3 Describe about the freely moveable joint?
Answers
A corrie is an armchair-shaped hollow found on the side of a mountain. This is where a glacier forms. In France corries are called cirques and in Wales they are called cwms.
How does a corrie form?
Snow collects in a sheltered hollow on the side of a mountain. This is usually on North-facing slopes in the northern hemisphere. The snow doesn't melt in the summer because it is high up, sheltered and cold.
Every winter, more snow collects in the hollow. This becomes compacted and the air is squeezed out leaving ice.
The back wall of the corrie gets steeper due to freeze-thaw weathering and plucking.
The base of the corrie becomes deeper due to abrasion.
As the glacier gets heavier it moves downhill. The glacier moves out of the hollow in a circular motion called rotational slip.
Due to less erosion at the front of the glacier a corrie lip is formed.
After the glacier has melted a lake forms in the hollow. This is called a corrie lake or tarn.
Rocks are plucked from glacier, and move downwards through rotational slip. Rocks rub against the glacier causing abrasion. Moraine builds as ice melts at the corrie lip.
Corrie features
Corries produce the following erosional features:
arêtes - this is a narrow ridge of land that is created when two corries erode back towards each other
pyramidal peak - if three or more corries erode back towards each other, at the top of a mountain a pointed peak is left behind
Other features of erosion
When a glacier moves downhill it erodes everything in its path through abrasion and plucking. Glaciers usually follow the easiest route down a mountain, which is often an old river valley. Interlocking spurs created by a river are eroded at the ends by the glacier to create truncated spurs. After the glacier has melted it leaves a U-shaped glacial trough. Sometimes the glacial trough fills with water, called a ribbon lake. Old tributaries, which would have once fed into the valley are left suspended and are known as hanging valleys.
A U-shaped valley has a flat floor and steep sides. Interlocking spurs eroded by the river are called truncated spurs. Hanging valleys are left by old tributaries. A ribbon lake may form in the river.
The joints between our bones are part of what help us to move and keep the bones connected. They have different kinds of classifications depending on the type of movement. Some joints have more range of movement than others.
On the basis of movement the following types of movable joints are as:
(i) Ball and socket joint: In this type of joint the ball-shaped head of a bone is fitted in such a manner in the socket made by another bone, Which allows free movement in all directions. For example, the joint between the head of the humerus and glenoid cavity of the pectoral girdle.
(ii) Pivot joint: In Pivot joint, a pointed end of a bone is fitted in a pit of another bone is such manner that the later can show rotational movement around the former. For example, the joint between axis vertebra and atlas vertebra holding the skull.
(iii) Hinge joint: At such joints, one bone can move in one direction up to a certain limit, like the hinge of doors and windows. For example, Knee, elbow etc.
(iv) Saddle joint: This joint is like ball and socket joint but; less developed. 'There is no free movement of the ball inside the socket, only a limited movement is allowed. For example, metacarpal of thumb and trapezium of the wrist.
(v) Gliding joints: In gliding joints the surfaces of bones at the joint are flat, so the bones glide over each other. Example, tibia, and fibula, between articular processes of vertebrae, between clavicle and sternum.