a) Thermoplastics and thermosetting plastics:
Thermoplastics:
Thermoplastics can be repeatedly softened by heating and hardened by cooling.Thermoplastic molecules, which are linear or slightly branched, do not chemically bond with each other when heated. Instead, thermoplastic chains are held together by weak van der Waal forces (weak attractions between the molecules) that cause the long molecular chains to clump together like piles of entangled spaghetti. Thermoplastics can be heated and cooled, and consequently softened and hardened, repeatedly, like candle wax. For this reason, thermoplastics can be remolded and reused almost indefinitely. in few words you can say:
1.Thermoplastics can be repeatedly softened by heating and hardened by cooling.
2.Thermoplastic molecules do not chemically bond with each other when heated.
3.examples are Polystyrene and polyethylene .
Thermosetting Plastics: Thermosetting plastics, on the other hand, harden permanently after being heated once.Thermosetting plastics consist of chain molecules that chemically bond, or cross-link, with each other when heated. When thermosetting plastics cross-link, the molecules create a permanent, three-dimensional network that can be considered one giant molecule. Once cured, thermosetting plastics cannot be remelted, in the same way that cured concrete cannot be reset. Consequently, thermosetting plastics are often used to make heat-resistant products, because these plastics can be heated to temperatures of 260° C (500° F) without melting.
In few words we can say:
1. Harden permanently after being heated once.
2. Molecules that chemically bond when heated.
3. Examples are polyurethane and phenolic.
b) Lunar eclipse and solar eclipse:
A lunar eclipse occurs when Earth is between the Sun and the Moon, and Earth’s shadow darkens the Moon. A solar eclipse occurs when the Moon is between the Sun and Earth, and the Sun’s shadow moves across the face of Earth. An eclipse is called a total eclipse if the light is completely blocked or a partial eclipse if the light is only partly blocked.
c) Asteroid and meteorite:
Asteroid, small rocky or metallic body that orbits the Sun. Hundreds of thousands of asteroids exist in the solar system. Asteroids range in size from a few meters to over 500 km (300 mi) wide. They are generally irregular in shape and often have surfaces covered with craters
Meteorite, meteor that reaches the surface of Earth or of another planet before it is entirely consumed by heat and friction from the atmosphere. Meteors and meteorites originate as meteoroids in space. On Earth most meteoroids burn up as meteors before they can become meteorites. Meteoroids also strike bodies in space that lack atmospheres, such as the Moon and asteroids, becoming meteorites without being meteors.
Meteor, bright streak of light caused when a small solid body from outer space known as a meteoroid enters the atmosphere of Earth or another planet and is heated by friction from rapid motion through the air. The outer surface of the meteoroid melts and forms an envelope of extremely hot gas and air that radiates light. The meteoroid may burn up almost completely and fall as dust, or it may fragment or explode in midair. Remains of meteoroids that reach the surface are called meteorites.