【单词】equals 原型：equal ['ee-kwuhl]['i?kw?l] vt. 比得上；等于
【单词】curvature ['kur-vuh-cher]['k??v?t??] n. 弯曲；（几何）曲率
【单词】foot [foo?t][f?t] n. 英尺
【单词】downward ['doun-werd]['da?nw?d] adv. 向下
【单词】traveled 原型 travel ['trav-uhl]['tr?vl] v. 移动 ， 旅行
You never get any closer to the earth, and so you just keep going around and around.
【译】你不会离地球更近，所以你就一直绕来绕去 。
The hard part of getting into orbit isn't the altitude, it's reaching the horizontal speed necessary to orbit.
【译】进入轨道最困难的部分不是高度，而是达到进入轨道所需的水平速度 。
【短语】part of … （某事物的）一部分；例句：He received part of his education in England. 他有一部分教育是在英国接受的 。
【单词】reaching 原型：reach [reech][ri?t?] v. 到达；伸出；达成
【单词】horizontal [hawr-uh-'zon-tl, hor-][?h?r?'z?ntl] adj. 水平的；横的
【单词】speed [speed][spi?d] n. 速度；迅速
It's VERY fast, and so it takes a lot of thrust to get there.
【译】这需要很快 ， 所以需要很大的推力才能达到这个速度 。
"Up" is easy.
【译】“向上”很容易 。
That's not what lets you enter orbit, though.
【译】但这并不是让你进入轨道的原因 。
You have to go sideways.
【译】你得向侧面移动 。
【单词】sideways ['sahyd-weyz]['sa?dwe?z] adv. 向旁边；斜着地；向侧面地
An object in orbit is locked by gravity to the thing its orbiting, it's just going fast enough sideways such that its continued "falling" continually misses the orbited object.
【译】一个在轨道上的物体被重力锁定在它的轨道上，它的侧向运动速度足够快，以至于它持续“下坠”然而并不会向它围绕的物体靠近 。
【单词】object ['ob-jikt, -jekt]['?bd??kt] n. 物体；目标；对象
【单词】locked 原型：lock [lok][l?k] v. 固定；锁(住)；抓牢
【单词】orbiting 原型：orbit ['awr-bit]['??b?t] vt. 绕轨道而行；进入轨道 vi. 盘旋
【单词】continually [kuhn-'tin-yoo-uh-lee][k?n't?nju?li] adv. 不断地；频繁地
Things orbit the earth because of gravity.
【译】由于引力，物体绕地球运行 。
【fighting怎么读英语 fighting怎么读】If you "broke free of gravity" you would just leave the earth, going further and further from it.
【译】如果你“挣脱了重力”，你就会离开地球，离地球越来越远 。
You are right though, as you go up, there is less drag and less gravity.
【译】但你是对的 ， 当你往上爬时，阻力和重力都变小了 。
But to get into orbit, very little of the energy is spent going up and fighting drag.
【译】但要进入轨道 ， 仅需要很少的能量花在上升和抵抗阻力上 。
【单词】spent 原型：spend [spend][spend] v. 花费；浪费
【单词】fighting 原型：fight [fahyt][fa?t] vt. 对抗
Most of the energy is spent accelerating sideways.
【译】大部分能量都花在侧向加速上 。
【短语】most of … 大部分，大多数的；绝大多数；例句：I think most of these obstacles can be surmounted. 我认为这些障碍大多数都是可以克服的 。
【单词】accelerating 原型：accelerate [ak-'sel-uh-reyt][?k'sel?re?t] v. 加速；提前
With an orbit, gravity is still pulling you down, but because you go so fast sideways, you "miss the Earth," so you just swing around it.
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