木曜日は、マリーのはてな日記/Marie the Scientist
Why Are There Rocks under Train Tracks?」
Why Are There Rocks under Train Tracks?
Today, I took a train by myself.
When I arrived at my station it’s started to rain.
The station master walked up to me.
He is my friend.
Do you have an umbrella?
“No, but it’s OK.
I’ll wait for a while.”
“I’m worried the trains will be late because of this rain.”
He was looking at the rail tracks so I looked, too.
Suddenly I noticed small rocks.
Why are there rocks under the train tracks?
“Oh, you want to know about those rocks?
They are called “ballast”.
Ballast is very important for a comfortable train ride.
“I don’t understand.”
“The tracks are on top of rocks.
They are not attached to the rocks.
They just sit on them.
This method of building tracks was first used in England in the 19th century.
It’s an old style but it has many good points.
So it’s still used for railroads around the world.”
“What’s good about it?”
“Thanks to the rocks, trains don’t shake so much.”
“An average train car of today usually weighs about 40 tons.”
“That’s very heavy.”
If train tracks are on the ground, the ground can’t support the weight.
It will sink down.
But when tracks are on the rocks each rock takes a small part of the train’s weight.
So together the rocks can support the train.
The rocks work like a cushion.”
“Rocks are hard but work as a cushion.
Now I understand trains shake less on rocks.”
“Some tracks are not on rocks.
For example, most subways run on concrete.
Then what happens.
Don’t you think they shake more and are rounder?”
“Yes, subways are noisier.
I sometimes can’t hear my friend’s voice on the subway.”
“One reason for that is that subways run in tunnels.
But it’s also because rocks have the power to take in noise.”
“The rocks make trains quiet, too?
“And that’s not all.
When it rains rocks can make water go away from tracks and grass doesn’t grow well on rocks.
So rocks keep the tracks in good condition.”
“Rocks are super cool!”
“But we have to take care of the tracks.
We often check to see if rocks have moved apart.
If we don’t do this, the ride will not be as comfortable.
In the worst case, accidents may happen.”
“Thank you for making the train safe.”
Did you come to pick me up?”
“Yes, I knew you didn’t take an umbrella with you.”
“See you, Marie.”
I learned so much today about railroad tracks.
I’m going to think about rocks in a different way now.