Kids Research Express

Inertia, the property of matter that causes it to resist any change of its motion in either direction or speed. This property is accurately described by the first law of motion of the English scientist Sir Isaac Newton : An object at rest tends to remain at rest, and an object in motion tends to continue in motion in a straight line unless acted upon by an outside force. For example, passengers in an accelerating automobile feel the force of the seat against their backs overcoming their inertia so as to increase their velocity . As the car decelerates, the passengers tend to continue in motion and lurch forward. If the car turns a corner, then a package on the car seat will slide across the seat as the inertia of the package causes it to continue moving in a straight line. Any body spinning on its axis, such as a flywheel, exhibits rotational inertia, a resistance to change of its rotational speed. To change the rate of rotation of an object by a certain amount, a relatively large forc...

Matter, in science, general term applied to anything that has the property of occupying space and the attributes of gravity and inertia . In classical physics, matter and energy were considered two separate concepts that lay at the root of all physical phenomena. Modern physicists, however, have shown that it is possible to transform matter into energy and energy into matter and have thus broken down the classical distinction between the two concepts (see Mass ; Relativity ). When dealing with a large number of phenomena, however, such as motion, the behavior of liquids and gases, and heat, scientists find it simpler and more convenient to continue treating matter and energy as separate entities. Certain elementary particles of matter combine to form atoms; in turn, atoms combine to form molecules. The properties of individual molecules and their distribution and arrangement give to matter in all its forms various qualities such as mass, hardness, viscosity, fluidity, color, taste, el...

Energy, capacity of matter to perform work as the result of its motion or its position in relation to forces acting on it. Energy associated with motion is known as kinetic energy , and energy related to position is called potential energy . Thus, a swinging pendulum has maximum potential energy at the terminal points; at all intermediate positions it has both kinetic and potential energy in varying proportions. Energy exists in various forms, including mechanical (see Mechanics ), thermal (see Thermodynamics ), chemical (see Chemical Reaction ), electrical (see Electricity ), radiant (see Radiation ), and atomic (see Nuclear Energy ). All forms of energy are interconvertible by appropriate processes. In the process of transformation either kinetic or potential energy may be lost or gained, but the sum total of the two remains always the same. A weight suspended from a cord has potential energy due to its position, inasmuch as it can perform work in the process of falling. An electric...

Heat Transfer, in physics, process by which energy in the form of heat is exchanged between bodies or parts of the same body at different temperatures. Heat is generally transferred by convection, radiation, or conduction. Although these three processes can occur simultaneously, it is not unusual for one mechanism to overshadow the other two. Heat, for example, is transferred by conduction through the brick wall of a house, the surfaces of high-speed aircraft are heated by convection, and the earth receives heat from the sun by radiation. See also Energy ; Heat ; Temperature . Heat can be transferred by three processes: conduction , convection , and radiation . Conduction is the transfer of heat along a solid object; it is this process that makes the handle of a poker hot, even if only the tip is in the fireplace. Convection transfers heat through the exchange of hot and cold molecules; this is the process through which water in a kettle becomes uniformly hot even though only the botto...

Insulation, any material that is a poor conductor of heat or electricity, and that is used to suppress the flow of heat or electricity. ELECTRIC INSULATION The perfect insulator for electrical applications would be a material that is absolutely nonconducting; such a material does not exist. The materials used as insulators, although they do conduct some electricity, have a resistance to the flow of electric current as much as 2.5 × 1024 greater than that of good electrical conductors such as silver and copper. Materials that are good conductors have a large number of free electrons (electrons not tightly bound to atoms) available to carry the current; good insulators have few such electrons. Some materials such as silicon and germanium, which have a limited number of free electrons, are semiconductors and form the basic material of transistors. In ordinary electric wiring, plastics are commonly used as insulating sheathing for the wire itself. Very fine wire, such as that used for th...

Osmosis, in botany and chemistry, the flow of one constituent of a solution through a membrane while the other constituents are blocked and unable to pass through the membrane. Experimentation is necessary to determine which membranes permit selective flow, or osmosis, because not all membranes act in this way. Many membranes allow all or none of the constituents of a solution to pass through; only a few allow a selective flow. In classic demonstration of osmosis, a vertical tube containing a solution of sugar, with its lower end closed off by a semipermeable membrane, is placed in a container of water. As the water passes through the membrane into the tube, the level of sugar solution in the tube rises visibly. A semipermeable membrane that may be used for such a demonstration is the membrane found just inside the shell of an egg, that is, the film that keeps the white of the egg from direct contact with the shell. In this demonstration, the water moves in both directions through the ...

Colloid, suspension of tiny particles of one substance, called the dispersed phase, in another phase, called the dispersion medium. The particles are so small that they remain in suspension indefinitely, unaffected by gravity. Both the suspended, or dispersed, phase and the dispersion medium may be solid, liquid, or gaseous, although the dispersal of one gas in another is not known as colloidal dispersion. An aerosol is a colloidal dispersion of either a solid colloid (such as cigarette smoke) or a liquid (such as insecticide spray) in a gas, the air. An emulsion is a colloidal dispersion of liquid particles in another liquid; mayonnaise, for example, is a suspension of tiny globules of oil in water. A sol is a colloidal suspension of solid particles in a liquid; paints, for example, are a suspension of minute solid pigment particles in an oily vehicle. A gel is a sol in which the suspended particles are organized in a loose, but definite three-dimensional arrangement, giving some rigi...