is best suited?
The axis, the point of force application (usually the muscle insertion), and the point of resistance application (sometimes the center of gravity of the lever and sometimes the location of an external resistance)
A person has balance when the center of gravity falls within the ______
The base of support
Instantaneous center of rotation
The center of rotation at a specific instant in time during movement
Angular displacement
The change in location of a rotating body
The mechanical aspect of each component should be considered with respect to?
The component's machine-like function
Linear displacement
The distance a system moves in a straight line
Resistance arm
The distance between the axis and the point of resistance application
In musculoskeletal discussions the resistance arm may also be referred to as?
The external moment arm; applied externally
The perpendicular distance between the location of force application and the axis is known as?
The force arm, moment arm, or torque arm
Ground reaction force
The force of the surface reacting to the force placed on it, as in the reaction force between the body and the ground when running across a surface
Friction
The force that results from the resistance between the surfaces of two objects moving on each other
In musculoskeletal discussions the force arm may also be referred to as?
The internal moment arm; applied internally
Human movement occurs through:
The organized use of a system of levers
Center of gravity
The point at which all of the body's mass and weight are equally balanced or equally distributed in all directions
Center of rotation
The point or line around which all other points in the body move
Impulse
The product of force and time
Momentum
The quality of motion, which is equal to mass times veocity
Velocity
The rate at which an object changes its position, includes the direction and describes the rate of displacement
Acceleration
The rate of change in velocity
Coefficent of friction
The ratio of the force needed to overcome the friction to the force holding the surfaces together
Stability
The resistance to a change in the body's acceleration or, more appropriately, the resistance to a disturbance of the body's equilibrium
Inertia
The resistance to action or change
Rolling friction
The resistance to an object rolling across a surface
Kinetics
The study of forces associated with the motion of a body
Biomechanics
The study of mechanics as it relates to the functional and anatomical analysis of biological systems
Mechanics
The study of physical actions of forces, which can be subdivided into statics and dynamics
Generally, the center of gravity for humans is located in the vicinity of
The umbilicus
Most of the levers in the human body are:
Third-class levers, which requires a great deal of force to move even a small resistance
Human example of speed and range of motion in first-class lever
Triceps brachii in extending the elbow
A person has balance depending on the height of the center of gravity.
True
A person has balance depending on the weight (mass).
True
A person has balance depending on where the center of gravity is in relation to the base of supper
True
A person has balance in the direct proportion to the size of the base
True
A relatively smaller force may be applied to the wheel to move a relatively greater resistance applied to the axle
True
All tissues, in varying degrees, resist changes in their shape
True
As we utilize the musculoskeletal system to exert force on the body to move and to interact with the ground and other objects or people, significant mechanical loads are generated and absorbed by the tissues of the body
True
Balance is important for the resting body as well as for the moving body
True
Depending on the activity involved, we may desire increased or decreased friction
True
Equilibrium may be enhanced by increasing the friction between the body and the surface it contacts
True
Every additional rope connected to movable pulleys increases the mechanical advantage by 1
True
For movement to occur when either of the resistance components increases, there must be an increase in one or both of the force components
True
Force is the mass times acceleration (F= M X A)
True
Generally, balance is to be desired, but there are circumstances in which movement is improved when the body tends to be unbalanced
True
If the force and force arm remain constant, a greater resistance may be moved by shortening the resistance arm
True
If the radius of the wheel is greater than the radius of the axle, then the wheel has a mechanical advantage over the axle due to the longer force arm
True
In anticipation of an oncoming force, stability may be increased by enlarging the size of the base of support in the direction of the anticipated force
True
In joints of the body the axis is not usually fixed, due to their accessory motion
True
In statistics all forces acting on the body are in balance, resulting in the body being in equilibrium.
True
In the human body, the axis of rotation is provided by the various joints
True
Inertia is the tendency for the current state of motion to be maintained, whether the body segment is moving at a particular velocity or is motionless
True
Kinesthetic physiological functions contribute to balance
True
Machines convert smaller amounts of force exerted over a longer distance to larger amounts of force exerted over a shorter distance. This may be turned around so that a larger amount of force exerted over a shorter distance is converted to a smaller amount of force over a greater distance.
True
Motion cannot occur without a force, and the muscular system is the source of force in the human body
True
Muscles produce the force necessary to start motion, stop motion, accelerate motion, decelerate motion, or change the direction of motion
True
Necessary to study the body's mechanical characteristics & principles to understand its movements
True
Numerous weight machines utilize pulleys to alter the direction of the resistive force
True
Pulleys may be movable and can be combined to form compound pulleys to further increase the mechanical advantage
True
Rolling friction is always much less than static or kinetic friction
True
Rotation about an axis aids balance
True
Short force arms and long resistance arms require greater muscular strength to produce movement
True
Single pulleys have a fixed axle and function to change the effective direction of force application
True
Single pulleys have a mechanical advantage of 1
True
Static friction is always greater than kinetic friction
True
Static friction may be increased by increasing the normal or perpendicular forces pressing the two objects together, as by adding more weight to one object sitting on another object
True
Tension in tendons, connective tissues, ligaments, and joint capsules may passively generate internal forces
True
The amount of resistance can vary from maximal to minimal.
True
The balance is less if the center of gravity is near the edge of the base
True
The bones themselves or the weight of the body segment may be the only resistance applied
True
The greater the distance of the force arm, the more torque produced by the force
True
The greater the mass of an object, the greater its inertia
True
The greater the weight, the more balance
True
The larger the base of support, the more balance
True
The location of the exact center of rotation changes with changes in the joint angle
True
The longer the force arm, the less force required to move the lever if the resistance and resistance arm remain constant
True
The longer the lever, the more effective it is in imparting velocity
True
The lower the center of gravity, the more balance
True
The system of leverage in the human body is built for speed and range of motion at the expense of force
True
There is a proportional relationship between the force components and the resistance components
True
There is an inverse relationship between force and the force arm, just as there is between resistance and the resistance arm
True
To attain speed in moving the body, a strong muscular force is generally necessary
True
When either the wheel or axle turn, the other must turn as well
True
While the anatomical levers of the body cannot be changed, when the system is properly understood they can be used more efficiently to maximize the muscular efforts of the body
True
Without forces acting on object, there is no motion
True
A system in acceleration is unbalanced due to
Unequal forces acting on the body
To prevent injury injury or damage from tissue deformation
We must use the body to absorb energy from both internal and external forces
Second-class lever practical example
Wheel barrow, nut-cracker
Simple machines are the:
lever,pulley, wheel and axle, inclined plane, screw, and wedge
Static friction
the amount of friction between two objects that have not yet begun to move
Third-class lever arrangement
A-F-R; force between the axis and resistance
Second-class lever arrangement
A-R-F; resistance between axis and force
The Law of _______ states that a change in the acceleration of a body is directly proportional to the force causing it and inversely proportional to the mass of the body.
Acceleration
Second-class lever mechanical advantage
Always greater than 1
Third-class lever mechanical advantage
Always less than 1
Force magnitude
Amount of force usually expressed in newtons
in the body, joints represent what part of the lever?
Axes
Relationship to axis of balanced movements in first-class levers
Axis in the middle
Relationship to axis of speed and range in motion in first-class levers
Axis near force
Third-class lever relationship to axis
Axis near force
Relationship to axis of force motion in first-class levers
Axis near resistance
Second-class lever relationship to axis
Axis near resistance
The point in a joint about which a bone moves or turns to accomplish joint motion
Axis of rotation
First-class lever functional design
Balanced movements, speed and range of motion, and force motion
in the body bones represent what part of the lever?
Bars
Third-class lever human example
Biceps brachii and brachialis in flexing the elbow
To determine the amount of friction forces, we must consider
Both the forces pressing the two objects together and the coefficient of friction
How can we determine mechanical advantage?
By dividing the load by the effort
Stability may be enhanced by determining the body's ____________ and changing it appropriately
Center of gravity
Kinetic friction
Friction between two objects that are sliding along each other
In the lever system the point of rotation is known as the:
Fulcrum
The centers of the wheel and the axle both correspond to the
Fulcrum
Machines are used to increase or multiply the applied force in performing a task or to provide a ___________ ___________
Mechanical advantage
In terms of human movement, inertia refers to
Resistance to acceleration or deceleration
These mathematical quantities used to describe motion can be divided into what which two categories?
Scalars or vectors
Practical example of speed and range of motion in first-class levers
Scissors
Practical example of balanced movements in first-class levers
Seesaw
Third-class lever practical example
Shoveling dirt, catapult
A lever system with the force between the fulcrum and the resistance is best designed for:
Speed and range of motion
Mechanical advantage
-Load/effort or load divided by effort -Ideally using a relatively small force (or effort) to move a much greater resistance OR -Used to move one point of an object a relatively small distance to result in a relatively large amount of movement of another point of the same object
Machines function in four ways:
1. To balance multiple forces 2. To enhance force in an attempt to reduce the total force needed to overcome a resistance 3. To enhance range of motion and speed of movement so that resistance can be moved farther or faster than the applied force 4. To alter the resulting direction of the applied force
When the fulcrum is between the force and the resistance the lever system is known as a ____ class lever.
1st
F = 12, R = 30 What is the Mechanical Advantage?
2.5
When the resistance is between the force and the fulcrum, the lever system is known as a ____ class lever.
2nd
If the radius of the wheel is five times the radius of the axle, the wheel has a _______ to ________ mechanical advantage over the axle
5 to 1
The three type of machines in the musculoskeletal system involves:
A balancing of rotational forces about an axis
Law of inertia
A body in motion tends to remain in motion at the same speed in a straight line unless acted on by a force; a body at rest tends to remain at rest unless acted on by a force
Law of acceleration
A change in the acceleration of a body occurs in the same direction as the force that caused it. The change in acceleration is directly proportional to the force causing it and inversely proportional to the mass of the body
Displacement
A change in the position or location of an object from its original point of reference
What class of lever is it when the axis (A) is placed anywhere between the force (F) and the resistance (R)?
A first-class lever
Eccentric force
A force that is applied off center or in a direction not in line with the center of rotation of an object with a fixed axis
A wheel and an axle essentially function as
A form of first-class lever
What is commonly referred to as increasing our leverage?
A frequent practical application of torque and levers occurs when we purposely increase the force arm length in order to increase the torque so that we can more easily move a relatively large resistance
The axis is the point of rotation about which:
A lever moves
Which lever is it when the resistance (R) is somewhere between the axis (A) and the force (F)?
A second-class lever
Which lever is it when the force (F) is placed somewhere between the axis (A) and the resistance (R)?
A third-class lever
Kinematics
Concerned with the description of motion and includes consideration of time, displacement, velocity, acceleration, and space factors of a system's motion
In the body, muscles do what in regards to levers?
Contract to apply the force
Practical example of force motion in first-class levers
Crow bar
In order for rotation to occur in objects without a fixed axis, what must be applied?
Eccentric force
Wheels and axles are used primarily to
Enhance range of motion & speed of movement in the musculoskeletal system
Mechanical advantage of balanced movements in first-class levers
Equal to 1
Human example of balanced movements in first-class lever
Erector spinae extending the head on cervical spine
First-class lever arrangement
F-A-R; axis between force and resistance
Law of reaction
For every action there is an opposite and equal reaction
The mass of a body segment or the entire body times the speed of acceleration determines the
Force
The lever rotates about the axis as a result of?
Force (sometimes referred to as effort) being applied to it to cause its movement against resistance (sometimes referred to as load or weight)
Both the radius of the wheel and the radius of the axle correspond to the
Force arms
Second-class lever functional design
Force motion (large resistance can be moved with relatively small force)
A lever system with the resistance between the force and the fulcrum is best designed for:
Force movements
Our anatomical leverage system can be used to:
Gain a mechanical advantage that will improve simple or complex physical movements
Second-class lever human example
Gastrosnemius and soleus in plantar flexing the foot to raise the body on the toes
Mechanical advantage of force motion in first-class levers
Greater than 1
Speed
How fast an object is moving, or the distance an object travels in a specific amount of time
Static equilibrium
If the body is at rest or completely motionless
Momentum may be altered by
Impulse
The greater the momentum, the greater the resistance to change in the
Inertia or state of motion
Only muscles can actively generate ____________ force
Internal
Angular motion
Involves rotation around an axis; also known as rotary motion
Dynamics
Involves the study of systems in motion with acceleration
Statistics
Involves the study of systems that are in a constant state of motion, whether at rest with no motion or moving at a constant velocity without acceleration
What are the additional components of biomechanical study?
Kinematics and kinetics
Mechanical advantage of speed and range of motion in first-class levers
Less than 1
A rigid bar that turns about an axis of rotation or fulcrum
Lever
A rigid bar that turns about an axis of rotation, or fulcrum
Lever
What is the most common form of simple machine found in the human body?
Lever
The arrangement of the musculoskeletal system provides three types of machines in producing movement:
Levers, wheel/axles, and pulleys
Two types of motion
Linear motion and angular motion
Scalar quantities
Mathematical quantities are described by a magnitude (or numerical value) alone such as speed, length, area, volume, mass, time, density, temperature, pressure, energy, work, and power
Vector quantities
Mathematical quantity described by both a magnitude and a direction such as velocity, acceleration, direction, displacement, force, drag, momentum, lift, weight, and thrust
Curvilinear motion
Motion along a curved line
Linear motion
Motion along a line; also referred to as translatory motion
Rectilinear motion
Motion along a straight line
Forces either push or pull on an object in an attempt to affect
Motion or shape
Torque
Movement of force, is the turning effect of an eccentric force
The amount of torque can be determined by:
Multiplying the force magnitude (amount of force) by the force arm
What is the main source of force that produces or changes movement of a body segment, the entire body, or an object thrown, struck, or stopped
Muscles
Can the anatomical levers in the body be changed?
No
Dynamic equilibrium
Occurs when all the applied and inertial forces acting on the moving body are in balance, resulting in movement with unchanging speed or direction
External forces are produced from
Outside the body and originate from gravity, inertia, or direct contact
Distance
Path of movement and is the sum length it is measured to have traveled
Force arm
Perpendicular distance between location of force application and axis. The shortest distance from the axis of rotation to the line of action of the force. Also known as the moment arm or torque arm.
A first-class levers are designed to:
Produce balanced movements when the axis is midway between the force and resistance
A second-class levers are designed to:
Produce force movements, since a large resistance can be moved by a relatively small force
Third-class levers are designed to:
Produce speed and range of motion
Mechanical advantage equation, when it is always less than 1
Radius of the axle __________________________ Radius of the wheel
Mechanical advantage equation, when it is always more than 1
Radius of the wheel ____________________________ Radius of the axle
Equilibrium
Refers to a state of zero acceleration, where there is no change in the speed or direction of the body. May be either static or dynamic.
Third-class lever direction of force versus resistance
Resistance and force applied in opposite directions
Second-class lever direction of force versus resistance
Resistance and force are applied in opposite directions
First-class lever direction of force versus resistance
Resistance and force are applied in same direction
First-class lever arm movement
Resistance arm and force arm move in opposite directions
Second-class arm movement
Resistance arm and force arm move in the same direction
Third-class lever arm movement
Resistance arm and force arm move in the same direction
