MTLE Physics (Grades 9-12) key terms

A physical quantity fully described by magnitude alone, with no direction. Mass, time, temperature, and speed are examples; such quantities combine by ordinary arithmetic rather than vector rules.

A quantity having both magnitude and direction, such as velocity, acceleration, or force. Vectors add by components or geometric methods, and direction changes count as changes in the vector.

The straight-line change in position from start to finish, including direction. Unlike distance traveled, it depends only on endpoints, so a round trip yields zero displacement despite nonzero distance.

The rate at which velocity changes with time, including speeding up, slowing down, or changing direction. Its SI unit is meters per second squared, and it is a vector pointing along the velocity change.

Motion under gravity alone, with air resistance neglected. Near Earth's surface the acceleration is about 9.8 m/s² downward regardless of mass, so all objects dropped together land together in a vacuum.

Two-dimensional motion of an object launched into the air and then subject only to gravity. Horizontal velocity stays constant while vertical motion accelerates downward, so the path is a parabola.

The perpendicular parts of a vector along chosen axes, usually horizontal and vertical. Resolving a vector into components lets perpendicular directions be analyzed independently with ordinary scalar equations.

The single vector that produces the same effect as two or more vectors combined. It is found by tip-to-tail addition or by summing components, and its magnitude is not generally the sum of magnitudes.

An object maintains constant velocity unless a net external force acts on it. Often called the law of inertia, it explains why passengers lurch forward when a bus stops suddenly.

The vector sum of all forces acting on an object. Only the net force determines acceleration; equal and opposite forces cancel, leaving motion unchanged.

The net force on an object equals its mass times its acceleration, written F = ma. For a fixed force, greater mass yields smaller acceleration, linking force, mass, and motion quantitatively.

For every force one object exerts on another, the second exerts an equal and opposite force on the first. These paired forces act on different objects, so they never cancel each other.

An object's resistance to changes in its state of motion, measured by its mass. A more massive object needs a larger force to achieve the same acceleration and is harder to stop.

A measure of the amount of matter in an object and of its inertia, unchanged by location. It differs from weight, which is the gravitational force on that mass and varies with gravity.

The gravitational force exerted on an object, equal to mass times the local gravitational field strength. On the Moon an astronaut's weight is smaller while mass stays the same.

The perpendicular contact force a surface exerts on an object resting against it. It balances the perpendicular component of weight on level ground but changes on inclines or in accelerating elevators.

A contact force opposing relative sliding or the tendency to slide between surfaces. Kinetic friction acts during sliding; static friction adjusts up to a maximum to prevent motion.

A dimensionless number relating friction force to normal force for a pair of surfaces. Typical values are below one, and the kinetic value is usually smaller than the static value.

A sketch showing one object isolated with every external force drawn as an arrow from it. It is the standard tool for setting up net-force equations in mechanics problems.

The net inward force keeping an object moving in a circle, directed toward the center. It equals mass times speed squared divided by radius and is provided by tension, gravity, or friction.

The acceleration of an object moving in a circle at constant speed, directed toward the center. Its magnitude is speed squared divided by radius, and it arises because velocity direction changes continuously.

Motion along a circular path at constant speed. Speed is constant but velocity is not, because direction changes constantly, so the object is accelerating toward the center.

Energy transferred by a force acting through a displacement, calculated as force times displacement times the cosine of the angle between them. Forces perpendicular to motion do no work.

The energy an object possesses due to its motion, equal to one-half mass times speed squared. Because speed is squared, doubling speed quadruples kinetic energy.

Stored energy associated with position or configuration, such as gravitational energy near Earth or energy in a stretched spring. It converts to kinetic energy as the configuration relaxes.

Energy cannot be created or destroyed, only transferred or transformed between forms. In a frictionless system, the total of kinetic and potential energy stays constant.

The rate at which work is done or energy is transferred, measured in watts. One watt equals one joule per second, so a motor lifting a load quickly delivers more power than a slow one.

The product of an object's mass and velocity, a vector quantity measured in kilogram-meters per second. A massive slow truck can have the same momentum as a light fast car.

The product of force and the time interval over which it acts, equal to the change in momentum. Extending collision time with airbags or padding reduces the peak force experienced.

In an isolated system with no net external force, total momentum before an interaction equals total momentum after. This principle explains recoil, collisions, and rocket propulsion.

The turning effect of a force, calculated as force times lever-arm distance from the pivot, with direction given by rotation sense. It depends on where the force is applied, not just its size.

The point representing the average position of an object's mass, where gravity can be treated as acting. An object balanced on a support below this point stays stable.

A condition in which the net torque on a rigid body is zero, so it does not change its rotation rate. Combined with zero net force, it describes a body in complete static equilibrium.

The restoring force of an ideal spring is proportional to its extension or compression and directed oppositely. The constant of proportionality is the spring constant, measured in newtons per meter.

Oscillation in which the restoring force is proportional to displacement from equilibrium. The motion is sinusoidal, and the period depends on mass and stiffness but not on amplitude.

A large-amplitude response occurring when a system is driven near its natural frequency. It can strengthen musical instruments but can also cause destructive structural vibrations.

A disturbance that transfers energy through space without transporting matter. Waves are described by wavelength, frequency, amplitude, and speed, related by speed equals frequency times wavelength.

The number of complete cycles of a periodic phenomenon per second, measured in hertz. It equals one divided by the period and, for a wave, equals speed divided by wavelength.

The distance between consecutive equivalent points on a wave, such as crest to crest. For a wave traveling at fixed speed, longer wavelength corresponds to lower frequency.