Chapter 3 Kinesiology

Machine functions

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

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. acc= change in velocity

Equation for wheels and axles

Both the radius of the wheel and the radius of the axle correspond to the force arms. If the radius of the wheel is greater than the radius of the axle, then the wheel has a mechanical advantage over the axle so a smaller force may be applied to the wheel to move a greater resistance applied to the axle. MA= radius of the wheel/radius of the axle

Stability

For us to control equilibrium and hence achieve balance, we need to maximize stability. Stability is the resistance to a change in the body's acceleration or, more appropriately, the resistance to a disturbance of the body's equilibrium.

Eccentric force

Force that is applied in a direction not in line with the center of rotation of an object with a fixed axis. In objects without a fixed axis, it is an applied force that is not in line with the object's center of gravity.

equilibrium

In relation to human movement, equilibrium refers to a state of zero acceleration, where there is no change in the speed or direction of the body. Equilibrium may be either static (body motionless) or dynamic (all the applied and inertial forces acting on the moving body are in balance, resulting in movement with unchanging speed or distance)

Kinematics

Kinematics is concerned with the description of motion and includes consideration of time, displacement, velocity, acceleration, and space factors of a system's motion

Kinetics

Kinetics is the study of forces associated with the motion of a body.

Forces in the body

Muscles are the main source of force that produces or changes movement of a body segment, either push or pull on an object in an attempt to affect motion or shape F=ma

Pulleys

Single pulleys have a fixed axle and function to change the effective direction of force application. Single pulleys have a mechanical advantage of 1

Tension

Tension (stretching or strain), compression, shear, bending, and torsion (twisting) are all forces that act individually or in combination to provide mechanical loading that may result in excessive tissue deformation -unloaded (nothing), tension (up and down), compression, shear (rubbing on each other), bending, torsion (around), combined (up and down and around)

Force magnitude

The amount of torque can be determined by multiplying the force magnitude (amount of force usually expressed in newtons) by the force arm

Force arm

The perpendicular distance between the location of force application and the 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.

Displacement

a change in the position or location of an object from its original point of reference

mechanical advantage

advantage gained through the use of machines to increase or multiply the applied force in performing a task; enables a relatively small force to be applied to move a much greater resistance; determined by dividing the load by the effort.

linear motion

also can be called translatory motion, is motion along a line

Wheels and axles

are used primarily to enhance range of motion and speed of movement in the musculoskeletal system, function like a 1st class lever, when a wheel or axle turns, the other must as well

Lever

as a rigid bar that turns about an axis of rotation, or fulcrum. The axis is the point of rotation about which the lever moves. The lever rotates about the axis as a result of force (sometimes referred to as effort, E ) being applied to it to cause its movement against a resistance (sometimes referred to as load or weight)

coefficient of friction

depends on the hardness of the surfaces which helps to determine the amount of friction

Law of reaction

for every action there is an opposite and equal reaction (ground reaction force= force of the surface reacting to the force we place on it)

speed

how fast obj is moving

First class levers

is designed basically to produce Page 75balanced movements when the axis is midway between the force and the resistance (e.g., a seesaw). FAR

second class levers

is designed to produce force movements, since a large resistance can be moved by a relatively small force. Examples: bottle opener, a wheelbarrow, and a nutcracker, triceps extending the elbow in a push-up

angular displacement

is the change in location of a rotating body

linear displacement

is the distance a system moves in a straight line

Increase MA of pulley

may be movable and can be combined to form compound pulleys to further increase the MA, every additional rope connected to a movable pulley increases the MA by 1 (foot motion, ankle down and up) lateral malleolus is the pulley for peroneus longus tendon

Torque

moment of force; is the turning effect of an eccentric force

curvilinear motion (linear)

motion along a curved line

rectilinear motion (linear)

motion is along a straight line

angular motion

moving involving a rotation around an axis (axis=joints)

turning the axle

provides a speed and range of motion advantage of being able to move the outside of the wheel a greater distance at the speed the axle turns

Turning a wheel

provides the force motion advantage of being able to apply a small force to move a larger resistance

Friction

s the force that results from the resistance between the surfaces of two objects moving on each other

Static

systems that are in a constant state of motion, whether at rest with no motion or moving at a constant velocity without acceleration. Involves all forces acting on the body being in balance, resulting in the body being in equilibrium.

Balance

the ability to control equilibrium, either static or dynamic.

Third class levers

the force being applied between the axis and the resistance, are designed to produce speed and range of motion, most levers are this type. requires high force to move even small resistance. ex: catapult, shovel handle, RFA

distance

the path of movement, is the actual sum length it is measured to have travelled

center of rotation

the point or line around which all other points int he body move (a door hinge)

velocity

the rate at which an object changes position, includes the direction and describes the rate of displacement

Mechanics

the study of physical actions of forces, can be subdivided into statics and dynamics