استماع TOEFL B2: The flight of the Bumblebee

Okay!

So, today I am going to talk about the flight of the bumblebee.

Many years ago, scientists believed that the flight of the bumblebee defied the law of physics.

They took the weight of a bumblebee and its wing area into account and did some calculations.

They found, from an aerodynamic point of the view,

the way a bumblebee flies doesn't make any sense.

In fact, scientists believed that bumblebees couldn't even fly.

That's why there is a famous quote, "Aerodynamically, the bumblebee shouldn't be able to fly",

"but the bumblebee doesn't know it so it goes on flying anyway".

Now you must be wondering how come we still see bumblebees flying around amidst the flowers.

It turned out that scientists were wrong.

The big misconception about bumblebee flight is the belief that bumblebees flap their wings up and down.

In addition, the fluid dynamics behind the flight of a bumblebee are different from those that allow a plane to fly.

An airplane's wing forces air down,

which in turn pushes its wing upward.

For bumblebees, it isn't so simple.

They flap their wings back and forth.

As a bumblebee takes flight,

the angle to the wing creates vortices in the air like small hurricanes.

The eyes of those vortices have lower pressure than the surrounding air and suck the wing upwards.

This is what gives the bumblebee the extra bit of lift it needs to buzz around from flower to flower.

It's just like if you move a spoon through a cup of coffee;

you'll see the flow swirl around the sharp edge.

If you move the spoon quickly,

you'll actually see a dimple at the center of the vortex caused by the lower pressure.

Amazing, right?

But this is not what amazes me the most.

What I am most intrigued by is how these bees are able to find the most efficient route between flowers.

You see, bumblebees foraging for nectar in flowers are like salesmen traveling between towns.

Both seek the optimal route to minimize their travel costs.

In order to find out how they achieve this,

a team of researchers conducted an experiment.

They trained the bees to forage nectar from five blue artificial flowers.

Each artificial flower had a yellow landing platform and a single drop of sucrose,

just enough to fill one-fifth of a bumblebee's tank capacity.

This ensured that the bees would visit all five flowers on each foraging route.

The researchers arranged the flowers in a pentagon and spaced them 50 meters apart.

This distance is more than three times as far as bumblebees can see,

so the bees must actively fly around to locate their next target.

A motion-triggered Webcam was attached to each flower to record the bees' visits.

Then, every day for a month, each bee was freed to forage for 7 hours.

At first, the bumblebees visited the flower nearest to their nest,

and then the next closest flower.

It appeared that the bees kept track- that is, they remembered -

the total distance traveled on each foraging trip.

They tried new routes to increase their efficiency,

and if a route was shorter, they used this route instead.

If not, they abandoned it.

As their experience increased,

the bumblebees were able to select the most efficient path to visit the flowers.