component 1 Flashcards
Quantity
In S.I. a quantity is represented by a number x a unit,
e.g. m = 3.0 kg
Scalar
A scalar is a quantity that has magnitude only.
Vector
A vector is a quantity that has magnitude and direction
The principle of moments
For a system to be in equilibrium, the sum of anticlockwise
moments about a point = sum of clockwise moments about
the same point.
Centre of gravity
The centre of gravity is the single point within a body at
which the entire weight of the body may be considered
to act
Newtons 1st Law
An object remains in the same state of motion unless a resultant force acts on it
Newton’s 2nd law
The rate of change of momentum of an object is
proportional to the resultant force acting on it, and
takes place in the direction of that force, or f=ma
Newtons 3rd law
If a body A exerts a force on a body B, then B exerts
an equal and opposite force on A.
The principle of conservation of momentum
The vector sum of the momenta of bodies in a system
stays constant even if forces act between the bodies,
provided there is no external resultant force.
Elastic collision
A collision in which there is no change in total kinetic
energy
Inelastic collision
A collision in which kinetic energy is lost.
Work, W
Work done by a force is the product of the magnitude
of the force and the distance moved in the direction of
the force.
Principle of conservation of energy
Energy cannot be created or destroyed, only
transferred from one form to another. Energy is a
scalar.
Simple harmonic motion (shm)
Shm occurs when an object moves such that its
acceleration is always directed toward a fixed point
and is proportional to its distance from the fixed point.
The motion of a point whose displacement x changes
with time t according to x = A sin (ω t + ε), where A, ω
and ε are constants.
Amplitude, A of an oscillating object
The maximum value of the object’s displacement (from
its equilibrium position).
Phase of an oscillation
The phase of an oscillation is the angle (ωt + ε) in the
equation x = A sin (ω t + ε). [ε is called the phase
constant.]
Free oscillations
[Natural oscillations]
Free oscillations occur when an oscillatory system
(such as a mass on a spring, or a pendulum) is
displaced and released.
[The frequency of the free oscillations is called the
system’s natural frequency.]
Damping
Damping is the dying away, due to resistive forces, of
the amplitude of free oscillations
Critical damping
Critical damping is the case when the resistive forces
on the system are just large enough to prevent
oscillations occurring at all when the system is
displaced and released.
Forced oscillations
These occur when a sinusoidally varying ‘driving’ force
is applied to an oscillatory system, causing it to
oscillate with the frequency of the applied force
Resonance
If, in forced vibrations, the frequency of the applied
force is equal to the natural frequency of the system
(e.g. mass on spring), the amplitude of the resulting
oscillations is large. This is resonance
Ideal gas
An ideal gas strictly obeys the equation of state
pV = nRT, in which n is the number of moles, T is the
kelvin temperature and R is the molar gas constant.
R = 8.31 J mol-1 K-1
. With the exception of very high
densities a real gas approximates well to an ideal gas.
The mole
The mole is the S.I. unit of an ‘amount of substance’. It
is the amount containing as many particles (e.g.
molecules) as there are atoms in 12 g of carbon-12.
Avogadro constant, NA
This is the number of particles per mole.
Internal energy, U, of
a system
This is the sum of the kinetic and potential energies of
the particles of a system
Heat, Q
This is energy flow from a region at higher temperature
to a region at lower temperature, due to the
temperature difference. In thermodynamics we deal
with heat going into or out of a system. It makes no
sense to speak of heat in a system
Work, W
If the system is a gas, in a cylinder fitted with a piston,
the gas does work of amount p x (change in) V when it exerts a pressure p and pushes the piston out a small way, so the gas volume increases by (change in) V. Work, like heat, is energy in transit from (or to) the system
First law of thermodynamics
The increase, (change in) U, in internal energy of a system is (change in) U = Q – W in which Q is the heat entering the system and W is the work done by the system. Any of the terms in the equation can be positive or negative, e.g. if 100 J of heat is lost from a system Q = –100 J.
Define temperature
A measure of the average kinetic energy of particles in a system
