MECHANICAL ANALYSIS
TERMS & PRINCIPLES
CENTER OF GRAVITY - is that point at which all of the weight of an object may be considered to be concentrated.
EQUILIBRIUM - is the state of a body in which there is not change in its motion.
FORCE- is that which produces or prevents motion, or has a tendency to do so. A push or a pull.
LINEAR MOTION - is motion along a line.
PARALLEL FORCES - are forces acting in the same or opposite direction.
RESULTANT FORCE - is the single force which has the same effect as two or more forces acting in the same direction.
ROTARY MOTION - is motion about a point which acts as a pivot.
TORQUE - is the product of a force and the length of the moment arm on which it acts.
ENERGY - is the ability to do the work.
INERTIA - is the property of matter which requires that a force be exerted on it in order to change its position or motion.
A LAW - is a statement of scientific fact concerning natural phenomena.
MASS - is the measure of the quantity of matter or measure of the inertia of a body.
WEIGHT - is the measure of the attractive force of the earth for a body.
ACCELERATION - is the rate of change of velocity.
ANGULAR VELOCITY - is the rate of rotary motion.
CENTRIFUGAL REACTION - is the reaction force which is equal in magnitude to the centripetal force but acts in the opposite direction.
CENTRIPETAL FORCE - is the force that deflects a body from its linear path and compels it to move along a curve.
CIRCULAR MOTION - is the motion of a body along a curved path of constant radius.
MOMENTUM - is the product of the mass of an object and its velocity.
MOTION - is a continuing change of place of position.
SPEED - is the rate of motion.
VELOCITY - is the rate of displacement.
EFFICIENCY - is the ratio of the actual mechanical advantage to the ideal mechanical advantage; the ratio of the output to the input.
The IDEAL MECHANICAL ADVANTAGE - is the ratio of the distance the effort force moves to the distance the resistance forces moves.
INPUT - is the product of the effort force and the distance through which it acts.
KINETIC ENERGY - is the energy due to the motion of a mass.
POTENTIAL ENERGY - is stored energy, or energy due to the position of a mass.
POWER - is the time rate of doing work.
MECHANICAL PRINCIPLES
1. Every body continues in its state of rest or of uniform motion in a straight line except insofar as it is compelled by forces to change that state.
2. The acceleration of a body is proportional to the force causing it.
3. For every action there is always an equal and contrary reaction.
4. Stability is directly proportional to the area of the base on which the body rests.
5. Stability in a given direction is directly proportional to the horizontal distance of the center of gravity from that edge of the base toward the given direction of movement.
6. Stability is directly proportional to the weight of the body.
7. Stability is indirectly proportional to the distance of the body above the base.
8. For equilibrium to exist, the center of gravity of a body must fall within its base.
9. To start quickly in one direction, keep the center of gravity as high as possible and as near as possible to the edge of the base in the direction of movement.
10. For greatest immobility or stability, increase the area of the base and lower the center of gravity as much as is consistent with the activity involved.
11. To stop quickly when in rapid motion, spread the base and drop the center of gravity as low as possible consistent with subsequent movements.
12. A body is in equilibrium when its center of gravity falls within its base. It loses equilibrium when the center of gravity falls outside of the base.
13. In all arm support activities, the center of gravity of the body should be as nearly as possible over the point of support. (the hands)
14. Movements of the body when suspended in the air or when hanging by arms or legs follow a definite pattern which tends to maintain body balance.
(a) When the body is free in the air, if the head
and feet move up, the hips move down and vice
versa.
(b) When either hands or feet are supported, if
one moves up, then the other moves down and
vice versa.
15. If a performer is in the air free of support, the height to
which the center of gravity can be raised above the floor cannot
be effected by body movements, but the position of the center
of gravity within the body can be changed and the body may be
lowered or raised above the floor by the movement or change in
position of a member of the body.
16. In throwing, jumping, or kicking activities where horizontal distance is the goal, the body or the object should be projected at an angle of approximately, but not greater than 45 degree. This does not hold when air resistance is a controlling factor.
17. In throwing, jumping, or kicking activities where horizontal distance is the goal, the highest speed possible should be attained at the moment of release or take-off.
18. When the angular velocity is constant, the linear velocity
of a point about the center of rotation is directly proportional
to the radius and conversely.
19. In swinging exercises, shortening the radius of rotation on
the upswing will accelerate the movement. Lengthening the radius
on the down swing increases the linear velocity of the center
of gravity at the bottom of the swing.
20. There must be an integration of forward linear motion with rotary motion in order to obtain the best results in many activities.
21. When converting rotary motion to linear motion, the greatest
speed is transferred when the linear direction is at right angles
to the radius connecting the point of release and the
center of rotation.
22. In doing exercises that necessitate pulling the body up and then pushing it further upward, there should be no pause between the pull-up and push but rather the movement should be continuous.
23. The total effective force may be the sum of the forces
of each member of the body if applied in a single direction and
in the proper sequence.
(a) When successively added, each force should be started at the
point of greatest velocity but least acceleration of the preceding
force.
(b) If the forces are applied simultaneously, theywill be limited
by the weakest force of the group of forces.
24. Additional distance from the point of striking a ball may be gained by bending a joint.
25. A body is frequently put in motion by the transfer of momentum from a part of the whole.
26. the direction of body free in the air is determined by the direction of the resultant of the forces which set it in motion.
27. When a limb is used to turn the body of another, the individual turned must resist the force of the thrower by moving the limb against the force.
28. When blows are struck by an implement held in the hand
the grip must be as firm as possible at the moment of impact.
29. If it is desired to absorb the shock of a blow, a fall, a
throw, or a kick, the shock should be spread over either as large
an area as possible or as long a distance as possible or both.
30. Reaction to angular movement in athletics is balanced by rotation in the opposite direction.
31. In throwing or pushing activities, one or both feet are kept in a firm contact with the ground until the object is released in order that the total effect of the effort may be in the direction of the throwing force.
32. The mechanical advantage of a lever is represented by the ratio of the length of the power arm to the length of the weight arm.
33. The longer the power arm of the lever, the greater the moment of force.
34. The shorter the power arm in proportion to the length of the weight arm, the smaller is the moment of force but the more immediate is the action.
35. To be most effective, the force must be directed at right angles to the lever.
36. Mounting movements in swinging exercises should usually start as the center of gravity passes a point directly below the point of support.
37. The longer the radius of rotation the greater the centrifugal force with the same angular velocity and weight.
38. In general, force should be applied as directly as possible in the direction of the intended motion so that as much of the force as possible can be utilized as effective force.
39. The greater the centrifugal force the greater the lean or the banking necessary to balance the force.
40. The direction of flight of a ball which has been struck depends upon the fact that angle of reflection equals the angle of incidence.
41. The coefficient of friction is independent of the area of contact of the two surfaces.
42. The speed of flight of a struck ball depends upon the weight and striking force of the ball and bat and the coefficient of restitution of the ball and of the bat.
43. The laws of aerodynamics control the reaction of air-borne
bodies to the air stream which they divert.
44. The reaction produced by the air stream is proportional to
the active surface area of the body over which the air stream
passes and to the square of the velocity of the air
stream with respect to the body. The angle of inclination determines
the active surface area.
45. The spin of an object produces a stabilizing effect upon it.
46. The reaction of a spinning object after impact with a wall or a stationary surface is dependent upon the direction of spin.
47. In swimming, speed is developed as much by overcoming resistance as by increasing force.
48. In the human body, the available force varies inversely with the velocity of movement.
49. In jumping activities, the depth of the crouch or the angle formed by the femor and the tibia is directly proportional to the strength of the muscles.
50. A muscle contracts with more force when first put under stretch.
51. A muscle will quickly lose its elasticity if it is put under stretch too often and for too long a period of time.
52. Because the body operates under a system of levers that are largely third-class, its movements are adapted more to speed than to strength.
53. Twister movements which are started before the body is airborne will be in the direction of movement of those members of the body which are used to create it.
54. Twister movements which are started after the body is airborne will be in the opposite direction to the movement of the members of the body which are used to create it.
55. Forward rotation is faster when a twister is brought into the movement.
56. Work equals the force times the distance through which the force acts.
57. Kinetic energy equals 1/2 the mass or weight divided by the gravity of the body being moved times the velocity of movement squared.
58. Power equals force times velocity and it has been found that force varies directly with the square of the velocity and power with the cube of the velocity.
59. Techniques performed in accordance with the laws of physics produce the best results with the least expenditure of energy.
60. There may be expenditure of energy without motion, in athletic activities. This energy appears as heat.