Posted in Science & Nature

Shooting Star

When an object from outer space enters the Earth’s atmosphere, it starts to burn up and creates a brilliant streak in the sky, which we call a meteor or shooting star. Contrary to popular belief, this is not due to friction with the air in the atmosphere.

An object entering the atmosphere is typically travelling at extraordinary speeds. Most meteors are travelling around 20km/s (or 72000km/h) when they hit the atmosphere. At these speeds, air molecules do not have a chance to move out of the way. The meteor will instead collide into the air molecules, pushing them closer and closer to each other, compressing the air in front of it.

As we know from physics class, compression increases temperature in gases as per the ideal gas law (PV=nRT). The impressive entry speed of these meteors result in so much air compression that their surface can heat up to 1650 degrees Celsius.

The heat boils and breaks apart the contents of the meteor, turning it into superheated plasma that gives off a glow. This is the streak of light that we see in the night sky when we wish upon a shooting star.

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Posted in Science & Nature

Microwave

The following are some strange things that happen when certain objects are placed in a microwave (and then turned on).

  • Never put metallic objects in a microwave. Metals act as an antenna, collecting the microwave and creating an electric current. This causes the metal to heat up, burning the food or melting plastic containers. Also, if the metal is pointy, it may cause an electric arc (sparks) which can be very dangerous. 
  • Ice alone does not melt in a microwave. This is because microwaves cause vibrations of particles to generate heat, but in ice the water molecules are tightly bonded and so vibration does not occur. 
  • Microwaves can cause something called superheating of liquids. This means that the liquid is heated to beyond its boiling temperature without boiling. A superheated liquid can spontaneously begin to boil in an explosive manner when disturbed. This is dangerous as it can mean that a cup of boiling hot water may suddenly explode in your face.
  • Certain foods are known to generate sparks in a microwave. For example, when two oblique slices of chilli pepper are placed near each other point-to-point, a flame sparks between the two points from the arcing electricity. Grapes do the same thing.
  • Some foods such as grapes and eggs explode in a microwave. This is because of the pressure building up within it from all the steam being released all at once. This is amplified with something like an ostrich egg where the shell is strong enough to contain an immense pressure. But when a certain pressure is reached, the egg will literally explode and send shrapnels of microwave pieces flying out like a bombshell.
  • A piece of garlic will spin rapidly in a microwave as garlic has a thin tube running on one side. As water evaporates, the vapours rush towards both ends causing the garlic to spin. Also, if you cut the bottom of a clove of garlic then microwave it for about 15 seconds, the pieces of garlic will pop out easily.
  • As explained above, metal conducts microwaves and generates a current. This is most obvious when a CD is placed in a microwave, where sparks dance on the surface (assuming the reflective surface is facing up). Similarly, a fluorescent tube will light up in a microwave from the electricity generated.
  • Placing an open flame, such as a lit candle, inside a microwave produces a very strange phenomenon. The naked flame will become ionised plasma and shoot up to the ceiling of the microwave. This is observed as a ball of light floating around. Note that this is extremely dangerous and most likely will destroy the microwave.

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