MTEL Physics (69) key terms

The net force on an object equals its mass times its acceleration; equivalently, acceleration equals net force divided by mass. It connects force, mass, and motion in one equation.

The impulse on an object, net force multiplied by the time it acts, equals the change in the object's momentum. Bouncing versus sticking changes the force needed.

If no net external force acts on a system, its total momentum remains constant. This holds in collisions and explosions, even when kinetic energy is lost.

When only conservative forces such as gravity or springs do work, the total of kinetic plus potential energy stays constant; energy converts between forms without being lost.

An object moving in a circle accelerates toward the center with magnitude v squared divided by radius. This acceleration changes the direction of velocity, not its speed.

The turning effect of a force, equal to force times lever-arm distance, or r F sine theta. Its size depends on where the force is applied.

A body's resistance to angular acceleration, determined by its mass and how that mass is distributed around the rotation axis. It plays the role mass plays in linear motion.

Oscillation in which the restoring force is proportional and opposite to displacement, giving sinusoidal motion whose period does not depend on amplitude.

A fluid exerts an upward buoyant force on an immersed object equal to the weight of the fluid it displaces. An object floats when buoyancy equals its weight.

In steady, incompressible, nonviscous flow, faster fluid has lower pressure; the sum of pressure, kinetic, and potential energy terms stays constant along a streamline.

When waves meet, their displacements add. Constructive interference increases amplitude when crests align; destructive interference reduces it when crest meets trough.

A vibration pattern produced by two identical waves traveling in opposite directions. Nodes remain still, antinodes oscillate most, and only certain frequencies resonate.

The change in observed frequency when a wave source and observer move relative to each other; approach raises pitch, recession lowers it.

At an interface, the ratio of sine of incidence angle to sine of refraction angle equals the inverse ratio of indices: n1 sin theta1 = n2 sin theta2.

Light traveling in a denser medium that strikes a boundary beyond the critical angle reflects entirely back into that medium, with no refracted ray escaping.

The spreading and bending of waves around obstacles or through openings, strongest when the opening is about the same size as the wavelength.

The change in a system's internal energy equals heat added minus work done by the system; it is energy conservation applied to thermal processes.

In an isolated system, entropy never decreases spontaneously. Heat flows from hot to cold, and no cyclic engine converts all heat into work.

The maximum efficiency possible for a heat engine between two reservoirs, equal to one minus the cold temperature divided by the hot temperature, both in kelvin.

Energy absorbed or released during a phase change at constant temperature, given by Q = mL, where L is the substance's specific latent heat.

Energy required to raise one kilogram of a substance by one kelvin. Water's high value makes it resistant to rapid temperature change.

PV = nRT relates pressure, volume, moles, and absolute temperature for an ideal gas; it combines Boyle's, Charles's, and Avogadro's relationships.

The electric force between two point charges is proportional to the product of the charges and inversely proportional to the square of their separation.

Force per unit positive charge at a point in space, a vector pointing away from positive charge and toward negative charge; field-line density shows strength.

Potential energy per unit charge at a point, measured in volts. Potential difference between two points drives current through a circuit.

Charge stored per unit voltage for a device, C = Q/V. For parallel plates, capacitance grows with plate area and shrinks with separation.

Current through a conductor is proportional to the voltage across it and inversely proportional to its resistance, I = V/R, when temperature stays constant.

Junction rule: current entering a node equals current leaving, conserving charge. Loop rule: voltage changes around any closed loop sum to zero, conserving energy.

A charge moving through a magnetic field experiences force qvB sine theta, perpendicular to both velocity and field; a charge at rest feels no magnetic force.

A changing magnetic flux through a loop induces an emf equal to the negative rate of flux change times the number of turns.

An induced current flows in the direction that opposes the change in magnetic flux producing it, which follows from conservation of energy.

Light above a threshold frequency ejects electrons from a metal surface almost instantly. Brighter light adds more electrons but does not increase their maximum energy.

The minimum energy needed to free an electron from a metal surface, equal to h times the threshold frequency in Einstein's photoelectric equation.

The wavelength associated with a particle, equal to Planck's constant divided by its momentum; it explains electron diffraction and quantized atomic energy levels.

Atomic model where electrons occupy discrete circular orbits with quantized angular momentum; jumps between levels emit or absorb photons of specific energies.

Mass and energy are interchangeable, described by E = mc squared; a small mass defect releases enormous energy in nuclear reactions.

The time required for half the radioactive nuclei in a sample to decay. After n half-lives, the remaining fraction is one-half raised to n.

Energy needed to separate a nucleus into individual protons and neutrons, equal to its mass defect multiplied by the speed of light squared.

Position and momentum cannot both be measured with unlimited precision; the product of their uncertainties is at least h-bar divided by two.

Moving clocks tick more slowly as measured by a stationary observer, by the Lorentz factor; the effect becomes large only near light speed.