Saturated air:  Air in which equilibrium exists between evaporation and condensation; the relative humidity is 100 percent. 
Scalar Quantity:  A physical quantity, which is described completely by its magnitude. 
Second's Pendulum:  A simple pendulum whose time period on the surface of earth is 2 seconds. 
Semiconductors:  Elements whose electrical conductivity is intermediate between that of a conductor and an insulator. 
Shear strain:  The ratio of the relative displacements of one plane to its distance from the fixed plane. 
Shear stress:  The restoring force developed per unit area when deforming force acts tangentially to the surface of body producing change in the shape of the body without any change in volume. 
Siemens:  The derived S.I. unit of electrical conductance, equal to the conductance of an element that has a resistance of 1 ohm, also written as ohm1. 
Simple harmonic motion:  The vibratory motion that occurs when the restoring force is proportional to the displacement from mean position and is directed opposite to the displacement. 
Snell's law:  The ratio of sin i to sin r is a constant and is equal to the refractive index of the second medium with respect to the first. 
Solenoid:  A cylindrical coil of wire that becomes electromagnetic when a current flows through it 
Sonic boom:  Sound waves that pile up into a shock wave when a source is traveling at or faster than the speed of sound. 
Specific heat:  The amount of heat energy required to increase the temperature of one gram of a substance by 1 . 
Speed:  The distance traveled by a body per unit of time. 
Spin quantum number:  From quantum mechanics model of the atom, one of four descriptions of the energy state of an electron wave; this quantum number describes the spin orientation of an electron relative to an external magnetic field. 
Standing waves:  The waves formed due to superposition of two waves of same frequency and traveling in opposite directions with same speed. 
Steampoint:  It is the temperature of steam over pure boiling water under 1 atm pressure. It is equal to 100 or 212 . 
StefanBoltzmann law:  The amount of energy radiated per second per unit area of a perfectly black body is directly proportional to the fourth power of the absolute temperature of the surface of the body. 
Superconductors:  Some materials in which, under certain conditions, the electrical resistance approaches zero. 
Surface tension:  The property of a liquid due to which its surface behaves like a stretched membrane. 
