PC1431 Lectures 30 - 31
Second Law of Thermodynamics:
Heat Engines
Need for 2nd Law of Thermodynamics
Many processes (thermal or otherwise) satisfy the first law
(conservation of energy) but never occur, e.g,
Helium from a punctured balloon spread around
FirstLawof
Thermodynamics
PC1431 Lectures 28 - 29
Heat Q
System
Change in
Internal
energy U
Work W
Surroundings
ThermodynamicProcesses&
Variables
Quasi-static process: Processes that are carried out slowly
enough so that the system passes through a conti
Engineering Physics
List of Questions 1
Note: Some of these questions will be discussed in class, but not all. Questions which are not
discussed in class are considered optional. For tutorial 1, questions 1 to 5 will be discussed.
The questions to be disc
PC1431 Lecture 32 - 33
Second Law of Thermodynamics:
Entropy
Entropy
So far we have seen some aspects of 2nd Law, but have not
made any general statement. More general statement can
be made in terms of entropy, introduced by Clausius in
1860s.
Entropy,
Q1.
From ideal gas state equation PV=nRT:
kh
p1 V hA
p1V p2V2
A
T1
T2
T2
T2
kV
p1V p1V p1 A h kh 2
T1
A
kV
kh 2 p1 A
A
h
kV
p1 A
A
T2
h 1 p1V 0
T1
2
T
kV
p1 A 4k 2 1 p1V
T
A
1
2k
In the limit k 0 (isobaric expansion),
T
T
V
V V hA
p1 Ah
Engineering Physics
Question List 2
Question QL2-1:
A cylinder of cross-sectional area A is closed by a piston that is connected to a spring of
constant k (see Figure P19.50). With the spring relaxed, the cylinder is filled with a volume V
of gas at an in
PC1431 Lecture 28
Kinetic Theory of
Gases
Molecular Model of an Ideal Gas
Assumptions
Large number of molecules; separation > dimension of
molecules. Molecules occupy negligible volume - treated as
point-like.
Obey Newtons laws of motion, but move rando
PC1431Lectures2122
AdditionalSlides&Solutionsto
Problems
Newtons Law of Gravitation
& Planetary Motion
Observation of Planetary movement
Movement of stars and planets
appear differently to an observer on
Earth - retrograde motion of planets.
One way to ex
Oscillations:
Simple Harmonic Motion
Damped & Forced Oscillations
PC1431 Lectures 23 & 24
Examples of Oscillatory Motion
Mass on a spring
Pendulum (e.g., simple, physical, torsion)
Vibrations of a stringed musical instrument
Electromagnetic waves (light,
PC1431Lectures2122
Newtons Law of Gravitation
&
Planetary Motion
Newton, (apple) and Moon
I deduced that the forces that keep the planets in their orbs must be
reciprocally as the squares of their distances from the centres about
which they revolve; and t
Angular
Momentum
PC1431 Lecture 20
Vector (Cross) Product
Given two vectors A and B, the
vector product is another vector C.
The magnitude of C is:
It is equal to the area of
parallelogram formed by
the vectors.
The direction of C is
perpendicular to the
Centre of Mass &
System of particles
PC1431 Lectures 14 15
Centre of Mass
A mechanical system moves as if all its mass were concentrated
at its centre of mass (CM).
If an external force F acts
on this system of
total mass M, the CM
accelerates at a = F/M.
Rotational
Dynamics &
Rolling Motion
PC1431 Lectures 18 19
Definition of Torque
Torque (moment) is a measure of the tendency of a force to rotate
an object about some axis.
The line of action of a force is
an imaginary line extending out
both ends of the
Linear Momentum
& Collisions
PC1431 Lecture 13
Linear Momentum
Linear momentum tells us both something about the object and
something about its motion.
The linear momentum of a particle of mass m moving with velocity
v is defined to be:
Components (rectan
PC1431: Lecture 02
Tooling-Up: Measurements &
Simple Properties of Vectors
Quantities and Units
Experiments require measurements of physical
quantities.
Every measurement give a number (value depends on
units that goes with it.)
SI (metric) vs Imperial (B