Ying Qi pointed to the water tank over there, and Ying Yun slashed it with his fingers, just in time to see a small copper boat-like thing floating on it, and there was a scale next to this water tank.

"If you don't mind, you can watch me listen to my class while eating!" Li Hang said with a smile, the literacy of these boys has been taught, and the rest is some common sense things.

Several people sat around Win Qi and looked at this side curiously.

Li Hang took out a few of the same things. "I have a few things in my hand now, one is a copper ball, this copper ball is the same as the copper ship, but you see, this copper ball has sunk, but the copper boat can float on top of it, why?"

After speaking, Li Hang put down another thing that looked like a bucket.

The students below scratched their heads one by one.

Obviously they are all the same heavy things, why is one sinking in the water, but the other is floating on the water?

"Understood?" Li Hang looked at his apprentice curiously, and then looked at the princes and grandsons on the side.

Obviously, both groups of people are confused.

The bronze boat was big enough to float on the water, but the copper ball, which was a solid copper lump, was made by the craftsman by melting coins.

Zhou Xin on the side was eating popsicles curiously, and then tilted his head to look at Li Hang. "Brother-in-law, could it be that this shape is different?"

Li Hang walked over with a smile and patted her little head excitedly. "It's the shape, I ask you, what is the difference between this copper ball and this copper ship?"

"The copper ball is smaller!"

"The Bronze Ship is bigger!"

A few boys scrambled to speak, and one by one they all suddenly realized their expressions.

"Actually, if you look closely, how much water can be discharged when the copper ball is thrown into the water, and how much water is there in this copper boat?"

As soon as everyone heard this, they immediately understood.

"That's right, whether you can float on the water is not the material of the boat, but the displacement of the boat, which is why you jump into the water, you will feel buoyancy, if you want to drain the water in the water, what do you need to do?"

"Inhale! Swelled! ”

"Paddling!"

A few boys said it intuitively.

"That's right!" Li Hang walked to the front with a smile. "Buoyancy is equal to the volume of the corresponding liquid you discharge, the more you discharge, the greater the buoyancy, so the bigger the stake, the more it sinks, the greater the buoyancy, when it all sinks under the water, it is the most buoyant, and vice versa, the same is true for boats, if you can discharge enough water, you can make the boat float on the water."

The children below looked at Li Hang one by one, their faces extremely strange. "Then if the ship sinks, we just need to find a sampan?"

"Not only the sampan, but you can even prepare some things on the ship early, such as some wooden rings, which can be hung on both sides of the ship on weekdays, but when there is an accident on the ship, you can take these things off to save your life!" The lifebuoy is a stronger running wood in modern times, and in ancient times, it was necessary to find suitable materials, and what was more suitable than wood?

Whether it is a flood, a shipwreck, or falling overboard, this is actually a lot of things that died in ancient times.

Especially when the Yellow River flood has just ended, it is common for there to be two corpses floating on the water.

And the important significance of Li Hang's lesson is to teach these boys how to save themselves, or how to protect their own safety. "Starting tomorrow, you guys will make a lifebuoy yelves! I know it's hot, you boys like to swim in the canals, but everyone has to tie a rope around their waists, and behind the rope they have to hold your lifebuoy! Do you know? ”

"It's the master!" A group of boys are a little distressed, who doesn't know how to water near this canal, won't be.

It's not uncommon to go down to the river to swim in the summer.

"It's for your safety, you know?" Li Hang glanced at the boys, and then looked at Ying Qi on the side.

He has always been only a land general, but he rarely showed a contemplative expression. "Li Xiucai, you said that this boat can float just because the water is discharged, so if you say so, wouldn't it be possible to make a boat with iron and steel?"

"Yes!" Li Hang nodded.

Isn't a small copper boat an example, as long as it is big enough and thin enough? It's just that modern times don't have enough welding technology, and if you want to make that kind of post-modern pure steel warship, that's a dream, not to mention that whether it's seawater or river water, it will cause corrosion to the hull, and this corrosion will cause a lot of waste.

As soon as he heard Li Hang say yes, Win Qi was even more excited.

Li Hang looked at this uneducated guy. "If the sword is not well maintained, if it is not rubbed with oil, it is easy to rust, the main reason is that iron products will absorb water vapor in the air and then react with the air to form rust, you think about it, if it is made of marine iron, it is reacting with water vapor all the time, how long can it last?"

As soon as Li Hang said this, Win Qi instantly wilted like a balloon that had been deflated.

On the contrary, Ying Yun on the side was very interested. "What if it's steel?"

Steel?

In ancient times, there was a saying that 100 pieces of steel were made into steel, but now steel ......

Hehe, before mastering the desulfurization technology, this kind of smelting steel is almost the same as soil steelmaking, and it is basically useless to make coke, after all, the sulfur in the steel made from coal is a harmful element, and firewood is used...... Sorry, the flame temperature is not enough!

"Same!" Li Hang didn't say anything else, but answered the question head-on.

Unless you can cram up stainless steel and all kinds of chemically resistant special steels, it's useless.

What's more, even something like stainless steel may not be much better under long-term corrosion.

After class, Li Hang asked these boys to tinker with the lifebuoy.

Since they like to swim, Li Hang will not stop them, but just get a lifebuoy to provide more protection.

"Master!" The little fat man Hao Jun curiously approached Li Hang. "Last time you said that ice is made of water, why does ice float on the water?"

The little fat man had seen Li Hang's ice water compound more than once. He knew that the stills in the workshop had this thing in them, and now he was curious.

Looking at the little fat man's inquisitive expression, Li Hang waved his hand. "Okay! You go get a buckled clay pot and saltpeter! ”

Filling the clay pot with water, Li Hang glanced at the curious apprentices, then picked up the saltpeter and threw it inside, and then buckled the clay pot.

This is a threaded clay pot, this is the best thing Li Hang thought of to make canned food, and now after the entire clay pot is sealed, this is something to play!

After a while, there was a bang. The clay pot is cracked!

The exposed ice cubes made the princes and grandsons on the side who had never seen hydrated ice look confused.

At this time, the little fat man Hao Jun who was standing on the side suddenly realized that the water would expand when it turned into ice!