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?