WEBVTT 1 00:00:01.906 --> 00:00:04.727 Movement is a characteristic of the living world. 2 00:00:04.728 --> 00:00:11.780 It corresponds to a displacement in space, of the whole body or of one of its parts. 3 00:00:11.781 --> 00:00:16.639 Movement is made possible by the contraction and extension of muscles. 4 00:00:16.640 --> 00:00:20.687 These are under the direction of the central nervous system. 5 00:00:20.688 --> 00:00:25.026 Among the vertebrates, skeletal muscles are connected to bones by tendons 6 00:00:25.027 --> 00:00:28.942 which enables the use of the joints. 7 00:00:28.943 --> 00:00:34.372 This work requires a continual input of energy, principally in the form of glucose. 8 00:00:36.284 --> 00:00:41.821 Legs, wings and fins are referred to as limbs. 9 00:00:41.822 --> 00:00:47.045 These are perfectly adapted to the milieu in which the animal evolves. 10 00:00:47.046 --> 00:00:50.232 In pushing on the ground, the air or on water 11 00:00:50.233 --> 00:00:55.483 a limb produces pressure that is at the origin of the propulsive force. 12 00:00:55.484 --> 00:00:59.009 Thus, the horse’s hoof pushes the ground toward the rear, 13 00:00:59.010 --> 00:01:02.692 which propels the body forward. 14 00:01:02.693 --> 00:01:05.827 In the same way, the wings of a bird drive air downward 15 00:01:05.828 --> 00:01:10.033 which produces an upward force that keeps the bird in the air. 16 00:01:10.870 --> 00:01:13.350 We should understand that the displacement is possible 17 00:01:13.351 --> 00:01:16.877 because the medium offers resistance. 18 00:01:16.878 --> 00:01:21.814 Movements are often rapid and involve numerous muscles. 19 00:01:21.815 --> 00:01:26.777 It is very interesting to decompose a movement into simple images. 20 00:01:26.778 --> 00:01:31.505 This is what Etienne Jules Marey in France, and Edward Muybridge in the United States 21 00:01:31.506 --> 00:01:36.155 did near the end of the 19th century, thanks to chronophotography. 22 00:01:36.156 --> 00:01:38.976 This technique, an ancestor of the motion picture 23 00:01:38.977 --> 00:01:41.977 enables one to obtain several images per second.