Luyện nói tiếng Anh bằng Shadowing qua video: Why Cold Drinks Were Deadly Before 1914

In the summer of 1841, Florida doctor John Gorey faced a dire situation.

Yellow fever, also known as the Black Vomit, was sweeping through his town, wiping out entire families.

Patients came to Gorey's small infirmary jaundiced and burning with fevers up to 40 degrees Celsius.

To cool his patients down, Gorey couldn't turn to refrigeration because that hadn't been invented yet.

So he came up with the radical treatment.

He suspended pans of ice in his infirmary, allowing the cool, dense air to flow down over his patients, providing much needed relief.

But this treatment was almost impossible to sustain because it required hundreds of kilograms of ice per day.

And Gori had only one way to get it.

He relied on ice blocks that were transported thousands of kilometers through a now-forgotten ice empire,

A vast network of ships and ice houses all built and controlled by one man.

Known to the world as the Ice King.

Over the previous 35 years, he had forged a monopoly that spanned the globe.

And anyone who wanted ice was at his mercy.

Gori only got a few deliveries each year.

And now, by the peak of summer, the cost of just a few days ice for the infirmary would have been more expensive than the average yearly wage.

So locals began to refer to the ice as white gold.

As Gorey's supply ran out, he was forced to watch his patients suffer and die.

It was in that moment

that he decided he would find a way to free the world from the grip of the ice king.

By the turn of the 19th century, most of America's ice came from the northern states, where thousands of square kilometers of lakes would freeze over for much of the year.

The hard part was getting all that ice out.

To get ice out of a lake or river, first of all you had to trust that it was deep enough to support your weight.

Then there's no way to really tell.

Then you had to walk out several feet onto this plane of ice, take a saw that's as long as I am tall,

and then carve the very ice that you're standing on, and just, you know, hope to heaven that it doesn't sink.

Then you had to kind of float it to shore

and a horse would help to kind of pull the ice into the back of a wagon.

It was frequently common for the harvesters and their horses to fall through into the ice, sometimes to their death.

This dangerous and painstaking process meant that ice remained a rare commodity, available mostly to wealthy landowners.

One of the few who had access to it was 22-year-old Boston merchant Frederick Tudor.

In the winter of 1805, Tudor was thinking back to a tragic incident that had happened four years earlier.

He and his brother came down with a bad fever while visiting the Caribbean.

Back home, they would have just asked their servants to get some ice.

But on the islands, ice was unheard of.

With no way to cool down, the brothers cut their trip short and returned to America.

And while Frederick recovered, his brother did not.

Today we know that ice wouldn't have saved his brother's life, because he likely suffered from a rare case of bone tuberculosis.

But at the time, Tudor believed

that it was the lack of ice on the islands that was responsible for his brother's death.

It was this painful memory that gave him an idea.

What if he could be the one to bring ice to the Caribbean, and in the process, make his fortune?

So Tudor got to work, he hired dozens of men to gather ice, and approached investors to help finance a ship.

But to the investors, this plan seemed ridiculous.

Tudor wrote, people only laugh when I tell them I'm going to carry ice to the West Indies.

Which is understandable, because the journey would take three weeks, sailing through warm seas under the blazing Caribbean sun.

I mean, can you really transport ice in those conditions for that long?

Didn't it all just melt?

It turns out, people had figured out ways to make ice last a long time, even thousands of years ago.

As far back as 500 BC, in the scorching summers of the Persian Empire, ancient kings like Xerxes enjoyed refreshing frozen desserts,

even when the outside temperature climbed as high as 35 degrees Celsius.

Now ice in the desert might seem strange, but during the winter months, temperatures can drop dramatically.

So the Persians filled shallow pools with water which would freeze overnight, and in the morning they would break up the ice sheets and collect the pieces.

To make that ice last until the summer, they used three key techniques.

Let's try a simple experiment.

I have eight ice cubes spread evenly in one dish here,

and I have another eight ice cubes now stacked together in one megacube in this dish over here.

Now if you leave these two plates to melt for a few hours, the stacked ice cubes fare a lot better.

And that's because the main way ice melts is through heat conduction on its surface.

So even though the volume was the same, the surface area exposed here is double what we had here.

The key idea here is that you want to pack your ice as tightly as possible.

In fact, the best shape to minimize the surface area is a sphere.

So if you think about it, a snowman is pretty much mathematically optimal to survive as long as possible.

But you don't need perfect geometry to make ice last a long time.

In the winter of 2010, the city of Helsinki dumped all the snow plowed from their streets onto this huge pile,

around 30 meters high and 100 meters wide.

Almost a year later, that very same pile was still around, despite being exposed to one of the country's hottest summers in decades.

The main reason it lasted so long is

because the ratio of surface area to volume actually decreases for larger and larger amounts of ice.

For example, if you double the radius of this snowman, then the volume of ice increases by a factor of two cubed,

or eight, but the surface area only increases by a factor of two squared, or four.

This is known as the square-cubed law, which was the second technique used by the Persians.

And finally, they needed a way to shield the ice from the harsh desert.

Okay, I have another example.

Two ice cubes, two dishes.

The only difference really is going to be that I have this fan

which is going to be blowing air onto this ice cube.

Now it's not heating any of the air, it's just blowing away any air the ice would have chilled for itself

and it's introducing more warmer ambient temperature air which heats the ice cube better.

After about an hour of the fan blowing this ice cube is completely gone, whereas this one is only about 40% melted.

So obviously you want to minimize the amount of airflow that you're getting around your ice.

One way you can do

that is by putting the ice in a deeper dish like a pit

because colder air sinks to the bottom so it collects around the ice

and lets it stay there for longer and a way you can one-up

that is to seal the ice which is exactly what the Persians did.

This is a yak shawl, an ancient Persian ice house.

It's a massive dome structure with walls up to two meters thick at the base.

Here the Persians collected up to 220 tons of ice and packed it tightly together in a pit.

This allowed the cold dense air to to collect while warm air was funneled up and out of the dome.

After the winter, the entire structure was sealed up, insulating the ice until summer.

For the next 2300 years, these techniques barely changed.

And now Tudor was ready to bet his fortune on these ancient principles.

So he mortgaged land on his family estate to buy a ship

and he began modifying it for the long journey to the West Indies.

He did that by building out a cargo hull in a ship that was built similarly to the ice houses.

The ice was elevated off the ground so it wasn't sitting in meltwater, because meltwater speeds up the melting of ice.

And the blocks of ice were also packed really tightly.

Tudor went all in, sinking a full $10,000 of mostly borrowed money into the venture, which is the equivalent of over a quarter million dollars today.

he sent his youngest brother

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and his cousin ahead to the island of Martinique to build an ice house ready to receive the cargo.

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On the morning of February 13th, 1806, Tudor departed Boston Harbor, carrying with him over 80 metric tons of ice, the first shipment of its kind.

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The Boston Gazette ran an article that read, no joke, a vessel has cleared at the custom house with a cargo of ice.

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We hope this will not prove a slippery speculation.

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After nearly three weeks at sea, Tudor's ship arrived, and to his relief, around half of the ice had survived the trip.

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But there was a problem.

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His brother and cousin had failed to build an ice house.

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So with no place to store the ice, Tudor had to sell it straight off the dock under the hot sun.

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He sold as quickly as possible, but after two days, he had only made about $50.

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The locals were confused by the strange frozen water, and many were shocked when their new product disappeared before their eyes.

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One customer tried to save his precious ice by submerging it in a bath of water, only to find it vanishing even faster.

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In the end, all Tudor could do was watch his remaining ice melt away.

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Yet somehow, he was undeterred, and over the next four years he continued to borrow money, using every cent to ship ice to new markets like Cuba,

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Jamaica, Barbados, and Antigua.

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But business remained difficult.

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Tudor wrote, By 1809, Tudor owed $40,000 to investors,

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which is over a million bucks today.

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He was hounded by creditors, he was forced to hide from sheriffs on his own ships, and he was even sent to debtors prison twice.

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He later described it as the winter of my discontent.

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But during that time, he had a revelation.

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The reason demand wasn't picking up was because the people of the West Indies didn't know what to do with ice.

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So all he had to do, he reasoned, was make them understand by offering them some refreshing drinks.

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He convinces the bartenders there to let him show them how to make icy cocktails.

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And he gives the ice initially to the bartenders for free.

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So the bartenders can sell both the icy drink

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and the room temperature drink at the same price just to see what their customers prefer.

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And lo and behold, they prefer the icy drink.

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In Tudor's own words, a man who has drank his drinks cold at the same

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expense for one week can never be presented with them warm again.

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Tudor even showed them how to make ice cream, which became an instant hit, especially in Cuba.

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150 years later, during the Cuban revolution, its leader Fidel Castro was obsessed with ice cream.

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He was actually known to eat up to 18 scoops after lunchtime.

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Which is a bit crazy.

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His sweet tooth was so famous that the CIA actually tried to assassinate him with a poisoned milkshake.

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Now back in Tudor's day, his work was finally paying off.

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The cafe owners in the West Indies started asking him for more

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and more ice and he realized that he could increase his profits just by refining his methods.

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So he started using sawdust to insulate his ice on the ships

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because sawdust was a phenomenal insulator that you could basically get for free from all the sawmills around Boston.

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They were just trying to get rid of it.

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And he also replaced the manual saws at the lakes with horse-drawn plows, which made it all the easier to get the ice out. Because of

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that, the price of extracting a ton of ice dropped from around 30 cents all the way down to 10 cents.

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By the 1820s, Tudor was finally turning a profit and the ice trade began to pick up, so much so that copycat businesses began to crop up.

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But Tudor wasn't about to let anyone else have a share of the market he created,

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so to maintain his monopoly he often undercut his competition until they either gave up or went out of business.

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Tudor's ambition didn't end there, and he wrote that there was an experiment I have been desirous of making for 20 years.

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In 1833, he took on his biggest challenge yet, a four-month journey to ship ice halfway across the world to Calcutta, India.

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And despite the trip being five times longer than his first one to the Caribbean, more than half of the ice survived.

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In India, the ice was a big hit.

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Over the next 20 years, Tudor made around $220,000 in Calcutta alone, making it one of his most profitable ventures.

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Over that same period, he rapidly expanded his empire, opening routes to Brazil, Singapore, Hong Kong, and even Australia.

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His yearly sales went from less than 10,000 tons in the 1830s to a record high of 132,000 tons in 1856.

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Seeing the wealth and power of his monopoly, the world gave Tudor a new name, the Ice King.

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In under 50 years, the ice trade had become one of the largest industries in the US

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and its second largest export by weight.

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What was once a luxury product became a commodity.

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By the 1860s devices known as ice boxes started popping up in ordinary kitchens.

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Essentially they were insulated wooden cabinets with a compartment for ice at the top

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which would then cool down the food underneath keeping it fresh.

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Businesses across the country soon bought ice daily or weekly, with the average New Yorker buying over 600 kilograms a year.

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This surge in demand resulted in a curious new profession.

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The Iceman.

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The Iceman would go door to door delivering huge blocks of ice up to 45 kilograms.

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And while home delivery was nothing new in the 19th century, the Iceman was unique in that he needed to go inside your house to make his delivery.

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All kinds of rumors and jokes and cultural thoughts started to crop up.

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And if you look at some of the most popular songs at the time, she fell in love with the Iceman or the Iceman took my wife.

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If you look at old Valentine's Day cards that were circulating at this time, they all had puns about the Iceman.

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The Iceman made my wife too hot.

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He was supposed to deliver ice.

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It was so silly.

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Consumption of ice in big cities like New York skyrocketed.

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And by the end of the 19th century, ice had grown into a billion dollar business.

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And while part of the demand was due to home ice boxes, the real driving force was several new industries.

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The ice industry also launched the fish industry, the meatpacking industry, the brewery industry.

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It became like this multi-level industry.

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When we get to the point where there are railroads, then comes the invention of the refrigeration car,

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railroad cars that were insulated with ice blocks to carry things that are perishable.

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So if you think about it, fresh fruits and vegetables that have been region locked now can become national staples.

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So you have apricots and cherries from California, you have strawberries from Florida, they can all go inland.

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Actually, you want to guess the name of a vegetable that was really popularized with these chilled cars?

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Chilled vegetable.

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I'm going to guess lettuce? Which one?

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Iceberg.

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It's got to be iceberg, right?

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Exactly.

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You know, it's like crunchy water, it's like ice, iceberg lettuce.

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It is crunchy water, but it was actually called iceberg because of the ice that kept it fresh.

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This change marked the beginning of a new system called the cold chain.

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And for the meat packing industry, it was a huge upgrade.

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Previously, the only way to transport fresh meat was by sending rail cars filled with live cattle straight from farms to cities.

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Then the animals had to be brought into the city

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and held in local stockyards before they were prepared by local slaughterhouses and butchers.

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The result was that city centers were filled with dirty, noisy cows.

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And on top of that, since almost half of the animal was inedible, shipping was extremely inefficient, pushing up the cost.

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But with chilled rail cars, all this changed, and the country's supply chain reorganized into three parts.

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First, ranches across the Great Plains funneled their cattle to cities in the Midwest.

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Taking on the role of industrial food preparation and distribution, these cities built up vast stockyards, slaughterhouses, and rail hubs to send the meat onward.

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Chicago emerged as the nation's meatpacking capital, ballooning in size from just 30,000 people in 1850 to 1.7 million in 1900.

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And at the end of the chain were the large insatiable cities.

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With the new system in place, almost twice as much edible meat could be transported in each rail car, eventually dropping the cost in urban areas by 39%.

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As a result, demand soared.

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In New York City alone, beef shipments rose from just 2,400 tons in 1882 to around 63,000 tons in 1886.

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That's a 25-fold increase in just four years.

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But more importantly, with a national distribution network to rely on, these cities no longer needed to prepare meat locally.

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They could finally get rid of all the infrastructure and herds of cows in the city center, freeing up the land for things like housing, offices, and factories.

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This fundamentally changed their structure and gave rise to the modern city of today.

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But while the cold chain was redefining America, a new invention was about to overthrow the natural ice industry,

207

which brings us back to Dr. John Gorey in the 1840s.

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A few scientists had devised and even built prototype cooling machines, but they weren't commercially viable.

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And Gori wasn't faring any better.

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He had spent three years struggling to make artificial ice with no success.

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But one night, while experimenting with an air pump to drain a bucket, he noticed that if he let the air expand quickly, it formed a thin layer of ice on the surface of the water.

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He had just stumbled upon the breakthrough he needed, and he set about creating a prototype based on this idea.

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Take a sealed cylinder filled with air and a piston that can move inside it.

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We'll assume there's no friction or heat loss to the environment.

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When the piston pushes down, the air is compressed, increasing its pressure and temperature.

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The reason the temperature increases is because as the piston pushes down, it moves toward the air molecules.

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So when a molecule bounces off this moving surface, it gains a little bit of speed.

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And since the temperature is proportional to the molecules speed squared, Well, the air must heat up.

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But notice that this process is completely reversible.

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If the piston is released, the high pressure air pushes the piston back until the pressure equalizes.

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So now when one of the molecules bounces off the piston, it loses a little bit of speed.

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Gory knew that if he simply let all of this hot high pressure air expand, it would return back to roughly its original temperature, which wouldn't be very helpful.

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But what if he first cooled the air and then let it expand.

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Well then its temperature would drop far lower than the ambient air.

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He started with a similar setup, a cylinder and a piston that were powered by a hand crank, which he then attached to a large air tank.

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As Gorey turned the crank, the piston moved down, compressing the air and raising its temperature.

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To prevent the air from being sucked out of the large tank, Gorey added a one-way valve at the bottom of the cylinder.

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He also added a similar valve at the top of the piston so that the cylinder could refill with fresh air.

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So now with each turn of the crank, more and more air was added to the tank, which allowed Gorey to increase the pressure to around 10 atmospheres.

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But then he added one extra step.

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In between the piston and the tank, he placed a big bucket of water and he forced the air through a submerged pipe.

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This cooled the air down to around the same temperature as the water.

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The result was that his tank was still filled with high pressure air, but instead of being hot, it was cool.

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So now when Gori released some of his cool air into another cylinder with a piston, the air rapidly expanded.

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This cooled the air down below its starting point and dropped it to freezing temperatures.

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Gori then placed this entire cylinder inside a large tank of water, finally making ice.

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But to avoid the entire tank freezing solid and clogging up his machine, he used one final trick.

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Instead of fresh water, he filled the final tank with salt water, which freezes below zero degrees Celsius.

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Since the salt water remained liquid, he then submerged metal molds of fresh water until they froze into solid blocks, essentially creating the world's first ice cube tray.

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For the first time ever, ice could be created anywhere, even in the heat of the Florida summer.

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And when he says to the world, like, I've invented ice, the reaction was, the hell you have.

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You know?

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What?

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No man should be creating ice.

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Only God can create ice.

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And what John Gorey also didn't realize is that in the first public venues in which he announces his ice machine,

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Frederick Tudor has his associates in the audience.

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Frederick Tudor is a man who does not take lightly to threats to his empire.

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And what bigger threat to the natural ice harvesting empire is there than human-made ice?

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There was no way the Ice King was giving up his empire without a fight.

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What he ends up doing is he ends up paying editors up

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and down the eastern seaboard at newspapers to publish scandalous news articles about John Gorey.

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So everywhere from Tallahassee up to New York, you see newspapers publishing headlines like there's this crank that thinks he can make ice as good as God Almighty.

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And ultimately, John Gorey, he does patent his machine, but he never makes a dime on it.

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Gorey spent the next few years in financial ruin.

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A decade later, he died alone and penniless, most likely succumbing to malaria.

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There are reports he suffered an extremely high fever in his final days, the very symptom he had tried to alleviate for so many years.

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But Gorey's invention hadn't been completely ignored.

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Soon others began work on artificial cooling machines, including James Harrison, a Scottish-born engineer working in Australia.

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Harrison noticed that Gori's machine had one big drawback.

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It relied on just two components to move heat, a compressor and an expansion engine.

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So instead of using air to cool his machine, he tried a different approach.

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I have a can of freeze spray here, which is a liquid that when I press down on this button comes out and immediately evaporates into a very,

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very low temperature gas.

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So what I'm going to do is I'm going to blast it at this cup of water

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and the process is actually so effective

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that in essentially under a minute I'm able to get some ice to form in there.

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Okay, so after a layer of water what you get is a bunch of ice.

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Now the reason this works is because something special happens when a substance changes phase.

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So in order to go from a liquid to a gas it needs to absorb a lot of energy

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and pretty much all this energy goes into overcoming the force of attraction between molecules so that they can disperse

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and go into the gas phase.

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Harrison realized he could take advantage of this effect by forcing a fluid to continuously evaporate

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and condense as it's going through a loop.

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A modern version looks something like this.

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Start by adding a liquid under high pressure to a loop.

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Passing this liquid through an expansion valve quickly drops the pressure and temperature, causing some of the liquid to immediately turn into a gas.

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The mixture then passes into an evaporator coil where the remaining liquid continues to boil.

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But this phase change requires a lot of energy, so the liquid absorbs heat from the environment, and this is what creates the cooling effect.

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The cold gas is then cycled through a compressor, raising its temperature, and then it's pushed through a condenser coil.

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Here the hot gas cools and turns back into a liquid, releasing the absorbed heat back into the environment before returning to the expansion valve.

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By repeating this cycle over and over again, Harrison was reportedly able to manufacture as much as 3,000 kilograms of ice per day.

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And his machine was a huge commercial success.

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Meanwhile, public resistance to godless ice and artificial cooling began to fade, overshadowed by a growing health crisis linked to natural ice.

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One of the reasons artificial ice was so much better is because we make it on our own terms with natural ice.

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We had to wait until the right season, in the right place, and then whatever happened in the water that froze, like something died or was rotting in there, you had to work with it.

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By the time we get to the mid-19th century, the peak of the Industrial Revolution, factories and farms just letting loose their chemicals and detritus into the nearby lakes and rivers.

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You put an ice block into your cocktail, you could get cholera up.

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They're like stories of hospitals treating wounds with ice, and then the ice makes you get a disease and your wound isn't even the problem.

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They're getting cholera, they're getting food poisoning or ice poisoning.

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I mean, they're getting very, very sick.

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It's so funny when we were first talking about this story, I was thinking about this, you know, frozen New England ice.

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And I was just imagining like the purest lake water, this crystal clear ice and like just this incredible product, right?

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But now that you mention it, like, yeah, it probably is a lot less hygienic and, yeah, there's probably germs in there.

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And so the, you know, human-made ice companies were like, sure, our ice isn't made by God, but natural ice will kill you.

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So which one do you want?

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After the first affordable home refrigerator landed in the mass market in 1927, it became one of the fastest adopted new technologies of the entire 20th century,

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going from less than 1% of homes having one in the 1920s to 85% by 1944.

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This made its takeoff even faster than the motor car replacing the horse-drawn cart.

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There's this argument of would the world really be so different without refrigeration?

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Like, sure, food, strawberries, iceberg lettuce, but then you think about vaccines, blood donations, insulin, the same cold chain transports, those things things.

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And then beyond medicine, the same principles that Harrison

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and Gore used for their fridges are what allow us to cool things down to almost absolute zero.

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Over the past century, so many of the discoveries that we made rely on this principle of refrigeration.

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MRIs, the Large Hadron Collider at CERN, the James Webb Telescope, all of that is also refrigeration.

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And my favorite is the PCR story where Thermos Aquaticus was in a fridge for 16 years before Carey Mullis discovered it.

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There wouldn't have been that connection to make PCR viable in that way without a fridge.

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I think it's easier to focus on the movement of macroscopic objects and macroscopic things happening,

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but this is really about controlling motion on the smallest scale, controlling thermal motion, which is a pretty remarkable breakthrough.

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I mean, we could heat things up for a long time, so you want to increase the thermal energy of molecules, you could do that from the time we had fire.

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But actually taking those molecules and figuring out how to remove their thermal energy and really slow them down, that's the refrigeration story and that's really recent.

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But as you point out, it has profound effects.

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Gori was able to make ice because he wasn't afraid to step outside his own profession, medicine, and venture into a new field, thermodynamics.

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And while you probably don't need to reinvent the fridge, learning a new skill is always handy.

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You know, here at Veritasium we create simulations

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and models to test our ideas and illustrate them

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and along the way our team has learned to code in Python to make sure our animations are as accurate as possible.

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Từ vựng và ghi chú luyện nói cho bài học này

Bài luyện nói trình độ C1 này dựa trên video “Why Cold Drinks Were Deadly Before 1914”. Video này có 330 câu và 5126 từ để luyện shadowing. Phần lời nói dài 30:08. Người nói nói với tốc độ tự nhiên, khoảng 170 từ mỗi phút, gần với hội thoại hằng ngày. Chỉ 80% số từ nằm trong 3.000 từ tiếng Anh thông dụng nhất, nên từ vựng khá khó.

Từ vựng quan trọng trong video

15 từ khó nhất trong video, kèm phiên âm và nghĩa:

Từ	Phiên âm	Nghĩa
piston danh từ	/ˈpɪstən/	pít tông
cube danh từ	/kjub/	hình lập phương
molecule danh từ	/ˈmɑ.lɪ.kjul/	phân tử
cylinder danh từ	/ˈsɪləndɚ/	hình trụ tròn
iceberg danh từ	/ˈaɪsbɝɡ/	núi băng trôi, băng sơn
kilogram danh từ	/ˈkɪləɡɹæm/	kilôgam, ki-lô-gam
crank danh từ	/ˈkɹæŋk/	giò đĩa
lettuce danh từ	/ˈlɛt.ɪs/	rau diếp
monopoly danh từ	/məˈnɑpəli/	sự độc quyền
melt động từ	/mɛlt/	tan, tan chảy
investor danh từ	/ɪnˈvɛs.tə(ɹ)/	người đầu tư
invention danh từ	/ɪnˈvɛnʃən/	phát minh, sáng chế
meter danh từ	/ˈmitəɹ/	cái đo, người đo
cholera danh từ	/ˈkɑləɹə/	(bệnh) tả
funnel danh từ	/ˈfʌnəl/	phễu, quặn

Cụm động từ bạn sẽ nghe

Từ	Nghĩa
give up động từ	đầu hàng
pick up động từ	nhặt, lượm
break down động từ	hỏng, hỏng hóc
run out động từ	hết

Những câu đáng luyện lại

Các câu ngắn, trọn ý trong video mà bạn có thể dùng lại khi giao tiếp hằng ngày:

Didn't it all just melt?
Let's try a simple experiment.
I'm going to guess lettuce?
I mean, they're getting very, very sick.

Ngữ pháp trong video

Những cấu trúc người nói dùng nhiều nhất, kèm đúng cụm từ trong video:

Cấu trúc	Trong video
Câu bị động be + quá khứ phân từ — nhấn vào việc xảy ra, không phải người làm	been invented · were transported · was forced
Mệnh đề quan hệ who / which + mệnh đề — thêm thông tin về người hoặc vật	anyone who wanted · law, which was · ice which is
Thì hiện tại hoàn thành have/has + quá khứ phân từ — việc đã xảy ra nhưng còn liên quan đến hiện tại	has cleared · have been · I've invented

Phát âm cần chú ý

Người nói dùng 34 dạng rút gọn, ví dụ I'm, wasn't, didn't. Hãy nói theo dạng ngắn đúng như bạn nghe.

Âm “th”: thermal /ˈθɜːməl/, breakthrough /ˈbɹeɪk.θɹuː/
Âm “sh” và “zh”: invention /ɪnˈvɛnʃən/, refresh /ɹɪˈfɹɛʃ/
Từ dài — đặt trọng âm cho đúng: infirmary /ɪnˈfɝməɹi/, monopoly /məˈnɑpəli/, macroscopic /ˌmæ.kɹəˈskɒ.pɪk/, commodity /kəˈmɑdəti/

Những âm người Việt thường gặp khó:

Cụm phụ âm cuối — đọc đủ từng âm, đừng nuốt âm cuối: crank /ˈkɹæŋk/, melt /mɛlt/, invent /ɪnˈvɛnt/, ambient /ˈæm.bi.ənt/, dense /ˈdɛns/
Âm /tʃ/, /dʒ/ và /ʒ/ — tiếng Việt không có, đừng đọc thành “ch” hay “gi”: crunchy /ˈkɹʌnt͡ʃi/, submerge /səbˈmɝd͡ʒ/, vegetable /ˈvɛd͡ʒ.tə.bəl/
Âm /æ/ — mở miệng rộng hơn âm “e”: kilogram /ˈkɪləɡɹæm/, crank /ˈkɹæŋk/, macroscopic /ˌmæ.kɹəˈskɒ.pɪk/, snowman /ˈsnoʊ.mæn/, ambient /ˈæm.bi.ənt/

Cách luyện với video này

Nghe hết video một lần, chưa cần nói, và ghi lại những từ bạn chưa biết.
Bắt đầu ở tốc độ 0,75×, nói đuổi từng câu, rồi quay lại tốc độ bình thường khi đã quen.
Ghi âm giọng mình rồi so với bản gốc, chú ý các từ như piston, cube, molecule.

Phương Pháp Shadowing Là Gì?

Shadowing là kỹ thuật học ngôn ngữ có cơ sở khoa học, ban đầu được phát triển cho chương trình đào tạo phiên dịch viên chuyên nghiệp và được phổ biến rộng rãi bởi nhà đa ngôn ngữ học Dr. Alexander Arguelles. Nguyên lý cốt lõi đơn giản nhưng cực kỳ hiệu quả: bạn nghe tiếng Anh của người bản xứ và lặp lại to ngay lập tức — như một "cái bóng" (shadow) đuổi theo người nói với độ trễ chỉ 1–2 giây. Khác với luyện ngữ pháp hay học từ vựng bị động, Shadowing buộc não bộ và cơ miệng phải đồng thời xử lý và tái tạo ngôn ngữ thực tế. Các nghiên cứu khoa học xác nhận phương pháp này cải thiện đáng kể phát âm, ngữ điệu, nhịp điệu, nối âm, kỹ năng nghe và độ lưu loát khi nói — đặc biệt hiệu quả cho người luyện IELTS Speaking và muốn giao tiếp tiếng Anh tự nhiên như người bản ngữ.

Phương pháp shadowing: đọc hướng dẫn từng bước đầy đủ →

Luyện nói tiếng Anh bằng Shadowing qua video: Why Cold Drinks Were Deadly Before 1914

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