SOME NOTIONS ABOUT MOTION

Date: 2015-10-07; view: 469.

Which falls faster: a blade of grass or a stone? Anyone can see that a stone falls faster. And that is what the ancient Greeks believed. Based on everyday experience Aristotle determined that heavy objects fall faster than light objects and that objects fall with a speed proportional to their weight.

Aristotle also studied horizontal motion. He observed that whenever he pushed a rock or other object, it always rolled for a while and then came to rest. He hypothesized that the natural state of an object is to be at rest and a force is necessary to keep an object in motion. Aristotle's hypotheses were accepted for 2000 years because they were consistent with logic and informal observation.

It was not until the early 1600s that these long-established believes were challenged. Galileo was not content to accept ideas without verifying them with experiments. He dropped various weights from a height and recorded the results. Disproving Aristotle's hypothesis, he determined that all bodies fall at equal rates, if you discount the air resistance. A blade of grass will fall more slowly than a stone only because it meets with more resistance from the air,

Galileo also disproved Aristotle's hypothesis about horizontal motion. He demonstrated that a body pushed at a smooth surface could go much further than a body pushed at a rough surface. When a lubricant, such as oil, was used, almost no force was required to keep the object in motion. He concluded that if an object doesn't meet with resistance (friction), it will continue to move if no force is applied.

Half a century later, I. Newton extended Galileo's ideas and formulated a theory that a body at rest will remain at rest and a body in motion will remain in motion unless some outside force acts on it. This theory is so universally accepted that it's referred to as Newton's first law of motion.

Ex.11. Translate the following word combinations into Russian:

a blade of grass; heavy objects; light objects; horizontal motion; to push a rock; to come to rest; to be at rest; to keep an object in motion; to accept hypotheses; to be were consistent with logic and informal observation; to challenge long-established believes; to verify something; various weights; to record the results; to disprove hypothesis; at equal rates; to meet resistance; a smooth surface; a rough surface; to require force; to apply force; to formulate a theory; to remain in motion; to remain at rest; to refer to a theory.