1. 001
Introduction to Thermodynamics
Thermodynamics
The science that deals with the conversion of energy from one form to another, the direction
of the flow of heat, and the availability of energy to do work.
SYSTEM OF UNITS
In the study of thermodynamics, it is important to familiarize ourselves with the fundamental
units that are commonly used to measure physical quantities of thermodynamic substances. Some of
these units are given in Table 1-1.
English
Quantity measured SI Unit
Unit
Length m ft
mass kg lb m
Time s sec
O
Temperature
o
C, K F, o R
Area m2 ft 2
Volume m3 ft 3
m ft
Velocity
s sec
m ft
Acceleration
s2 sec 2
Force N lb f
Energy N-m or J Btu
N
Pressure or Pa
m2 psi
J Btu
Power or W hp,
s sec
NEWTON’S SECOND LAW OF MOTION
Newton’s second law of motion states that the object will accelerate in the direction and
directly proportional to the unbalanced force acting on it.
F α ao
a 
F = m o
g


 C 
Where: F = unbalance force
m = mass of the object
ao = go = observed acceleration or local
gravitational acceleration
m ft
go = 9.81 2 = 32.2
s sec2
gC = proportionality constant
kg − m lbm − ft
gC = 1 = 32.2
N − s2 lbf − sec2

2. PROBLEM SET:
1.1 The weight of the object measured in the Mars is 10 N where the observed gravitational
acceleration is 3.40 m/s2. Determine the weight of the object in earth where the gravitational
acceleration is 9.81 m/s2.
(28.85 N)
1.2 A force of 6 lbs acts on an object with a weight of 35 lbs on earth. Determine the objects
acceleration.
(Ans. 5.52 ft/sec2)
1.3 A spring is compressed by 0.05 in for every 1 lbf of applied force. Determine the deflection of
the same spring when the applied forces is 6.5 lbm. Let go =32.0 ft/sec2.
(Ans. 0.3230 in)
1.4 Determine the force required to accelerate a mass of 25 lbm at a rate of 80 ft/sec2 vertically
upward.
(Ans. 62.11 lbf)
1.5 An upward force is applied to a 5 kg object. The only other force acting on the object is the
force exerted by gravity. If the upward net acceleration of the object is 10 m/s2, determine
the magnitude of the upward force.
(Ans. 99 N)