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In general, motion is classified according to the anatomical plane it occurs in. Flexion and extension are examples of angular motions, in which two axes of a joint are brought closer together or moved further apart. Rotational motion may occur at other joints, for example the shoulder, and are described as internal or external.
Some sources also state that the triceps surae and extensor hallucis longus invert. [6]: 123 Inversion occurs at the subtalar joint and transverse tarsal joint. [7] Eversion of the foot occurs at the subtalar joint. The muscles involved in this include fibularis longus and fibularis brevis, which are innervated by the superficial fibular nerve.
Every object perseveres in its state of rest, or of uniform motion in a right line, except insofar as it is compelled to change that state by forces impressed thereon. [note 3] Newton's first law expresses the principle of inertia: the natural behavior of a body is to move in a straight line at constant speed. A body's motion preserves the ...
Examples of this form of articulation are found in the hip, where the round head of the femur (ball) rests in the cup-like acetabulum (socket) of the pelvis; and in the shoulder joint, where the rounded upper extremity of the humerus (ball) rests in the cup-like glenoid fossa (socket) of the shoulder blade. [2]
Blows can also affect equilibrioreception, especially those to the side of the head or directly to the ear. Most astronauts find that their sense of balance is impaired when in orbit because they are in a constant state of weightlessness. This causes a form of motion sickness called space adaptation syndrome.
A collision between two pool balls is a good example of an almost totally elastic collision, due to their high rigidity, but when bodies come in contact there is always some dissipation. [9] A head-on elastic collision between two bodies can be represented by velocities in one dimension, along a line passing through the bodies.
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In accordance with Newton's third law of motion, the body in curved motion exerts an equal and opposite force on the other body. This reactive force is exerted by the body in curved motion on the other body that provides the centripetal force and its direction is from that other body toward the body in curved motion. [40] [41] [42] [43]