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Explore Mars in 3D – Watch this Video

To watch this 3D videos exploring the surface of Mars, you will need a set of 3D glasses (Magenta Cyan / Red Blue)

How does a microwave oven work?

Now, microwave oven is so popular that majority of houses have one. Many use it mainly to reheat food without loss of nutrient. The advantage is that the microwave heats up the food very fast.

Some observations made on microwave oven are,

  • It does not heat up the vessels directly
  • It is not able to cook food contained inside metal vessels
  • If the turn table does not work, cooking will not be even.

 

So, it is pertinent to ask how the mechanism of heating in a microwave oven is different from other heating devices?

Here the water molecules, which are polar in nature play the magic. (A polar molecule is one in which the centre of mass of positive charges and the centre of mass of negative charges do not coincide and have a net dipole moment.) When microwaves are passed through food materials, the water molecules contained in them tends to turn and this rapid churning of water molecules develops a lot of heat. The turn-table adds to the churning and randomization developing heat more rapidly.

The food materials contained in a closed metal vessel will not be heated up by the microwave oven as they do not allow microwaves to pass through them. The metals are opaque to microwaves.

Why the food materials heated using microwave dry up and become stiff when cool?

In a microwave oven, the water molecules are heated very fats that the water is converted readily into steam. If kept open, the steam will escape and the material will become hard when cooled due to the decrease in the water content.

when no light is present so why do we see black colour ?

When no light is present so why do we see black colour ?

Praveen Kumar asked

Answer:

Black is not the color, it just denotes the absence of light.

When there is light, an object is seen black when it absorbs all light incident on it.

What is Lidar?

LIDAR stands for LIght Detection And Ranging.

LIDAR measures the vehicle’s speed by sending out two laser pulses and calculating the difference in time it takes to detect the pulses of light reflected from the target, your car.

LIDAR has the distinct advantage of being able to pick out one vehicle in a cluttered stream of traffic; your vehicle cannot be mistaken for another vehicle unlike radar, which has a broader pulse. It can also be used over a large distance, which makes it even more difficult to spot. License plates are typically the strongest LIDAR target, as they are covered in a retroreflective material that returns light back its source with a bare minimum of scattering.

The LIDAR system can determine your speed very quickly, about 1,000 times per second!

For more details please visit http://www.physicscentral.com/explore/poster-speed.cfm

 

A question from Dynamics

The constant force that works in the object M=5 kg forces the object with mass m=4 kg to move with acceleration a=2 m/s^2.
The coefficient of friction between M and the table is 0.2.
Determine
a)F=? b) T=?

 

Elumna asked this

The First Android App from AskPhysics – gCalc

AskPhysics is now concentrating on releasing a series of useful apps for android devices.

The first in the series is gCalc

“An Android app which when supplied with the weight of a body on earth can find the weight on other planets, moon, and dwarf planets.”
The author of the App is Mr. Vishnu – A fan of Physics (and askphysics too) and Android apps.
You can download the app and then
1.) Make sure if Install from Unknown Sources is enabled.
(Settings –> Applications –> enable “Unknown Sources”
2.) open the downloaded file
3.) Accept and Install.
4.) Open the app ( gCalc in the Menu)
Click Here to Download the app (If you are browsing from pc, you can later transfer it to your android device and install.)
See below a screenshot of the app.

Doubt in Law of Gravitation

Newton's law of universal gravitation for two ...
Newton's law of universal gravitation for two bodies. This law governs gravitational forces in the Earth. (Photo credit: Wikipedia)
Colorized engraving after Enoch Seeman's 1726 ...

According to law of gravitation
F=g*(m1*m2)/r^2
If we bring two objects close to each other say our hands then the distance will be zero and the force of attraction will become infinite because r will we zero. Therefore F will become infinite but this is not the case.
When we touch our both palms together we can easily pull then away.

Asked Ankit Sharma

Answer

When we consider the distance, it is between the center of mass of the two bodies under consideration. When we bring our hands together the distance between their CM is not zero.

Other wise, the two particles under consideration must be point masses.

Then if you consider two atoms or two nuclei, the forces that come into play will be different if we decrease the distance between two atoms or nuclei. The attraction will turn into strong repulsion when the limits are exceeded.

 

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