My interview

My interviewee is my professor in my physics class, Shina Tan. He is a Chinese. But he has been America for 12 years. My interview is about his opinion about Chinese universities and American universities. Because he had the experiences both in Chinese universities and American universities.

What was your first expression about the difference between Chinese universities and American universities?
ANS: The first expression was that American universities’ campuses are open while Chinese universities’ surrounded by walls.

What about other difference?
ANS:  Many American universities have long history; Chinese universities don’t have as long history as American universities.

What about the opportunities in the USA and in China?
ANS: American universities are stable, which means competition;Chinese universities are expanding very fast, which means more chances.

What is difference about the relationship between teachers and students?
ANS;In the USA, the relationship is more casual. Students can ask freely. But in China, students don't ask question, in order to show respect to their teachers.

Which country is better?
ANS: It is hard to say which is better. But I am accustomed to American life.  

Graphene

Today, I want to introduce a new kind of material. It is graphene.

Graphene. photo by BAIDU.COM

The material is found in 2004 by Konstantin Novoselov and Andre Geim. They got Nobel prize for the big discover. So you can figure out that how important the material is. But why graphene is important?

In order to understand the importance, we should know the physical structure.Graphene is a kind of  single sheet structure of carbon atoms. It is composed of a carbon atom with sp&sup2 hybrid orbital composition, whose structure is a honeycomb lattice plane film, only one carbon atom two-dimensional layers of material.

The structure determines its unique properties. Graphene is the smallest and the hardest material in the world. It only absorb 2.3% light and the other can go through it. And it is a good conductor for heat and electrons.

 

It is hard to imagine that the material have so many good properties. It already cause a wide research about it. Many applications is experimented now. In the further, our world will be much better with the material that we cannot see by our eyes.

How plane fly

For most people, the reason why planes can fly is not so obvious. Before to understand that, we need to know the Bernoulli principle.

Before further reading, you may interest in an experiment and it will help you to understand the principle better. You prepare two pieces of paper and hold them vertically. When you breath out air into the gap between paper, you will find that the two pieces of paper tend to be close.

According to the experiment, you can conclude that the faster the speed of air, the lower pressure of the air is. The Bernoulli principle says about the mathematical relationship between the velocity of air and the pressure of air. You can watch the video on the top of the blog.

It may be not easy to understand it with out daily common sense. But it does help the plane fly.

How scanner work

Scanners are very useful in our lives. But do you know how do they work? I will make a short introduction of them.

According to the different photosensitive elements, the scanners belong to three different types: CCD, CIS and photo multiplier tube.

CCD is the photosensitive element of our digital cameras. So it is not hard to understand that this type of scanners actually work like cameras. The main difference between camera and scanners is that the scanners only take a picture of  a line of the subject and combine the pictures of different lines into a whole picture of the subject.

CCD(photo by BAIDU.COM)

CIS use photosensitive resistances instead of CCD. The CISs can be very small. But the quality of the picture that the scanners take are very poor when compared to CCD.

Photo multiplier tubes work very different with the other two types. They use the principle that oxide of some material can emit electron when the light beating on them. Another element in the scanners can analysis the electrons flow and get the digit picture of the subject.

Photo multiplier tubes(photo by baidu.com)

What type of your scanners?

Nanomaterials

Nanomaterials, which begin to develop in the 1950s, are a new kind of material. Because of their unique features, they developed very fast and play an important role in modern engineering.

Nanomaterials. This a picture of nanometre flower under the microscope.(photo by BAIDU.COM)

Nanometer material refers to the  materials whose units' sizes are at the nanometer scale range (1-100nm).

The nanomaterials can be classified into 4 types according to the structure of the materials. They are nanometre flower, nanometre fibre, nanometre membrane and nanometre mass.

Even though the new materials do not have a long history, they are widely used now, such as in spaceflights and computers. Many people believe that the new tech is getting more and more important.

If you interest in the field, you can find more information on the Internet.

What is CRT

CRT is short for Cathode Ray Tube. It is true that the technology is out-of-date now. But its principle is quite simple and you may want to make one after you finishing  reading the blog.

CRT. The profile map of CRT. (http://newspaper.li/static/bff350d2a6c72f78100e026098b7e2ad.gif)
Why CRT can display figures?
The high speed electron hit the screen phosphor material to make the lighting.

How to make high speed electron?
Electron guns can produce the electrons.

How we control the figures on the screen?
We take advantage that electron deflect in the magnetic field. If you know how the signal is coded, you can decoding the signal into the magnitude of the magnetic field.

How to make vacuum

It is easy to understand that chemical reactions can reduce the pressure of the air inside a closed volume. For instance, we can burn white phosphorous in a closed container and the air pressure of the container will reduce about 20%.

However, it is not a good enough idea to apply into practice. Because not all the components in the air can participate burning reaction and burning is very dangerous. Maybe white phosphorous is very expensive.

In our practice, we usually use physical reaction instead of chemical reaction to make vacuum. There are two kinds of vacuum pump to make vacuum. The definition 'vacuum' is 'relative vacuum' or 'approximate vacuum'. Actually, the complete vacuum is impossible.

Positive displacement pumps. It is one of the mechanism that can achieve the goal.(make by wikipedia.org)

The first kind is positive displacement pumps. They repeatedly expand the volume of the container, attract gases into the chamber and exhaust the extra gases. If the process goes many times, the air pressure will go down greatly.

The second kind is the Entrapment pumps. The use some material ,like activated carbon, to absorb the molecules. This kind of material work efficiently and cost more.

Of course, there are other kinds of vacuum pumps.

So it sounds easy to make a vacuum pumps by yourself?

Wind Damper

Today, I want to introduce another device. This device is very important to skyscrapers.

Our buildings are get taller and taller. If the building high enough, the people on the top of the building will feel the swaying of the building when the wind is strong.

Wind Damper. A metal ball in the tall building. It can reduce the sway greatly. Without it, you may be afraid of being on the top of buildings.

 

The most important part is the metal ball. They can weigh hundreds of tons  in some buildings.

The principle of the device is that a detector outside the building measures the wind. And it will sent a signal to a specialized computer. Then, the computer will forecast the sway of the building will be and control the ball to sway in the opposite direction to neutralize the oscillation. So the buildings only sway slightly.

Most skyscrapers in the world have install this kind of equipments. Next time you visit a skyscraper, you can take a look at the device.

How do pilot know the speed of plane

 

With the help of modern radio tech, the ground bases can send the planes’ velocity to the pilots. But do you wander how pilots knew the velocity before the radio tech developed. I want to introduce the general idea of the devices which were used to measure the velocity. So people use other methods to measure the speed.

People know that we can measure the angular velocity of wheels which linearly proportion to the velocity. But the plane flies without wheels. They take advantage of the pressure of air.

Pitots.This is the device which can measure the speed of the plane.(photo by Baidu)

 

 

It is pitots that pilots can use to know the speed. Even modern planes have advanced radio devices, most planes still have pitots. It means that the pitots are practical devices.

The device has a hole on the front of the plane. When the plane flies, air will flow into the hole and hit the inductor inside the devices. The inductor can measure the force of crash. The faster the plane flies, the bigger the force is. They have some kind mathematical relation. So pilots can figure out the velocity by knowing the force.

Hot water or cold water freeze first

Is it a question?

 Many people do not think it is a question. Because it is obvious that cold water will freeze first. However, yout intuition falls again. Actually, it is a tough question which is not explained by sicientists. I will introduce this problem in the blog.

A student named Mpemba found that the hot water will freeze first than cold water. He introduced the phenomenon to public. Does his experiment was right?

Actually, many other scientist did it again and got the similiar results. Butall the results were same. There were some other experiments indicated that cold water freezes much faster than the hot water.

So which was right and which is wrong? The scientist did not find the answer. Both of the results are reasonable. The phenomenon had been found about 40 years and still make scientists confused.

But one thing is certain that in some situation hot water will freeze first.

You can do an experiment in your refrigerator. Tell me your result.

Believe your eyes

 

Sometimes, we can determine whether a structure is stable or not from our intuition, even we do not learn any physics ideas. We got that kind of intuition from our daily experience. However, the daily experience can be very tricky. Look at the picture below, do you believe they are really existed or some magics.



 



The answer is they are true.  SURPRISE! OK, let me to explain the principal with the second picture. We consider the hammer and stick is a whole system. The system is stable because it has two equivalent forces: the supporting force of the desk and the gravity of the earth. As long as the two forces are in a line, the system has a chance to be stable. In the second picture, the most mass concerns in the head of hammer. The supporting force exists on the left side of the stick. If we design the configuration, the two forces are in a line. Second, we should consider the rotation of the system. Similarly, we can design the configuration in order to let the stick has a zero torque.

 

So believe your eyes, even though it may unbelievable.