Tuesday, April 24. 2018When will a car engine stall?
A car engine will stall-that is to say, it will suddenly stop when you do not want it to - if it is unable to provide sufficient power to overcome the load on the back wheels. This power is provided by the explosion of the petrol and air mixture pushing down on the pistons. If the load on the pistons from the crankshaft is exerting a greater force than that created by the explosion, the pistons will not move down the cylinder and the engine will stop. This can happen if the clutch is engaged too rapidly or if the hand brake is left on. Picture credit: google Tuesday, April 24. 2018What is fire?
Fire is the outward sign that oxygen is combining with other substances in a spectacular chemical reaction. As the air is rich in oxygen, many materials will burn freely in a process scientifically called combustion, if their temperature is raised high enough. This explanation of what had been considered a mysterious phenomenon was discovered by the French chemist Antoine Lavoisier in 1783. The discovery of fire may have changed early man’s wandering mode of life to a more settled one because of an urge to keep the fire burning. It provided him with a new weapon for survival, warmed his cave and huts, enabled him to cook, and helped to scare off dangerous animals. In ancient time’s people in Persia, Egypt and India believed fire to be representative of the sun. Picture credit: google Tuesday, April 24. 2018What makes a Boomerang come back?It is the built-in-skew or twist in a boomerang combined with its spinning motion that makes it return to the thrower. At first people believe that air, pressing on the lower flat surface and passing over the upper rounded face, was responsible for the return flight. But T.L. Mitchell, a Scottish explorer of Australia, gave the true explanation early in the 19th Century. The curved throwing stick is used chiefly by the aborigines of Australia for hunting and warfare. (They also use a non-returning kind of boomerang.) The boomerang is held at one end above and behind the thrower’s shoulder, with the concave edge of the front and swung forward rapidly with the flat side underneath. Just before it is released, it is given extra power with a strong wrist movement. If thrown downward or parallel to the found it sweeps upward to a height f 50 feet or more. When thrown so that one end strikes the found. It ricochets into the air at terrific speed, spinning endwise. It completes a circle 50 yards or more wide and then several smaller ones, up to five, before it drops to the ground near the thrower.
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