Fun Physics: How to find out if an egg is boiled or raw ?

Without breaking the shell, how can we find out whether an egg is boiled or not ?

Mechanics gives us the answer. The whole trick is that a boiled egg
spins differently than a raw one. Take the egg, place it on a flat plate and spin it (Fig. 39). A cooked egg, especially a hard-boiled one, will revolve much faster and longer than a raw one; as a matter of fact, it is hard to make the raw egg even turn. 

The explanation lies in the fact that while a hard-boiled egg revolves as one whole. In a raw egg - the inside liquid do not rotate with the outside shell and so it puts the brake on the egg's motion. 

Also the boiled and raw eggs stop spinning differently. When you touch a spinning boiled egg with a finger, it stops at once. But a raw egg will continue spinning for a while. The reason for this is "inertia" of the liquid inside the raw egg - the liquid of the raw egg still continue moving even after the solid shell is brought to a state of rest. 

Lyrebird: World's weirdest bird that mimics Chainsaw, Car Alarm and More

Lyrebird is found in Australia

Lyre is a musical instrument of ancient Greece. Lyrebird's spectacular tail of fanned feathers, when spread out in display, looks like a lyre.

Lyrebirds are capable of imitating almost any sound. Mixed in with their own calls, clicks and song, you will usually hear them mimicking loud clear sounds made by other birds and mammals - including humans. They have been heard to mimic the sounds of chainsaws, horns, alarms and even trains. They sing throughout the year, and scientists think that the mimicry helps them to vocally set out their territory and defend it from other lyrebirds.

Video: Lyre Bird sings like a chainsaw! 

Video: Lyrebird mimicking children toy gun and other sounds

Now, it is your turn to find out and share one bird that mimics or makes unique and interesting sounds.

Riddle: Who is the greatest of the gods ?

A king was called "Pharaoh" is ancient Egypt. A Pharaoh asked - 
"Who is the greatest of the gods ?"

"I am not" - said Horus (Horus is a god of the sky and kingship)
"Anubis is" - said Isis (Isis is a goddess of health, marriage, and wisdom)
"Isis is lying" - said Anubis (Anubis is protector of the dead)

The Pharaoh knew that only one of the gods is telling the truth - the other two were lying. Who is the greatest of the gods ?

Robotics: How to water proof electronics

This is a continuation of the hydroplane robotics video.

Robotics: Constructing a hydroplane

Templates (source : http://www.rcgroups.com/forums/thumbgallery.php?t=1647267&do=threadgallery&type=files&group=none&starter=no) 

Micro Photography

Micro photography uses a special "micro" lens that captures finer details of an object.

Try to stand up

You'd think I was joking if I told you that you wouldn't be able to get up from a chair provided you sat on it in a certain way, even though you wouldn't be strapped down to it. Very well, let's have a go. Sit down on a chair in the same way the boy in Fig. 13 is sitting. Sit upright and don't shove your feet under the chair. Now try to get up without moving your feet or bending forward. You can't, however hard you try. You'll never stand up until you push your feet under the chair or lean forwards. Before I explain, let me tell you about the equilibrium of bodies in general, and of the human body in particular. A thing will not topple only when the perpendicular from its centre of gravity goes through its base. 







The leaning cylinder in Fig. 14 is bound to fall. If, on the other hand, the perpendicular from its centre of gravity fell through its base, it wouldn't topple over. The famous leaning towers of Pisa and Bologna, or the leaning campanile in Arkhangelsk (Fig. 15), don't fall, despite their tilt, for the same reason. The perpendiculars from their centres of gravity do not lie outside their bases. Another reason is that their foundations are sunk deep in the ground.


You won't fall only when the perpendicular from your centre of gravity lies within the area bound by the outer edge of your feet (Fig. 16). That is why it is so hard to stand on one leg and still harder to balance on a tight-rope. Our "base" is very small and the perpendicular from the centre of gravity may easily come to lie outside its limits.  Porters who carry loads on their heads are well-built a point, I presume, you have noticed. You may have also seen exquisite statues of women holding jars on their heads. It is because they carry a load on their heads that these people have to hold their heads and bodies upright. If they were to lean in any direction, this would shift the perpendicular from the centre of gravity higher than usual, because of the head-load, outside the base and unbalance them. 

Back now to the problem I set you at the beginning of the chapter. The sitting boy's centre of gravity is inside the body near the spine about 20 centimeters above the level of his navel. Drop a perpendicular from this point. It will pass through the chair behind the feet. You already know that for the man to stand up it should go through the area taken up by the feet. Consequently, when we get up we must either bend forward, to shift the centre of gravity, or shove our feet beneath the chair to place our "base" below.