未登录,请登录后再发表信息
最新评论 (0)

浮力

Buoyancy

我们知道物体向地球掉落
We know that objects fall towards the Earth
是因为重力作用于他们,但是如果重力
because gravity acts on them, but if gravity
作用于所有的东西上为什么不是所有的的东西都沉没
acts on everything, why doesn’t everything sink?
想象一个潜艇在水下静止
Imagine a submarine that is stationary underwater.
我们知道重力作用于它,但潜艇不下沉。
We know gravity is acting on it, but the sub isn’t sinking.
所以这里一定有一个反重力。
So there must be a force opposing gravity.
我们称之为浮力。
We call this force buoyancy.
在这个视频中,我们将研究浮力以及为什么一些东西
In this video, we will examine buoyancy and why some things
在其他东西不漂浮的时候漂浮
float while others don’t.
首先,在开始浮力之前让我们回顾一下密度
First, let’s review density before we move on to buoyancy.
不同的材料有不同的密度。
Different materials have different densities.
它是在给定体积内有多少质量的一个值
It’s a measure of how much mass there is at a given volume,
并且由以下公式决定
and it’s determined by the following formula.
密度=质量÷体积
Density equals mass divided by volume.
密度是一种固有特性
Density is an intrinsic property,
这意味着它取决于材料
which means it depends on the material
而不是物体的形状或大小。
but not the shape or size of the object.
所以尽管一条金条重量超过一枚金币
So while a gold bar may weigh more than a gold coin,
它们仍有相同的密度
they have the same density.
而且,虽然一千克的石头和一公斤羽毛
And while a kilogram of rocks and a kilogram of feathers
有相同重力,但它们有非常不同的体积
have the same weight, they have very different volumes
因此它们有非常不同的密度
and therefore very different densities.
一般来说,岩石和金属密度比水大然后下沉
Generally, rocks and metals are more dense than water and sink
而塑料和木材
while Styrofoam and wood are less
密度比水小并且漂浮
dense than water and float.
所以我们看到密度影响浮力,
So we see that density affects buoyancy,
但它不可能是万能的。
but it can’t possibly be everything.
许多现代船舶是由上吨的金属做的
Many modern ships are made of tons of metal
他们密度比水大,但船只仍然可以漂浮
that are more dense than water, but the ships still float.
船只漂浮着是因为它们并不只是
The boats are floating because they are not just
一块金属固体
a solid block of metal.
他们的外壳是金属做的,但里面
Their hull is made of metal, but the inside
充满了空气以及人们和货物的空间。
is full of air and room for people and cargo.
船的所有内部空间
The ship with all the space inside
排开巨大体积的水
displaces a greater volume of water
如果它被挤压成一块,在这种情况下
than if it were squished into a block, in which case
它实际上会下沉
it would actually sink.
因此,我们现在知道,被物体排开的液体的体积
Therefore, we now know that the volume of the fluid displaced
和流体的密度
by the object and the density of the fluid
在定义浮力中起作用
play a role in defining buoyancy.
考虑到这一点,让我们仔细看看
With this in mind, let’s take a closer look
事物实际上是如何漂浮的
at how things actually float.
我们将三个完全相同的木块放入
Here we are placing three identical wooden blocks
三种不同密度的液体
and three liquids with different density.
液体是蜂蜜、水和外用酒精。
The liquids are honey, water, and rubbing alcohol.
注意到液体密度越大
Notice how the more dense the liquid is,
木块漂浮得越高
the higher the block floats.
因此我们看到液体密度作用于浮力的重要性
Hence we see the importance of the liquid density
因此我们看到液体密度作用于浮力的重要性
on the buoyancy.
并且注意到了木块漂浮得越高
Also, note that the higher the block floats,
越小体积的液体被排开
the less liquid volume is being displaced.
这同样演示了排开的(流体)体积是如何
This demonstrates how the displaced volume plays
作用于浮力的
a part on buoyancy as well.
所以到目前为止,我们知道浮力反重力,
So up to now, we know that buoyancy opposes gravity,
浮力取决于流体的密度
buoyancy depends on the density of the fluid,
以及浮力取决于漂浮物体在水下的体积
and buoyancy depends on the submerged volume
漂浮物体在水下的体积
of the floating object.
阿基米德,一个古希腊科学家
Archimedes, an ancient Greek scientist,
发现浮力与流体密度
found that the buoyancy force is proportional to the density
和被物体排开的流体体积成正比
of the fluid and the volume of the fluid displaced
和被物体排开的流体体积成正比
by the object.
如果浮力大于
If this buoyancy force is greater
作用于物体上的重力
than the gravitational force acting on the object,
物体漂浮
it floats.
浮力的精确公式是
The exact equation found for a buoyancy force is given by fb
Fb等于D乘上g乘上VFb是浮力
equals D times g times V. Where fb is the buoyancy force,
D是流体密度,g是重力加速度
D is fluid density, g is gravitational acceleration,
而V是被排开(流体)体积
And V is displaced volume.
让我们用阿基米德方程求出
Let’s use Archimedes equation to figure out
一艘货船可以携带重量多少的东西
how much weight a cargo ship can carry.
我们的货船长250米,宽30米,
Our cargo ship is 250 meters long, 30 meters wide,
在水下十米处走
and goes 10 meters below the water’s surface.
把这些乘起来,我们知道
Multiplying these together, we know
被货船排开的(液体)体积
the volume displaced by the cargo ship
是75000立方米
is 75,000 cubic meters.
把他们与水的密度和重量加速度相乘
Multiply them by the density of water
把他们与水的密度和重量加速度相乘
and gravitational acceleration, we
我们得到作用于船的浮力
get that the buoyancy force acting on the ship
是7.35亿牛,约1.65亿镑
is 735 million newtons, or about 165 million pounds.
这意味着这艘船在下沉前能容纳1.65亿磅的重量
That means that the ship can hold 165 million pounds
这意味着这艘船在下沉前能容纳1.65亿磅的重量
of weight before it sank.
这相当于8000头大象,甚至170
That’s the equivalent of 8,000 elephants or even 170
架大型客机
jumbo jets.
我们也可以利用浮力来解释
We can also use buoyancy to explain
一些你可以在家里尝试的有趣的实验
some interesting experiments that you can try at home.
例如,其中一个是新鲜的
For example, one of these is fresh
而另一个是意外地遗忘在冰箱外的
and one was accidentally left out of the refrigerator.
我们如何用浮力找出哪个是哪个?
How can we use buoyancy to figure out which is which?
嗯,一个是漂浮的,一个是下沉。
Well, one floats and one sinks.
发生了什么
What’s going on?
这是有点棘手。
This is a bit tricky.
虽然蛋壳看起来很结实,但实际上它们多孔的。
While eggshells look solid, they’re actually porous.
这意味着,外壳覆盖着一些小洞
That means that the shell is covered in small holes.
随着时间的推移,当蛋开始摇晃
Over time, as the egg starts to rock,
蛋液通过这些小孔离开
the egg’s liquid leaves through these holes
然后被空气取代
and it’s replaced by air.
当这种情况发生时,鸡蛋的体积
When this happens, the volume of the egg
保持不变而鸡蛋的质量减少
stays the same while the egg’s mass is decreasing.
因此,密度变小
Therefore, the density decreases.
充足时间后,蛋的密度
After enough time, the egg’s density
变得小于水的密度
becomes lower than the water’s density,
而蛋也开始漂浮
and the egg starts to float
这是另一个你可以试着在家里做的实验。
Here’s another experiment that you can try at home.
当你将葡萄干放入苏打水,会发生什么
What happens when you drop raisins into soda?
有时他们在玻璃杯底部
Sometimes they’re on the bottom of the glass.
其他时候,他们在顶上
For other times they’re at the top.
发生了什么
What is going on?
苏打水有二氧化碳气体,它们以泡泡的形式逃走
Soda has carbon dioxide gas, which escapes as bubbles.
葡萄干的密度比水打而(它们)也一开始就下沉。
Raisins are more dense than water and initially sink.
因为葡萄干有皱纹的表皮
Since raisins have wrinkled skin,
所以当他们试图逃跑,泡泡就可以被捕捉在表面
the bubbles can get trapped on the surface
所以当他们试图逃跑,泡泡就可以被捕捉在表面
as they try to escape.
这些泡泡在水中上浮
These bubbles are buoyant in water
因为他们的密度低,(并且可以)使葡萄干漂浮
because they’re low density and cause raisins to float.
葡萄干到达表面后
After the raisins reach the surface,
泡泡爆破而葡萄干再次下沉
the bubbles pop and the raisins sink again.
这个过程重复,而葡萄干(像)跳舞(一样)
This process repeats, and the raisins dance.
而这就是浮力
And that’s buoyancy.

发表评论

译制信息
视频概述
听录译者

收集自网络

翻译译者

收集自网络

审核员

自动通过审核

视频来源

https://www.youtube.com/watch?v=bNIwWx3sWkc

相关推荐