Because the bird will move a short distance through the air while the shot is reaching it. When a body in motion strikes one at rest, is the force felt alike by both bodies? The force is felt alike by both bodies; thus, when one head is struck against another, both are equally hurt. Do bodies, when moving rapidly, strike with more force than when moving slowly? Yes; the force with which they strike depends upon their velocity. What examples of this force may be given? A nail may be driven into a board by a hammer, when it falls rapidly upon the nail; a bullet may be shot through a plank; and even a tallow candle, when shot from a gun, may move with velocity enough to pass through a pine board. Why do large bodies start slowly? Because it takes some time for the force to reach all parts of them. Why is it difficult for horses to start a loaded wagon? Because they must pull some time before the force reaches all parts of the wagon, causing it to move. Why is machinery slow at starting? Because it requires time for the force applied to reach all parts of the machinery. When two solid bodies, moving slowly, strike against each other, what takes place? They are pushed off from each other in opposite directions. Which body is pushed off the more rapidly? The one having the less weight, is pushed off the more rapidly. When the oars of a boat push against the water, what takes place? The boat and the water move in opposite directions. When the wings of a bird strike the air, what takes place? The bird and the air move in opposite directions. How can a duck or a goose swim in the water? The toes of a duck or a goose are joined together by a web which makes the foot broad, like a paddle; and when these broad feet are pressed against the water, the duck or the goose moves forward. Can all birds swim in the water? No; only those birds can swim whose toes are joined together by a web, thus giving them a broad foot to be pushed against the water. What is produced by the rubbing of bodies together? _Friction_ is produced by rubbing bodies together. What does friction tend to do? Friction tends to check the motion of bodies. How do we lessen the friction in machinery? We lessen the friction in machinery by oiling the parts where they rub together. How are waves produced in the water? Waves are produced by the friction of the air upon the water. What causes the water to flow in creeks and rivers? The attraction of gravitation, which causes water always to fall to its lowest level. What retards the current of water in streams? The friction, caused by the water rubbing against the banks and bottoms of the streams, retards their current. In what part of a stream is the current the strongest? It is strongest in the middle of a stream, because there is less friction there. What retards the flow of water through a pipe? The friction of the water against the sides of the pipe, retards its flow very much.