Last One Physics

Normal force

The contact force a surface exerts on an object, acting perpendicular (normal) to the surface and directed away from it.

Uniform circular motion

Motion in a circle at constant speed. The speed is constant but the velocity is not, because its direction keeps changing, so the object is accelerating.

Period

The time for one complete revolution (or cycle).

Centripetal acceleration

The acceleration of an object in circular motion, always directed toward the centre of the circle.

Centripetal force

The net force directed toward the centre of a circular path that keeps an object in uniform circular motion.

The Law of Universal Gravitation

Every mass attracts every other mass with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centres.

Coulomb's law

The electrostatic force between two point charges is directly proportional to the product of the charges and inversely proportional to the square of the distance between them.

Electric fields

A region of space in which a charged object experiences a non-contact electric force. Field lines show the direction of the force on a positive test charge: away from positive charges and toward negative charges.

Electric field strength

The force per unit positive charge at a point in an electric field.

Electrical potential energy

The energy a charge has because of its position in an electric field.

A magnetic field

A region of space in which a magnet, a moving charge or a current-carrying conductor experiences a magnetic force.

The generation of a magnetic field by a moving electric charge

Any moving charge produces a magnetic field around its path. Around a straight current-carrying wire the field forms concentric circles, with direction given by the right-hand grip rule.

The force on a current-carrying conductor in a magnetic field

A current-carrying conductor in an external magnetic field experiences a force perpendicular to both the current and the field.

Magnetic flux

A measure of the amount of magnetic field passing through a surface.

Magnetic flux density

The strength of a magnetic field.

Lenz's law

The direction of an induced EMF is such that the magnetic field it produces opposes the change in flux that caused it. This is consistent with conservation of energy: if the induced field aided the change, energy would be created from nothing. Instead, work must be done against the opposing force (e.g. pushing a magnet into a coil), and that work becomes electrical energy.

Inducing an EMF across a moving conductor in a magnetic field

When a conductor of length L moves with velocity v perpendicular to a magnetic field B, the magnetic force (F = qvB) pushes the free charges toward one end. Charge separation continues until the electric force balances the magnetic force, leaving a potential difference (induced EMF) across the ends.

An electromagnetic wave

A transverse wave of oscillating, mutually perpendicular electric and magnetic fields, both perpendicular to the direction of travel.

Frame of reference

A coordinate system from which the position, motion and timing of events are measured.

Inertial frame of reference

A frame of reference that is not accelerating: it is at rest or moves at constant velocity.

Time dilation

A clock moving relative to an observer is measured by that observer to run slower than an identical clock at rest relative to the observer.

Length contraction

The length of an object that is moving relative to an observer is measured, parallel to the direction of motion, to be shorter than its length in its own rest frame.

Work function

The minimum energy needed to remove an electron from the surface of a particular metal.

Mesons

A particle (hadron) made of one quark and one antiquark.