Fundamentals of Physics: Variables, Forces, and Fields

Independent variable: A variable whose variation does not depend on that of another. Commonly denoted by $x$ ; used to study how a dependent variable changes with respect to it. Example: In measuring velocity as a function of time, time is the independent variable and velocity is the dependent variable, often written as $v=f(t)$ .
Dependent variable: A variable whose value depends on another input. Often denoted by $y=f(x)$ ; the outcome you measure in response to changes in the independent variable.

mass ( $m$ ): The amount of matter in an object.
volume ( $V$ ): The amount of space that a substance or object occupies.
water displacement: The pushing aside of water when an object is placed in it (method for measuring volume of irregular objects).
density ( $\rho$ ): The mass per unit volume of a substance, given by $\rho = \frac{m}{V}$ .

frame of reference: A set of criteria or stated values in relation to which measurements or judgments can be made.
force ( $\mathbf{F}$ ): A push or pull upon an object resulting from the object’s interaction with another object.
balanced force: Forces that are equal in size and opposite in direction, resulting in no change in motion.
unbalanced force: Forces that are not equal and opposite, resulting in a change in motion.
inertia: The resistance of any physical object to any change in its state of motion.
static friction: Friction that acts on objects that are not in motion.
kinetic friction: Friction that acts on objects in motion.
drag (fluid friction): The force that opposes the motion of an object through a fluid.
net force ( $\mathbf{F}<em>{net}$ ): The overall force acting on an object; the sum of all forces, i.e., $\mathbf{F}</em>{net} = \sum<em>i \mathbf{F}</em>i$ .
gravity: The force that attracts a body toward the center of the Earth. For an object of mass $m$ near Earth’s surface, the gravitational force is $\mathbf{F}_{g} = m \mathbf{g}$ (where $\mathbf{g}$ is the acceleration due to gravity).
free fall: The motion of a body falling freely under the influence of gravity alone.
orbit: The curved path of a celestial object or spacecraft around a star, planet, or moon.

electric charge: A fundamental property of matter that can be positive or negative.
static electricity: The build-up of electric charge on the surface of objects.
electrical conductor: A material that allows the flow of electric charge.
insulator: A material that does not allow the flow of electric charge.
semiconductor: A material with electrical conductivity between that of a conductor and an insulator.
electrical field: A field around a charged particle where another charged particle experiences a force.

magnet: An object that produces a magnetic field.
magnetic pole: The region where the magnetic force exerted by a magnet is the strongest.
magnetic force: The force of attraction or repulsion generated by moving or spinning electric charges.
magnetic field: The region around a magnet where magnetic materials are influenced.
electromagnet: A type of magnet where the magnetic field is produced by an electric current.
solenoid: A coil of wire that produces a magnetic field when carrying an electric current.
electromagnetic induction: The generation of an electromotive force across a conductor exposed to a changing magnetic field.
In practical terms, a changing magnetic flux drives current in a circuit (EMF).
transformer: A device that transfers electrical energy from one circuit to another through electromagnetic induction.

electric generator: A device that converts mechanical energy into electrical energy.

electrostatic fields - attraction/repulsion: The force between electrically charged objects that causes them to attract or repel each other.