S

Saturated air

Air in which equilibrium exists between evaporation and condensation; the relative humidity is 100 percent.

Saturated solution

The apparent limit to dissolving a given solid in a specified amount of water at a given temperature; a state of equilibrium that exists between dissolving solute and solute coming out of solution.

Scalar

A quantity that has no direction in space, only an amount.

Scientific law

A relationship between quantities, usually described by an equation in the physical sciences; is more important and describes a wider range of phenomena than a scientific principle.

Scientific principle

A relationship between quantities concerned with a specific, or narrow range of observations and behavior.

Scintillation Counter

These devices detect gamma rays and form part of the gamma cameras used in radioactive tracer examinations. Scintillations are flashes of light given out by fluorescent materials (e.g zinc sulphide). When radiation is absorbed by zinc sulphide, it causes the zinc sulphide to produce a small burst of light. These can be electronically counted.

Second law of motion

The acceleration of an object is directly proportional to the net force acting on that object and inversely proportional to the mass of the object.

Second

The second is the SI unit of time.

Secondary coil

Part of a transformer, a coil of wire in which the voltage of the original alternating current in the primary coil is stepped up or down by way of electromagnetic induction.

Second's Pendulum

A simple pendulum whose time period on the surface of earth is 2 seconds is called the second''s pendulum.

Semiconductors

Elements that have properties between those of a metal and those of a nonmetal sometimes conducting an electric current and sometimes acting like an electrical insulator depending on the conditions and their purity; also called metalloid.

Series Circuit

In a series circuit, each component is connected to the other to form a 'chain' between the terminals of the power supply. The rules for current, voltage and resistance in a series circuit are as follows:
Vsupply = V1 + V2 + V3 + ...
Isupply = I1 = I2 = I3 = ...
Rtotal = R1 + R2 + R3 + ...

The mnemonic VISA may help to remember the rules for voltage and current in series and parallel circuits:

VISA: Voltages In Series Add

Shear stress

Produced when two plates slide past one another or by one plate sliding past another plate that is not moving.

Short Circuit

This is one of two types of circuit fault (the other being an open circuit). A short circuit fault is often caused by wires touching, allowing current to bypass a component in the circuit. Short circuit faults register on an ohmmeter with almost zero resistance.

Short-sighted

This refers to a problem with the accommodation ability of an eye. Basically, the eye can focus on near-by objects with no problem, but can't properly focus on far-away objects. This is called myopia. This is because the retina is too far from the lens - so that the focal point falls short of the retina. Short-sightedness can be treated by wearing spectacles which are concave in shape and therefore help to focus the image properly by extending the overall focal length of the glasses and eye.


Sievert (Sv)

The sievert is the SI unit of dose equivalent. Since 1 Sv is a massive dose of radiation, units of microsieverts are often used instead.

Significant figures

Digits that contribute to the accuracy of a measurement.

Simple harmonic motion

The vibratory motion that occurs when there is a restoring force opposite to and proportional to a displacement.

Simple Pendulum

A heavy point mass (actually a small metallic ball), suspended by a light inextensible string from a frictionless rigid support is called a simple pendulum. A simple pendulum is a simple machine based on the effect of gravity.

Sink

A point at which field vectors converge.

SI Units

SI stands for System International. This is the standard system of units used worldwide and includes the metre, the second, the kilogram, the ampere, the kelvin, and the coulomb.

Solenoid

A solenoid is a coil of wire with an electrical current flowing through it. An iron core, inserted into the coil, has the effect of increasing the strength of the magnetic field produced. An increased current or a greater number of turns on the coil will also increase the strength of the magnetic field.

Solar Cell

A solar cell is a photovoltaic semiconductor material which converts light energy into electrical energy. Solar cells are transducers.

Solids

A phase of matter with molecules that remain close to fixed equilibrium positions due to strong interactions between the molecules, resulting in the characteristic definite shape and definite volume of a solid.

Sonic boom

Sound waves that pile up into a shock wave when a source is traveling at or faster than the speed of sound.

Sound

A longitudinal wave which travels through a medium, usually air. Sound also travels through liquids (e.g. water) and solids (e.g. steel). The volume (loudness) of sound is measured using the decibel (dB) scale.

Source

A point from which field vectors diverge; often used more inclusively to refer to points of either convergence or divergence.

Specific Heat Capacity

The energy required to increase the temperature of 1kg of a material by 1 degree Celsius. This is also the energy released during cooling. Water has a high specific heat capacity at 4200 Jkg-1 oC-1. Metals have much lower heat capacities. Physically, this is why metals heat up and cool down more rapidly than water - less energy is required to bring about a given change in temperature.

Specific Latent Heat of Fusion

This is the latent heat per kilogram of material required to change its phase from solid to liquid (i.e. heat energy required to melt 1 kg of material). It is also the heat energy released (in joules) if 1 kg of material 'freezes' from liquid to solid.

Specific Latent Heat of Vapourisation

This is the latent heat per kilogram of material required to change the material's phase from liquid to gas (i.e. heat energy required to boil or vapourise 1 kg of material). It is also the heat energy released (in joules) if 1 kg of material condenses from solid to liquid.

Spectroscope

A device using the diffraction of light to split the visible spectrum up into the rainbow of colours. The spectroscope is used in astronomy to study the spectra of light from the stars.

Spectrum

The electromagnetic spectrum includes all types of electromagnetic radiation(EMR). All types of EMR travel at the same speed: the speed of light, which is 3 x 108 ms-1. Starting with the lowest frequency and longest wavelength radiation, the spectrum consists of:

• Radiowaves
• Microwaves
• Infrared Radiation
• Visible Radiation (red, orange, yellow, green , blue, indigo, violet)
• Ultraviolet Radiation
• X-Ray Radiation
• Cosmic Radiation

The visible spectrum includes red, orange, yellow, green , blue, indigo, violet. Red light has a wavelength of approximately 700 nm and violet light's wavelength is roughly 400 nm. All other colours have a wavelength between these two limits.

Speed

The distance traveled by a body in one unit of time is called its speed. The SI unit of speed is the metre per second.

Speed Time Graph

This is a graph with time plotted along the horizontal axis, and with speed up the vertical axis.

Specular reflection

Reflection from a smooth surface, in which the light ray leaves at the same angle at which it came in.

Spin quantum number

The quantum number describes the spin orientation of an electron relative to an external magnetic field.

Spin

The built-in angular momentum possessed by a particle even when at rest.

Stable equilibrium

One in which a force always acts to bring the object back to a certain point.

Standing waves

Condition where two waves of equal frequency traveling in opposite directions meet and form stationary regions of maximum displacement due to constructive interference and stationary regions of zero displacement due to destructive interference.

State of Motion

When a body changes it's position with respect to a fixed point in it's surroundings then it is said to be in a state of motion. The states of rest and motion are relative to the frame of reference.

State of Rest

When a body does not change its position with respect to a fixed point in it's surrounding, then it is said to be in a state of rest.

Static friction

A friction force between surfaces that are not slipping past each other.

Stator Coil

In a dynamo, the stator coil is the the fixed coil which has an electric current (a.c.) induced in it by the motion of the nearby rotor (permanent magnet).

Steady state

The behavior of a vibrating system after it has had plenty of time to settle into a steady response to a driving force. In the steady state, the same amount of energy is pumped into the system during each cycle as is lost to damping during the same period.

Steam-point

It is the temperature of steam over pure boiling water under 1 atm pressure. The steam point is taken as the upper fixed point (100 deg C or 212 deg F) for temperature scales.

Streamlined

Streamlined objects are designed to reduce fluid drag forces. All rough or angular edges are removed, leaving only smooth curved surfaces. Fish, dolphins, falcons, air interceptors and racing cars are good examples of streamlined objects.

Strong nuclear force

The force that holds nuclei together against electrical repulsion.

Superconductors

Some materials in which, under certain conditions, the electrical resistance approaches zero.

Super-cooled

Water in the liquid phase when the temperature is below the freezing point.

Supersaturated

Containing more than the normal saturation amount of a solute at a given temperature.

System International

Fancy name for the metric system.

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Marwatone.