Physics

Physics Definitions Gr12 IEB

vector

a physical quantity that has both magnitude and direction.

scalar

a physical quantity that has magnitude only.

resultant vector

the single vector which has the same effect as the original vectors acting together.

distance

the length of path travelled.

displacement

a change in position.

speed

the rate of change of distance.

velocity

the rate of change of displacement.

weight (Fg)

the gravitational force the Earth exerts on any object on or near its surface.

normal force

the perpendicular force exerted by a surface on an object in contact with it.

frictional force

the force that opposes the motion of an object.

State Newton's first law

An object continues in a state of rest or uniform (moving with constant) velocity unless it is acted upon by a net or resultant force.

inertia

the property of an object that causes it to resist a change in its state of rest or uniform motion.

State Newton's second law

When a net force, Fnet, is applied to an object of mass, m, it accelerates in the direction of the net force. The acceleration, a, is directly proportional to the net force and inversely proportional to the mass.

State Newton's third law

When object A exerts a force on object B, object B simultaneously exerts an oppositely directed force of equal magnitude on object A.

acceleration

the rate of change of velocity.

linear momentum

the product of the mass and velocity of the object

State Newton's second law in terms of momentum

The net force acting on an object is equal to the rate of change of momentum.

State the law of conservation of linear momentum

The total linear momentum of an isolated system remains constant (is conserved).

elastic collision

a collision in which both momentum and kinetic energy are conserved

inelastic collision

a collision in which only momentum is conserved

impulse (J)

the product of the net force and the contact time.

the work done on an object by a force

the product of the displacement and the component of the force parallel to the displacement.

gravitational potential energy

the energy an object possesses due to its position relative to a reference point.

kinetic energy

the energy an object has as a result of the object's motion.

mechanical energy

the sum of gravitational potential and kinetic energy at a point.

State the law of conservation of energy

the total energy in a system cannot be created nor destroyed, only transformed from one form to another.

State the principle of conservation of mechanical energy

In the absence of air resistance or any external forces, the mechanical energy of an object is constant.

State the work-energy theorem

the work done by a net force on an object is equal to the change in the kinetic energy of the object.

power

the rate at which work is done

efficiency

the ratio of output power to input power.

State Newton's Law of Universal Gravitation

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

gravitational field

the force acting per unit mass.

State Coulomb's law in words

Two point charges exert forces on each other. The force is directly proportional to the product of the charges and inversely proportional to the square of the distance between the charges.

electric field

the force per unit positive charge.

potential difference

the work done per unit positive charge.

current

the rate of flow of charge.

State Ohm's Law

The current through a conductor is directly proportional to the potential difference across the conductor at constant temperature.

emf

the total energy supplied per coulomb of charge by the cell.

magnetic flux linkage

the product of the number of turns on the coil and the flux through the coil.

State Faraday's law of electromagnetic induction

the emf induced is directly proportional to the rate of change of magnetic flux (flux linkage).

State Lenz's law

the induced current flows in a direction so as to set up a magnetic field to oppose the change in magnetic flux.

a diode

a component that only allows current to flow in one direction.

threshold (cut-off) frequency (fo)

the minimum frequency of incident radiation at which electrons will be emitted from a particular metal.

work function (Wo)

the minimum amount of energy needed to emit an electron from the surface of a metal.