电动车起步很猛，为什么跑高速反而特别耗电？
Why do electric cars accelerate briskly yet drain fast on the highway?
电机在低速就能输出最大扭矩，所以起步猛。但空气阻力随速度平方增长、功率随速度立方增长，120公里每小时时克服风阻的功率可能是60公里每小时的八倍，续航因此明显缩短。
Electric motors give full torque from a standstill, hence the brisk launch. But aerodynamic drag grows with the square of speed and the required power with its cube, so at 120 km/h the car may need eight times the power it needed at 60 km/h.
难度 专业 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-10-03 · 3 条独立证据
来源 · Source
Halliday、Resnick 与 Walker，《物理学基础》（第10版）
Halliday, Resnick & Walker, 'Fundamentals of Physics' (10th ed.)
独立核验依据 · Independent verification: 核验依据 2 angusrobertson.com.au
#空气阻力 #功率 #电动车
两列高铁交会时，车厢里为什么有被“推一下”的感觉？
Why do you feel a shove when two high-speed trains pass each other?
两车之间的狭窄空气被迅速挤出，流速升高、压强降低，把车身互相吸近；随后压力波掠过又把车推开。这一吸一推在密闭车厢里就成了明显的晃动感。
Air squeezed through the narrow gap speeds up and drops in pressure, pulling the cars toward each other, and then a pressure wave pushes them apart. Inside the sealed cabin that suction-then-push feels like a shove.
难度 进阶 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-10-03 · 3 条独立证据
来源 · Source
Halliday、Resnick 与 Walker，《物理学基础》（第10版）
Halliday, Resnick & Walker, 'Fundamentals of Physics' (10th ed.)
独立核验依据 · Independent verification: 核验依据 2 angusrobertson.com.au
#伯努利 #压力波 #高铁
飞机降落前为什么要把襟翼放出来？
Why do pilots extend the flaps before landing?
放襟翼增大了机翼的弯度和有效面积，同样速度下能产生更大升力，于是失速速度下降。这让飞机可以用更慢、更安全的速度接地，同时增加阻力帮助减速下沉。
Extending flaps increases the wing's camber and effective area, giving more lift at the same speed and lowering the stall speed. The plane can therefore touch down more slowly, while the added drag helps it descend and slow.
难度 进阶 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-11-03
来源 · Source
Anderson，《空气动力学基础》（第5版）
Anderson, 'Fundamentals of Aerodynamics' (5th ed.)
独立核验依据 · Independent verification: 核验依据 1 OPENLIBRARY 标识 /works/OL20903326W：Fundamentals of aerody
#升力 #襟翼 #航空
为什么货船造得越大，每吨货的油耗反而越低？
Why does a bigger cargo ship burn less fuel per tonne of cargo?
这源于“缩放律”。船的载货量（近似与体积）随尺度立方增长，而航行阻力主要来自船体浸水表面积（尺度平方）的摩擦和兴波，增长更慢。于是单位载货量所分摊的阻力随船变大而减小，推进所需功率的增长慢于载货量增长，所以每吨货物摊到的油耗下降——即“规模经济”的流体力学版本。当然实际还受港口、航道等限制。
This is a scaling-law effect. A ship's cargo capacity scales roughly with its volume (cube of size), while hydrodynamic drag comes mainly from wetted surface area (square of size) and wave-making, growing more slowly. So the drag per unit of cargo shrinks as the ship gets bigger, and the power needed to propel it grows slower than its carrying capacity—meaning fuel per tonne of cargo falls. It is the fluid-dynamic version of economies of scale, bounded in practice by ports and channels.
难度 进阶 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-10-03 · 3 条独立证据
来源 · Source
Halliday、Resnick 与 Walker，《物理学基础》（第10版）
Halliday, Resnick & Walker, 'Fundamentals of Physics' (10th ed.)
独立核验依据 · Independent verification: 核验依据 2 angusrobertson.com.au
#缩放律 #阻力 #航运
地铁刹车时的“再生制动”，能量到哪里去了？
Where does the energy go during a subway's regenerative braking?
地铁刹车时的“再生制动”把列车动能通过牵引电机反转成发电机模式，转化为电能。这部分电能先供给同一电网中正在加速或运行的邻近列车使用；若本段电网无需求，则通过电阻栅以热的形式耗散，或回馈给电网/储能装置（如超级电容、飞轮）。因此再生制动回收了相当比例的刹车能量，降低了整体能耗。
During regenerative braking, a subway train's traction motors run backward as generators, converting kinetic energy into electricity. That power is first fed to other trains on the same network that are accelerating or running; if there is no local demand, it is dissipated as heat in resistor grids or fed back to the grid or stored in devices like supercapacitors or flywheels. Regenerative braking thus reclaims a significant share of braking energy and lowers overall consumption.
难度 进阶 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-10-03 · 3 条独立证据
来源 · Source
Halliday、Resnick 与 Walker，《物理学基础》（第10版）
Halliday, Resnick & Walker, 'Fundamentals of Physics' (10th ed.)
独立核验依据 · Independent verification: 核验依据 2 angusrobertson.com.au
#再生制动 #能量回收 #地铁
轮胎气压偏低为什么会更费油？
Why does under-inflation waste fuel?
气压低时轮胎变形更大，橡胶反复挤压又回弹，内部的黏性损耗把能量变成热。这个滚动阻力增加，发动机就要多做功。
A soft tyre deforms more, and the rubber flexing back and forth turns energy into heat through internal friction. That extra rolling resistance forces the engine to do more work.
难度 入门 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-10-03 · 3 条独立证据
来源 · Source
Halliday、Resnick 与 Walker，《物理学基础》（第10版）
Halliday, Resnick & Walker, 'Fundamentals of Physics' (10th ed.)
独立核验依据 · Independent verification: 核验依据 2 angusrobertson.com.au
#滚动阻力 #迟滞损耗 #省油
长下坡一直踩刹车，为什么刹车会“失灵”？
Why can brakes fade after a long downhill?
刹车把重力势能变成摩擦热，长时间下坡热量来不及散掉，刹车片温度可以升到几百摄氏度。摩擦系数随高温下降，制动液还可能汽化产生气泡，踏板就变软发飘。
Brakes convert gravitational energy into heat faster than it can escape, and the pads can reach several hundred degrees. The friction coefficient falls with temperature and the fluid can even boil into bubbles, leaving the pedal soft.
难度 入门 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-10-03 · 3 条独立证据
来源 · Source
Halliday、Resnick 与 Walker，《物理学基础》（第10版）
Halliday, Resnick & Walker, 'Fundamentals of Physics' (10th ed.)
独立核验依据 · Independent verification: 核验依据 2 angusrobertson.com.au
#摩擦热 #热衰退 #行车安全
坐飞机起飞和降落时，为什么耳朵会疼？
Why do our ears hurt when a plane takes off and lands?
高空的空气比地面稀薄，机舱里的气压会变。耳朵里面还是原来的气压，鼓膜两边不一样就被顶得难受；咽口水或打哈欠能让小管道打开，把气压放平。
Cabin pressure changes as the plane climbs or descends, but the air trapped behind your eardrum does not, so the drum gets pushed. Swallowing or yawning opens a little tube and evens the pressure out.
难度 入门 · 适合 幼儿(3-6)
CC BY 4.0 · 已核验 · Verified 2026-10-03 · 3 条独立证据
来源 · Source
Halliday、Resnick 与 Walker，《物理学基础》（第10版）
Halliday, Resnick & Walker, 'Fundamentals of Physics' (10th ed.)
独立核验依据 · Independent verification: 核验依据 2 angusrobertson.com.au
#气压 #鼓膜 #飞行