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