physical science

Authority

An accepted source of expert information or advice.

Causality

The cause must always precede the effect.

Intuition

The act or faculty of knowing or sensing without rational processes; it involves immediate cognition.

Existence

There exists a physical world separate and distinct from our minds that is knowable through our senses and governed by nature's laws.

Hypothesis

An educated guess based on all the knowledge you have.

Law

A theory so well proven as to be unquestioned.

Occam’s Razor

The simplest explanation that adequately explains the phenomenon is generally correct.

Position symmetry

The laws of nature are the same everywhere in the universe.

Reason

The capacity for logical, rational, and analytic thought.

Self-evident truths

A set of logical and basic assumptions or rules to evaluate our knowledge.

Sensory data

Knowledge obtained through the senses.

Theory

A well-developed set of hypotheses.

Time symmetry

The laws of nature have remained the same through time. They are the same now as in the past and will be in the future.

Principle of noncontradiction

If two contradictory propositions exist, one must be false.

Acceleration

How fast the velocity changes; the change of velocity divided by the time required for the change.

Centripetal acceleration

An acceleration that causes a change in direction.

Force

A push or a pull.

Mass

The amount of matter that makes up an object that determines how much it accelerates when a certain force is applied to it.

Net force

The sum of all the forces present on an object.

Newton’s first law

Every object at rest, or in uniform motion, will remain in that state unless compelled to do otherwise by forces acting upon it.

Newton’s second law

Force = mass × acceleration. Forces cause accelerations. The accelerations are in the same direction as the net force. For the same net force, an object with a smaller mass will experience a larger acceleration.

Newton’s third law

All forces result from interactions between pairs of objects, each object exerting a force on the other. The two resulting forces have the same strength and act in exactly opposite directions.

Unbalanced force

A nonzero net force.

Uniform motion

Motion where there is constant speed and constant direction or when the object is at rest; unaccelerated motion.

Velocity

The speed of a moving object and the direction it is moving.

General theory of relativity

A theory that explains the relationship between the geometry of space and the flow of time in the universe. Mass can warp the geometry of space.

Universal law of gravitation (or law of gravity)

Two objects with mass attract each other with a force of gravity whose strength is proportional to the mass of both objects divided by the square of the distance between the two objects. F = GmM/d 2

Vacuum

A situation where no air friction is present. In other words, there are no contact forces due to air.

Weight

The force of gravity on an object due to another planet-sized object.

Conductor (of electricity)

A substance that easily allows an electric current (electrons) to flow through it.

Contact force

A repulsive force that arises between objects when they touch and is caused by the electromagnetic interaction.

Discrete

Separate or individually distinct.

Domains

A small section in a magnet where the magnetic force from all atoms combines.

Electrical model of matter

All matter contains two kinds of electrically charged particles

Electric force law

Pairs of objects with similar charges repel each other, and pairs with dissimilar charges attract each other, with forces that obey Newton’s third law and can be described by the relationship F = kQq/d 2, where F is the electric force, k is the electric force constant (9 × 109), q and Q are the charges on the objects, and d is the distance between the centers of the two objects.

Electromagnetic interaction

The complete interaction of moving and stationary charges to describe electric and magnetic forces.

Ferromagnetic material

Metals that are permanent magnets or are capable of being turned into a permanent magnet by aligning magnetic domains.

Field line

Lines coming from an object representing the strength of the force.

Friction

Contact forces on the microscopic level. This force slows or inhibits movement.

Insulator (of electricity)

A substance that does not easily allow an electric current (electrons) to flow through it.

Magnetic force

Force exerted by permanent magnets or currents.

Normal force

See contact force.

Pole

A property of magnets—magnets having both a north and south pole at the same time. A single pole doesn’t exist by itself in a magnet. Similar poles repel each other. Opposite poles attract each other.

Semiconductor

Materials with electrical conducting properties. They are in between conductors and insulators.

Archimedes’ principle

An object immersed in a fluid experiences an upward buoyant force caused by contact interactions with the surrounding fluid. The strength of this force is equal to the weight of the displaced fluid.

Buoyant force

An upward force pushing on an object in a fluid.

Convection

Circulation in a fluid caused by temperature and density differences.

Density

How much mass there is in a certain amount of volume—more formally, the object’s mass divided by the object’s volume, density = mass/volume.

Fluid

Anything that flows. Examples include gases such as air and helium and liquids such as water and mercury.

Pressure

How much force is applied to an area, pressure = force/area or P = F/A.

Inertial reference frame

A perspective that is experiencing no acceleration.

Length contraction

Moving objects are shorter in the direction of their motion—this becomes more and more significant the closer the object’s speed is to the speed of light.

Motion symmetry

This is the first postulate of the special theory of relativity. It states that laws are the same for all observers in uniform motion.

Non-inertial reference frame

A perspective that is undergoing an acceleration.

Reference frame

A perspective from which observations and measurements are taken.

Relativity

Motion is only defined relative to other objects, which may have their own motions.

Special principle of special relativity

See motion symmetry.

Special theory of relativity

Based on two postulates, this is the theory of how objects in inertial reference frames behave at high speeds. According to this theory, for moving objects, clocks run slow, length is contracted, and mass increases. Also known as special relativity.

Time dilation

Moving clocks run slow—this becomes more and more significant the closer the object’s speed is to the speed of light.

Angular momentum

An object’s mass times its speed times the radius of the circle on which it is moving.

Conservation of angular momentum

In the absence of a net external torque, the angular momentum of an object (or a collection of objects) is conserved. In other words, the sum of the angular momentum of all the objects in the system will remain unchanged. (This law is always true.)

Conservation of atomic mass number

Total number of neutrons and protons must remain the same. (This law is always true.)

Conservation of charge

The difference between the total amount of positive and negative charges does not change. (This law is always true.)

Conservation of energy

Energy can be neither created nor destroyed. The total amount of energy in the universe never changes. However, energy can change from one form to another, or be transferred from one object to another. (This law is true for all non-relativistic, non-nuclear processes.)

Conservation of leptons

The total number of leptons is conserved. (This law is always true).

Conservation of linear momentum

In the absence of a net external force, the linear momentum of an object (or a collection of objects) is conserved. In other words, the sum of the linear momentum of all the objects in the system will remain unchanged. (This law is always true.)

Conservation of mass

Mass is neither created nor destroyed. Mass may change from one form to another, but the total mass after the transformation is always the same as that before. (This law is true for all non-relativistic, non-nuclear processes.)

Fundamental particles

Basic particles that cannot be broken down into smaller pieces.

Lepton

Electron, neutrino, or electron-like particle such as a muon.

Linear momentum

An object’s velocity times its mass.

Mass number

Number of protons and neutrons.

Quarks

Fundamental particles that make up protons and neutrons.

Chemical potential energy

The microscopic electrical potential energy stored in chemical bonds.

Conduction

A process in which thermal energy is transferred because of a difference in temperature. The objects must touch.

Conservation of mass-energy

The total amount of mass and energy remains the same. Energy can change forms. Mass can be converted into energy and vice versa.

Convection

A process in which thermal energy is transferred by matter moving from one place to another.

Elastic potential energy

The energy stored in the shape of an object such as a spring.

Electrical potential energy

Associated with charge on objects and their position. Bringing two charges of the same sign together increases their electrical potential energy. Bringing two charges of opposite signs together decreases their electrical potential energy.

Gravitational potential energy

Energy associated with an object’s weight and its height. GPE = weight times height.

Kinetic energy

Energy associated with motion. KE = mass times speed squared, divided by two.

Nuclear potential energy

The energy stored in the nucleus because of the strong force between nucleons.

Radiation

A process where thermal energy is transmitted by visible light, infrared radiation, ultraviolet radiation, X-rays, or radio waves.

Thermal energy

Energy associated with temperature.

Work

When energy is transferred or transformed by forces acting on an object.