General Science GK Questions with Answers – Page 16

In a wheelbarrow the wheel is the fulcrum, the load in the tray lies between the wheel and the hands, and the effort is applied at the handles, so the load sits in the middle, which defines a second class lever; a nutcracker, a bottle opener and a lemon squeezer…

In stable equilibrium the original position is the one of least potential energy, so a small displacement lifts the centre of gravity and the weight of the body brings it back, as with a cone resting on its base or a book lying flat on a table.

A zero net force gives translational equilibrium, so the body as a whole does not accelerate, and a zero net torque gives rotational equilibrium, so it does not begin to spin; complete equilibrium requires the two together.

Torque is the product of the force and the perpendicular distance of its line of action from the axis, so the same turning effect can be produced by a smaller force if that distance is made larger; a long handle therefore does the same work with less effort.

The magnitude of torque is r into F into the sine of the angle between the arm and the force, and the sine of an angle is largest, equal to one, at 90 degrees, so the whole of the force is then used in turning the body.

The centre of gravity is a geometrical point through which the resultant weight of a body acts, and by symmetry that point for a uniform ring is its geometrical centre, which lies in the empty space inside the ring.

When three forces are represented by the sides of a triangle taken in order, their vector sum is zero, because the three sides close the triangle, so the body cannot be pushed away; but the lines of action are different, so the system reduces to a couple.

Torque is the product of a force and the perpendicular distance of its line of action from the axis of rotation, so its unit is the unit of force multiplied by the unit of length, the newton metre, and its dimensional formula is M L squared T to the power…

In it nitrogen from the air and hydrogen from natural gas combine directly over a finely divided iron catalyst at high pressure and a temperature of about 450 to 500 degrees Celsius; the ammonia produced is then reacted with carbon dioxide to make urea.

Muriate of potash is potassium chloride, carrying about sixty per cent potash, and it is the cheapest and most widely used source of potassium for crops; the old word muriate simply means a chloride.

Nobel made the dangerously sensitive liquid nitroglycerine safe to transport and use by absorbing it in kieselguhr, a porous earth, and patented the resulting dynamite in 1867; he later combined nitroglycerine with nitrocellulose to make blasting gelatin, and the fortune from these patents endowed the Nobel Prizes.

Gun powder, also called black powder, is made of roughly seventy-five parts potassium nitrate or saltpetre, which supplies oxygen, fifteen parts charcoal, which is the fuel, and ten parts sulphur, which lowers the ignition temperature and speeds the burning.

Replacing part of the soda and lime of ordinary glass with boron trioxide gives a glass whose coefficient of thermal expansion is very low, so it does not crack when heated or cooled suddenly; that is why laboratory beakers, test tubes and ovenware are made of it.

Metal oxides dissolved in molten glass absorb part of the visible spectrum, and cobalt oxide is the standard colourant for the deep blue of bottles and decorative glass, effective in very small quantities.

Cement needs one calcareous material, limestone, for its lime, and one argillaceous material, clay or shale, for its silica, alumina and iron oxide; the mixture is burnt in a rotary kiln at about 1450 degrees Celsius to give clinker, which is then ground with gypsum.

About two or three per cent of gypsum, which is calcium sulphate dihydrate, is ground with the clinker because it slows down the hydration of tricalcium aluminate, the compound that would otherwise set almost the moment water was added and leave no time to place the concrete.

Farmyard manure is the decomposed mixture of cattle dung, urine and bedding litter, and in general it carries only about half a per cent of nitrogen, along with roughly the same order of phosphate and potash.

Nitrogen, phosphorus and potassium are the three primary nutrients, and a fertiliser that carries two or more of them in one chemical compound is called a complex or mixed fertiliser; diammonium phosphate, which supplies both nitrogen and phosphate, and the NPK grades sold by number are the familiar examples.

Superphosphate of lime is made by treating rock phosphate with sulphuric acid, and the nutrient it supplies is phosphorus in the form of available phosphate, not nitrogen; it is therefore a phosphatic fertiliser.

For a real object anywhere in front of it, a convex mirror always gives a virtual, erect and diminished image.