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Welcome back to the fort, for more cool science about forts and forces!
欢迎回到沃斯堡，我们有很多关于堡垒和力的有趣科学知识！
Last time, we showed you how to build a sheet fort, using a bedsheet, some books, and a couple of chairs
上次，我们向你展示了建造床单堡垒的方法，所用的材料是床单、一些书、几把椅子
or just a nice, long piece of string.
或一段结实的长绳。
Those forts were possible thanks to tension, the force that happens when we pull something tight.
这些堡垒能成功要多亏拉力，即我们拉紧某物时产生的力。
By putting tension on the sheet, we were able to turn it into a roof for our fort and an indoor tent!
通过床单上的拉力，我们能把它做成堡垒的房顶和室内帐篷！
But tension is not the only force you can use to build a fort!
但拉力不是我们建造堡垒使用的唯一的力！
A force called compression comes in pretty handy, too.
压力也很有用。
While tension is the force of something being pulled tight,
拉力是物体被拉紧时产生的力，
compression is the force that happens when things are pushed together.
而压力是物体被挤压在一起时产生的力。
Think of squeezing a spring in your hands.
想想你手捏一个弹簧。
You squish it together by putting pressure on it. That's compression.
你给它加压，把它挤压在一起。这就是压力。
The same thing happens when you put pressure on, say, a chair when you sit on it.
同样的事也发生在你坐椅子的时候。
The legs of the chair get squeezed between the seat of the chair and the floor.
椅座和地面之间的椅腿受到了挤压。
We can't see the compression in the chair legs the way we do when we look at a spring being squeezed...but it's there!
椅腿所受的压力达不到弹簧受挤压时产生的效果，我们看不到，但它确实存在！
Now, what do you think would happen if the chair's legs weren't strong enough to handle all of that compression?
现在，你想如果椅腿不够壮，承受不了所有的压力会怎么样？
Well you might end up on the floor because the legs would break!
你可能会坐到地上，因为椅腿折了！
That's why we make chairs out of metal and wood, instead of, say, raw spaghetti.
这就是我们用金属和木头做椅子，而不是用生意大利面条的原因。
Although tasty, noodles wouldn't be able to stand up to the compression that happens when you sit on the seat.
尽管面条美味，但承受不住你坐到上面的压力。
OK, but let's get back to fort-building!
好了，我们回到建堡垒的话题上！
Now that we know what compression is, how can we use it to build a fort?
现在我们知道了什么是压力，那么我们如何用它建堡垒呢？
First, we need to pick materials that will be able to be stand up under pressure.
首先，我们需要挑选能够承受住压力的材料。
So, spaghetti is out of the question!
所以，意大利面肯定不行！
But what about those chairs that we used to build the sheet fort?
那么我们用于建造床单堡垒的椅子可以吗？
This time, try setting them up so the seats face each other, and leave some space between them.
这次，试着把它们面对面摆放，中间留些空间。
Now just plop a sofa cushion on top of the seats.
现在把沙发垫放在座位上。
Even though we can't see it, the legs of the chairs are getting compressed just a little bit.
椅腿正被压缩，即使我们看不到。
They're strong enough to hold up the weight of the cushion
它们很强壮，能承受住沙发垫的重量，
so we have a nice little tunnel to lead into our fort.
所以我们建成了通往堡垒的小隧道。
But we can also use cushions and compression to build the walls of our fort.
但我们也可以利用沙发垫和压力建造堡垒的墙壁。
This part is a two-person job, so you might want to get help from a parent,
这是两个人的工作，你可以寻求父母、
a brother or sister, or whoever you want to share your fort with.
兄弟姐妹或任何你想与之分享堡垒的人的帮助。
You just need to stand up two cushions on their ends,
你只需要在它们的末尾立两个沙发垫，
so they're far enough apart that you can get between them
使两个沙发垫离得够远，你能通过，
but still close enough together that another cushion can reach across the top, to make your roof.
但也要近些，能在其顶部搭另一个沙发垫做房顶。
With one person holding the walls up, the other can balance a third cushion on top, and, Ta-dah!
一个人扶着墙使它们立着，另一个人在其顶上平衡第三个沙发垫，完成了！
The wall cushions are compressed by the roof cushion.
做墙的沙发垫被做房顶的沙发垫压着。
They're being squeezed between the pillow on top and the floor.
它们被压在顶部和地面的枕垫之间。
Now, let's inspect our fort before we go inside!
现在，我们进去之前先检查一下我们的堡垒！
Now, if the pillows that make up your walls are too soft, then they might bend a little.
如果枕垫做得墙太软，它们可能会弯一点儿。
That's the compression pushing down on them and making them curve.
这是施加其上的压力使它们弯曲的。
And if they're really too squishy,
如果它们真得太软的话，
then they won't be able to stand up under the compression that the roof is putting on them.
在房顶的压力下不可能站的住。
And in that case, your fort is just going to collapse.
那样的话，你的堡垒会坍塌。
That might be fun for a second, while all those pillows fall on you.
当所有的枕垫落在你身上的一秒可能会很有趣。
But you're going to have to come up with a better design.
但你要想更好的设计了。
Once you have a fort that you like, and that can stay standing,
你一旦有了喜欢的能够立着的城堡！
You can try adding on to it, using the same ideas, to make it bigger.
你可以用同样的办法往上加东西，使它更大。
Try adding a third wall, or, if you have enough pillows, try making your fort longer!
试着加第三面墙，或者你有足够多的枕垫的话，可以试着加长堡垒！
Now, your fort is good to go!
现在，你要建堡垒了！
Squeaks and I love doing science experiments in our fort.
我和吱吱喜欢在堡垒里做科学实验。
What are you gonna do in yours?
你要在堡垒里做什么呢？
Now you know compression is the force that we cause when we squeeze something,
现在，你知道压力是我们挤压物体时产生的，
and we can use compression to build a fort.
我们可以利用压力来建堡垒。
We just have to make sure that we choose materials that can hold up under the amount of pressure that we put on it.
我们也要保证所选材料能够承受住上面施加的力。
How do you like to make your forts?
你想怎样建造你的城堡？
Do you have a picture of a fort that you're really proud of?
你有引以为豪的堡垒的照片吗？
Or do you have a question for SciShow Kids about, well, anything?
或者你有什么问题要向我们提问吗？
Get an adult's help and let us know by leaving a comment
找个大人帮忙留言
or emailing us atkids@thescishow.com,
或发邮件至kids@thescishow.com，
and we'll see you next time.
我们下期见。
