# Scientific Laws, Rules, and Principles List

The following is a listing of the more common Scientific Laws, Rules, and Principles

First Law of Thermodynamics, also known as Conservation of Energy: the total amount of energy in a system remains constant over time: it is said to be conserved over time. A consequence of this law is that energy can neither be created nor be destroyed: it can only be transformed from one state to another.

The Second Law of Thermodynamics: Energy flows from places of higher concentration to places of adjacent lower concentration. Thus, for example, over time, differences in temperature and pressure tend to even out in a system that is isolated from the outside world, and so heat flows from hotter locations to colder. Scientists describe this in terms of the entropy of an isolated system tending to increase over time.

Newton’s Laws of Motion are not absolutely ‘true’ on very small and very large scales, but they work for all our everyday observations. These three laws state:

• The velocity of a body remains constant unless acted upon by an external force;
• The acceleration of a body is parallel to and directly proportional to the net force and inversely proportional to the mass;
• The mutual forces of action and reaction between two bodies are equal, opposite and collinear (to every action there is an equal and opposite reaction).

The Universal Law of Gravitation: Two objects exert a gravitational force of attraction between them that is proportional to the product of their masses and inversely proportional to the square of the distance between them. It applies to ball bearings just as it applies to planets and stars.

Archimedes Principle: Any object, wholly or partially immersed in a fluid, is buoyed up by a force equal to the weight of the fluid displaced by the object.

Boyle’s law: For a fixed amount of an ideal gas kept at a fixed temperature, Pressure and Volume are inversely proportional. In fact Boyle’s law is one consequence of a more general gas law which states that the product of pressure and volume is proportional to the temperature of a system.

Bernoulli’s Principle: Under ideal conditions the speed of a fluid increases with a decrease in pressure.

Ohm’s law: The electrical current through a conductor between two points is directly proportional to the potential difference across the two points, and inversely proportional to the resistance between them.

Hooke’s Law: Up to a limit the extension of a spring is in direct proportion to the load applied to it.

Snell’s Law, also known as the law of refraction, is a formula which describes the angle of bending when light or other waves pass through the boundary between two different materials, such as water, glass, or air. The formula is not given here but can readily be looked up.

The Doppler effect is the change in pitch you notice when a siren approaches and then moves away from you. When something is moving towards you, the sound waves bunch up closer together leading to an increase in pitch. When something is moving away from you the sound waves are more spread out leading to a decrease in pitch. The Doppler effect also occurs with electromagnetic waves.

The Principle of Natural Selection is that members of a species with characteristics best matched to surviving in their environment will more likely do so, and pass on those traits to their offspring. Natural selection does not in itself account for the origin of the different traits within the members of a species, which is a result of minor statistical variations or mutations. Note however that natural selection does not necessarily give rise to some optimum solution, since it only selects from the alternatives available. And if populations are small there may also be an element of chance involved.

Bernoulli’s Law of Large Numbers. Whilst we may not be able to predict with certainty a single event, such as the death of a particular person, it is possible to predict with great accuracy the average outcome of a large number of similar events.

The Superposition Principle is the concept that when a number of influences are acting on a system, the total influence is the sum of the individual influences. Note that this is only true in what are termed Linear Systems.