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Squeaks and I are getting ready to visit the fair!
吱吱和我正准备参观展览会!
There’s one around here every year, and there are all kinds of things to do —
这里每年都举办一次展览会，有各种各样的事情可以做——
you can see lots of farm animals, eat some delicious food, and of course, there are plenty of rides!
可以看到许多农场动物，吃美味的食物，当然，还有很多游乐设施!
My favorite ride is the roller coaster.
我最喜欢坐过山车。
But Squeaks was just asking me — and I thought it was a really good question — how roller coasters work.
但是吱吱刚才问我（我觉得这是一个非常好的问题）过山车是怎样运行的。
Because they’re not at all like the cars we drive on the street!
因为过山车根本不同于我们在街上开的车!
Instead, roller coasters have cars that run on a track.
相反，过山车有在轨道上行驶的汽车。
And the way they work is the same reason they’re so much fun: because of forces.
其工作方式和如此有趣的原因是一样的:因为力量。
You can think of a force as a push or a pull on something.
你可以把力看作是对某物的推或拉。
That’s how you make things move, or speed up or slow down!
这就是你如何让事物移动、加速或减速!
For example, bikes start moving when we put forces on the pedals with our legs, which turn the wheels.
例如，当我们用腿用力踩踏板时，自行车就会开始移动，从而带动车轮转动。
And things like cars, planes, and trains work because of the forces made by their motors.
汽车、飞机和火车之所以能工作，是因发动机产生的力。
But roller coaster cars don’t have motors, so the force that starts them moving has to come from somewhere else.
但是过山车没有马达，所以推动它们运动的动力必须来自其他地方。
Most of the time, the force comes from a strong chain attached to the tracks.
大多数时候，力来自于轨道上的一根结实的链条。
The ride starts when the chain pulls the roller coaster cars up to the top of a big hill.
当链条把过山车的车厢拉到一座大山顶时，整个旅程就开始了。
But when the cars start to go over the top of the hill, the chain lets go, and the ride keeps moving anyway, usually all the way to the end!
但是，当汽车开始越过山顶时，链条就会松开，无论如何，整个旅程都会继续，通常一直走到尽头!
That’s because a different force takes over. one you might have heard about before!
那是因为另一种力量在起作用。你可能听说过!
It’s the same force that make a ball fall back down when you throw it into the air.
当你把球抛向空中时，同样的力量会让它掉下来。
Yup, Squeaks!
是的,吱吱！
The force that takes over is gravity.
起作用的力是重力。
Gravity pulls everything on Earth down toward the ground.
重力把地球上的一切都拉向地面。
And it’s gravity that pulls the roller coaster cars down over the hill and along the track.
是重力把过山车沿着轨道拉下山坡。
And once those cars get moving downhill…they can keep going!
一旦这些车开始下坡，它们就能继续前进!
Roller coaster cars that have just gone down a big hill are going so fast that they can get up to the top of the next hill.
刚从一座大山上下来的过山车速度非常快，以至于可以爬到下一座山上。
If they /didn’t/ have enough speed, they wouldn’t make it over the top, and they would just slide back down to the bottom and get stuck there.
如果他们没有足够的速度，就不能爬过顶部，就会滑回底部，卡在那里。
The people who design and build roller coasters know just how fast the cars are going to go… and whether they will be able to get over the next hill.
设计和制造过山车的人知道汽车能开多快，也知道他们是否能翻过下一座山。
And if they find out that the cars don’t have enough speed, they change the design to make sure the cars will be able to get over the top.
如果他们发现汽车没有足够的速度，就会改变设计，以确保汽车能够超越极限。
Or, they sometimes add another chain in the track to pull them to the top of the hill.
或者，他们有时会在赛道上加一条链子，把他们拉到山顶。
Then, once the cars get to the top of that second hill… …gravity takes over again, and pulls them down and to whatever bend or hill comes next!
然后，一旦汽车到达第二个山头……重力就会再次控制它们，把它们拉下来，然后转向下一个弯道或山头!
But even though roller coaster rides can be really fun, they don’t last forever.
不过，尽管坐过山车真的很有趣，但过山车不会永远持续下去。
And that’s because of another kind of force.
这是因为另一种力。
This force is called friction, and it pulls on things that are moving, slowing them down.
这个力叫做摩擦力，摩擦力拉着运动的物体，使运动减慢。
Have you ever tried to slide along the floor in your socks?
你试过穿着袜子在地板上滑吗?
If the floor is made of carpet, your socks scrape along it so roughly that there’s a ton of friction, and you probably won’t slide at all.
如果地板是用地毯铺成的，那么你的袜子就会在地板上刮来刮去，造成很大的摩擦，你很可能根本就不会滑动。
If it’s made of something a little more slippery, like wood, you might slide a little.
如果是用更滑的东西做的，比如木头，你可能会滑一点。
But eventually you stop because there’s friction when your socks scrape along the floor, slowing you down.
但最终你会停下来，因为当你的袜子在地板上刮擦时，会产生摩擦，从而减慢你的速度。
The same thing happens with the roller coaster cars.
过山车汽车也是如此。
The tracks are slippery enough that the cars can slide along them for a while.
铁轨很滑，汽车可以在上面滑一会儿。
But friction is still pulling on the cars, slowing them down, and eventually they stop.
但是摩擦力仍然在拉着汽车，使它们减速，最终它们停止。
So you can use the science of forces to make some awesome rides.
所以可以用力的科学来制造一些很棒的游乐设施。
But all good things must come to an end!
但是，天下没有不散的筵席!
In the meantime, though, we still have a fair to explore!
不过，与此同时，我们仍然有一个公平的探索!
Are you ready to do this, Squeaks?
你准备好了吗，吱吱?
Thanks for joining us!
感谢收看！
If you want to keep learning and having fun with Squeaks and me, hit the subscribe button,
如果你想继续学习并享受吱吱和我的乐趣，点击订阅按钮，
We’ll see you next time, here at the Fort!
我们下次见，就在这个堡垒!
