1. The natural state of a body was to be at rest and that it moved only if driven by a force or impulse . 亚里士多德的观点， 自然状态下的物体是静止的，只有在外力或推动力的驱使下才会运动。
At rest : adj. in a state of repose or especially sleep 静止的 Synonyms : asleep
2. The situation is similar to that of heavy bodies falling vertically .
vertically :adv. in a vertical direction 以垂直的方向 Antonyms: horizontally
3. Galileo's measurements were used by Newton as the basis of his laws of motion .
as the basis of ....以..为基础
laws of motion : 运动定律（指下文要提及的牛顿第一和第二定律）
4.This idea was first stated explicitly in Newton's "Principia Mathematica", published in 1687.
explicitly :adv. in an explicit manner . When you explain something explicitly, you do it in great detail, leaving no room for misunderstanding. Synonyms : implicitly ,without ever expressing so clearly
5. ....at a rate that is proportional to the force
proportional : adj. properly related in size or degree or other measurable characteristics; usually followed by `to' , which describes something that has a relative size or amount to something else. Synonyms ： relative . E.g. That being, a statement of probability that is proportional to the amount of available evidence and subject to an informal system of peer review.
6. In addition to his laws of motion, Newton discovered a law to describe the force of gravity.
In addtion to : compare to "besides "; E.g. In addition to health and longevity, she said education is a factor.
gravity: In physics,gravity is the natural force that causes things to fall toward the earth. The noun gravity can also mean seriousness or solemnity(庄严).
7. The orbits of the planets would not be elliptical, they would either spiral in to the sun or escape from the sun.
elliptical : adj. rounded like an egg E.g. Many comets have an elliptical orbit around the Sun that brings them closer at some times and farther away at others.
spiral:n. a structure consisting of something wound in a continuous series of loops 螺旋形. 在这里做V，使成螺旋形
8. He was severely criticized for this irrational belief by many people.
criticized : v. find fault with; express criticism of; point out real or perceived flaws 被批判
Irrational : adj. not consistent with or using reason 不合理的 Usually you use irrational to describe ideas and thoughts that are not based on reason, although emotions and behavior can be irrational too if they don't seem reasonable.
9....they believed that one could unambiguously measure the interval of time between two events......
unambiguous : adj. having or exhibiting a single clearly defined meaning 明确的，不含糊的。此为副词。
interval of time : 时间间距 interval means the distance between things
10. A proper theory of the propagation of light didn't come until 1865.
propagation: n. the movement of a wave through a medium 传播。 同时它还有繁殖的意思
11.Maxwell's equations predicted that there could be wavelike disturbances in the combined electromagetic field.
equations:a mathematical statement that two expressions are equal方程式 In an equation, the quantities on both sides of the equal sign are equal. That's the mathematical meaning ofequation
disturbances： n. activity that is a malfunction, intrusion, or interruption 干扰Synonyms : perturbation. E.g.there was adisturbanceof neural function
electromagetic: adj. pertaining to or exhibiting magnetism produced by electric charge in motion. E.g. electromagnetic energy 电磁能
12. ..and that these would travel as a fixed speed, like ripples on a pond. 池塘里的涟漪
13....a hitherto unknown clerk in the Swiss patent office, Albert Einstein....
hitherto: adv. used in negative statement to describe a situation that has existed up to this point or up to the present time 前无古人，横空出世，好一个爱因斯坦 Use the adverb hitherto when you're describing a state or circumstance that existed up until now. E.g. A rush of electric-car launches over the next three years is likely to hasten their hitherto slow adoption by consumers.
14: the fundamental postulate of the theory of relativity.相对论
postulate: .n. (logic) a proposition that is accepted as true in order to provide a basis for logical reasoning. 基本条件
E.g.Kant’s key postulate was “the creation of an international community based on commerce and free trade.”
15. only light, or other waves that have no intrinsic mass, can move at the speed of light.
intrinsic : adj. belonging to a thing by its very nature 本质的，固有的。e.g. Clearly, the stock was way ahead of itself and likely to eventually fall closer to its intrinsic value.
Synonyms : intrinsical Antonyms: extrinsic.
16. cesium clock : an atomic clock based on the energy difference between two states of the caesium nucleus in a magnetic field 原子钟
17.the choice of coordinates is arbitrary 坐标
arbitrary:adj. based on or subject to individual discretion or preference or sometimes impulse or caprice ; Something that's arbitrary seems like it's chosen at random instead of following a consistent rule. 任意的，随机的。E.g.Critics say that ending voter registration 20 days before Election Day is arbitrary.
18.this cone is called the future light cone of the event. In the same way we can draw another cone, called the past light cone.
cone : n.a shape whose base is a circle and whose sides taper up to a point 圆锥体
By wikipedia, which wrote like this : a light cone is the path that a flash of light, emanating from a single event(localized to a single point in space and a single moment in time) and traveling in all directions, would take through spacetime. To get what's future light cone and past light cone via below picture :
19. the light cones will be identical and will all point in the same direction.
identical: adj. being the exact same one; not any other . Synonyms : very, same . E.g. All of them shared identical mitochondrial genomes, which are inherited from the mother.
20. and has a rather elongated orbit .
elongated: adj. drawn out or made longer spatially . Something that's elongated is stretched out, or extended so that it's longer than usual. Synonyms: extended, prolonged. E.g. “People are asked a question, and they preface their answer with an elongated ‘ soooo.