Basic
Definitions in Physics
Below are some basic definitions in physics that
you are likely to need or come across when studying physics at school.
Speed
Speed is the rate of change of distance.
Velocity
The velocity is the rate of change of
displacement.
Acceleration
The acceleration is the rate of change of the
velocity.
Newton's Laws
1st: Newton's First law
states that every body continues in its state of rest or of uniform motion in a
straight line unless acted on by some external force.
2nd: Newton's Second
Law states that the rate of change of momentum of a body is directly
proportional to external force acting on the body and takes place in the
direction of the force.
3rd: If a body A exerts
a force on a body B, then B exerts an equal and opposite directed force on A.
Linear Momentum
The linear momentum is the product of mass and
velocity.
Force
The force is the rate of change of momentum.
Conservation of Momentum
The conservation of Momentum states that the
total (linear) momentum of a system of interacting bodies, on which no external
forces are acting, remains constant.
Moment of a force
The moment of a force = force x perpendicular
distance from the pivot to the line of action of the force.
Torque of a couple
The torque of a couple or pair of equal and
opposite parallel forces lines of action do not coincide is the product of one
or the forces and perpendicular distance between the lines of action.
Potential at a point
The potential at a point is the workdone in
bringing unit mass from infinity to the point.
Gravitational field
strength
The gravitational field strength is the force
per unit mass.
Charge
The charge is the property of some elementary
particles that gives rise to an interaction between them and consequently to
the host of the material phenomena described as electrical.
Coulombs
The coulomb is the quantity of charge which
passes any section of a conductor in 1 second when a current of 1 Amp is
flowing as given by the equation Q = I x A.
Volt
The volt is the potential difference between 2
points in a circuit when 1 J of electrical energy is converted to other form of
energy when 1 C passes from 1 point to the other.
Resistance
The resistance is the ratio of potential
difference across an electrical component to current passing through it.
Ohm
The ohm is the resistance of a conductor through
which a current of 1 A is flowing when potential difference across it is 1 V.
Electric potential at a
point
The electric potential at a point is the
workdone in bringing unit charge from infinity to the point.
Capacitance
The capacitance is the charge stored per unit
potential difference applied to the capacitor.
Farad
The farad is 1 coulomb per volt.
Magnetic flux density
The magnetic flux density is the force per unit
length per unit current on a current carrying conductor at right angle to field
lines.
Tesla
A Tesla is one weber of magnetic flux per square
meter
The density is the mass of a substance per unit volume.Density
Pressure
The pressure is the force acting normally on
unit area of a surface.
Stress
Stress is the force per unit area of cross
section.
Strain
Strain is the extension per unit length.
Young Modulus
The young modulus is the ratio of stress applied
to a body to strain produced.
Specific Heat Capacity
The Specific Heat Capacity is the heat energy
required to increase the temperature of 1 kg by 1 K.
Molar heat capacity
The molar heat capacity is the ratio of heat
supplied to unit amount of a substance to its consequent rise in temperature.
Specific latent heat
The specific latent heat of fusion or
vaporization is the heat energy required to change the state of 1 kg of
material from solid to liquid or liquid to vapor without change of temperature.
Activity
The activity is the number of disintegrations
per second.
Decay constant
The decay constant is the probability of each
atom of a source decaying in one second (s -1).
Half Life
The half life is the time taken for the number
of atoms of that isotope to decrease to half the initial number.
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