轮船的压载水舱起什么作用？
What is the purpose of a ship's ballast tank?
空船太轻会重心高、易翻且螺旋桨吃水不够，向底部压载舱注海水可压低重心、保持吃水深度和平稳，装货后排出水来调节。
An empty ship is too light with a high center of gravity and poor propeller depth; flooding ballast tanks with seawater lowers the center of gravity, keeps draft and stability, then water is pumped out as cargo loads.
难度 专业 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-10-04
来源 · Source
Tupper，《船舶原理导论》（第5版）
Tupper, 'Introduction to Naval Architecture' (5th ed.)
独立核验依据 · Independent verification: 核验依据 1 ISBN 9780080982373 (2013)
#交通 #压载舱 #稳性
磁悬浮列车是怎样悬浮又前进的？
How does a maglev train levitate and move forward?
列车和轨道上的超导或电磁铁同性相斥（或吸吊）使车悬浮离轨，再用沿线变化的磁场推着车厢前进，没有轮轨摩擦所以又快又安静。
Repelling or attracting magnets lift the train off the track, and a traveling magnetic field along the guideway pushes the car forward; with no wheel friction it is fast and quiet.
难度 专业 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-11-03
来源 · Source
Moon，《超导悬浮》（1994）
Moon, F.C., 'Superconducting Levitation' (1994)
独立核验依据 · Independent verification: 核验依据 1 OPENLIBRARY 标识 /works/OL2676003W：Superconducting levitat
#交通 #磁悬浮 #磁力
液化天然气船为什么被称为海上冰壶?零下162度的甲烷怎么安全运输?
Why call LNG carriers floating thermoses — how is methane kept safe at minus 162 degrees Celsius?
天然气冷却到零下162度变成体积缩水六百倍的液体,才值得跨洋运输。LNG船的绝热是生命线:主流薄膜型围护中,NO96系统用平面因瓦合金膜加珍珠岩绝缘箱,Mark III系统用波纹不锈钢膜加聚氨酯泡沫,日蒸发率控制在0.1%量级;蒸发的气体或当燃料烧掉,或再液化回舱。最怕低温液货接触船体钢致其瞬间脆裂,故接触层用耐低温合金并设二次屏障。加上惰性气体置换防爆,LNG船队至今保持着良好的安全记录。
Chilled to minus 162 degrees Celsius, natural gas shrinks six-hundredfold into liquid worth shipping across oceans. Insulation is the lifeline: among mainstream membrane systems, NO96 pairs flat Invar membranes with perlite-filled boxes while Mark III uses corrugated stainless-steel membranes with polyurethane foam, holding boil-off near 0.1 percent daily; evaporated gas burns as fuel or reliquefies into the tank. Cryogenic cargo touching hull steel would embrittle it instantly, so contact layers use cryogenic alloys behind full secondary barriers; with inert-gas purging, LNG fleets have maintained a strong safety record.
难度 专业 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-10-04
来源 · Source
Mokhatab 等,《Handbook of Liquefied Natural Gas》,Gulf Professional Publishing,2014
S. Mokhatab, J. Y. Mak, J. V. Valappil and D. A. Wood, Handbook of Liquefied Natural Gas, Gulf Professional Publishing, 2014
独立核验依据 · Independent verification: 核验依据 1 ISBN 9780124046450 (2013)
#LNG船 #低温脆性 #薄膜型围护
飞机翅膀上的襟翼（ flaps ）有什么用？
What are the flaps on airplane wings for?
起飞和降落时放下襟翼，让机翼面积变大、弯度增加，从而在低速度下也能产生足够升力并增加阻力减速，使短跑道起降更安全。
Extended during takeoff and landing, flaps enlarge and curve the wing to make enough lift at low speed and add drag to slow down, enabling short-runway, safer operations.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-11-02
来源 · Source
Anderson，《空气动力学基础》（第6版）
Anderson, 'Fundamentals of Aerodynamics' (6th ed.)
独立核验依据 · Independent verification: 核验依据 1 ISBN 9787516504413（豆瓣书目条目: 空气动力学基础）
#交通 #飞机 #襟翼
潜水艇是怎样下潜和上浮的？
How does a submarine dive and surface?
潜艇有可注水和排水的压载舱：注水变重就下沉，用压缩空气把水排出变轻就上浮，靠调节重量来控制停在任意深度。
Ballast tanks fill with water to get heavier and sink, or are blown empty with compressed air to get lighter and rise; adjusting weight holds any depth.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-10-04
来源 · Source
Tupper，《船舶原理导论》（第5版）
Tupper, 'Introduction to Naval Architecture' (5th ed.)
独立核验依据 · Independent verification: 核验依据 1 ISBN 9780080982373 (2013)
#交通 #潜艇 #压载
红绿灯是怎样相互配合、让车流更顺畅的？
How do traffic lights coordinate to keep traffic flowing?
路口控制器按预设周期或实时车流量调整各方向红绿灯时长，并和相邻路口联动错开放行，减少停车等待，主干道常做成绿波带。
Controllers set green times by schedule or live traffic and link neighboring intersections to release waves of cars in turn, cutting stops; main roads often run a green wave.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-11-02
来源 · Source
ITE，《交通工程手册》（第7版）
ITE, 'Traffic Engineering Handbook' (7th ed.)
独立核验依据 · Independent verification: 核验依据 1 ISBN 9787114026225（豆瓣书目条目: 交通工程手册）
#交通 #信号 #协调
环岛（转盘）为什么比普通十字路口更安全？
Why is a roundabout safer than a normal cross intersection?
车进环岛要绕圈慢行、互相礼让，把容易撞车的直角交叉变成温柔的绕行，车速更低、冲突点更少，事故也就更少。
Drivers slow and yield while circling, turning harsh right-angle crossings into gentle merges with fewer conflict points and lower speeds, so crashes drop.
难度 入门 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-11-02
来源 · Source
ITE，《交通工程手册》（第7版）
ITE, 'Traffic Engineering Handbook' (7th ed.)
独立核验依据 · Independent verification: 核验依据 1 ISBN 9787114026225（豆瓣书目条目: 交通工程手册）
#交通 #环岛 #安全
大船那么重，为什么还能浮在水面上？
Ships are so heavy, so why do they float?
船体是中空的，排开的水重量等于船的重量时就浮着；只要船的平均密度比水小，再重也能浮，就像一块空心铁盒子能漂。
A ship is hollow, so it displaces water weighing as much as itself and floats; if its average density is less than water, even a heavy hull stays up, like a hollow iron box.
难度 入门 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-10-04
来源 · Source
Tupper，《船舶原理导论》（第5版）
Tupper, 'Introduction to Naval Architecture' (5th ed.)
独立核验依据 · Independent verification: 核验依据 1 ISBN 9780080982373 (2013)
#交通 #浮力 #轮船
缆车是怎样把人拉上很陡的山坡的？
How does a cable car pull people up a very steep hill?
山顶和山脚有轮子绕着一根钢缆转，缆绳紧紧抓住钢缆被带着走，电机在上方拉绳，所以再陡的坡也能稳稳上下。
Wheels at top and bottom loop a steel cable, the car grips the cable and is carried along while a motor up top pulls the rope, so even steep slopes are climbed safely.
难度 入门 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-11-03
来源 · Source
Vuchic，《城市轨道与公交系统》（第2版）
Vuchic, V.R., 'Urban Public Transportation Systems' (2nd ed.)
独立核验依据 · Independent verification: 核验依据 1 OPENLIBRARY 标识 /works/OL22643579W：Urban public transport
#交通 #缆车 #钢缆
自行车的轮子为什么是圆的,不是方方的?
Why are bike wheels round instead of square?
圆轮子滚起来又稳又顺,骑车的人不会被颠得一跳一跳。方轮子的角会磕磕绊绊,骑一下卡一下。轮子转一圈,车就稳稳地向前走一大步!
Round wheels roll smooth and steady; square corners would bump and jolt every step. One turn of a round wheel carries you smoothly far ahead!
难度 入门 · 适合 幼儿(3-6)
CC BY 4.0 · 已核验 · Verified 2026-10-03 · 2 条独立证据
来源 · Source
David Macaulay,《The Way Things Work》,Houghton Mifflin,1988
David Macaulay, The Way Things Work, Houghton Mifflin, 1988
独立核验依据 · Independent verification: 核验依据 2 OPENLIBRARY 标识 /works/OL15130328W：The Way Things Work（按标
#轮子 #圆形 #滚动
磁悬浮列车没有轮子,它是怎么浮起来跑的?
How do maglev trains float without wheels?
同名磁极互相排斥——工程师让轨道和列车底部产生强大的排斥力,把几十吨重的列车托离轨道一厘米左右,悬浮滑行。没有轮轨摩擦,它就能安静地跑得又快又稳,时速可达四百多公里,试验中甚至突破每小时600公里,比很多飞机起飞还快。
Like poles repel: engineers make track and train push apart with mighty magnetic force, lifting the train about one centimeter above the guideway to glide. Without wheel friction it runs quietly and smoothly at over four hundred kilometers per hour — test runs have even passed six hundred — faster than many planes take off.
难度 入门 · 适合 小学低段(6-8)
CC BY 4.0 · 已核验 · Verified 2026-10-03 · 2 条独立证据
来源 · Source
《十万个为什么》第六版建筑与交通分册,少年儿童出版社,2013
Ten Thousand Whys: Architecture and Transportation volume, 6th ed., Juvenile and Children Publishing House, 2013
独立核验依据 · Independent verification: 核验依据 1 ISBN 978-7-5324-9328-9 · 核验依据 2 ISBN 9787532493289
#磁悬浮 #磁极排斥 #无摩擦