CHAPTER 2a
ENERGY TRANSFER BY HEAT, WORK & MASS

CONTENTS
Forms of Energy Energy Transfer by Heat Energy Transfer by Work Mechanical Forms of Work The First Law of Thermodynamics Energy Balance for close system Energy Conversion Efficiencies

FORMS OF ENERGY
• Energy can exist in numerous forms such as thermal, mechanical, kinetic, potential, electric, magnetic, chemical, and nuclear, and their sum constitutes the total energy, E of a system. Thermodynamics deals only with the change of the total energy. Macroscopic forms of energy: Those a system possesses as a whole with respect to some outside reference frame, such as kinetic and potential energies. Microscopic forms of energy: Those related to the molecular structure of a system and the degree of the molecular activity. Internal energy, U: The sum of all the microscopic forms of energy. Kinetic energy, KE: The energy that a system possesses as a result of its motion relative to some reference frame. Potential energy, PE: The energy that a system possesses as a result of its elevation in a gravitational field.
The macroscopic energy of an object changes with velocity and elevation.

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ENERGY EQUESIONS
Kinetic energy

Kinetic energy per unit mass
Potential energy Most of the closed system remains stationary, so for that system; KE = PE = 0

Potential energy per unit mass
Total energy of a system Energy of a system per unit mass Total energy per unit mass

PROBLEM
Determined the mass and weight of air contained in a room whose dimensions are 6mx6mx8m assume density of air is 1.16 kg/m3

PROBLEM
Determine the power refined for a 1150 Kg car to climb a 100m long uphill road with a slope of 30° (from horizontal) in a 12 sec ⅰ) at constant velocity ⅱ) from rest to a final velocity of 30 m/s and ⅲ) from 35 m/s to final velocity of 5 m/sec. Disregarding friction, air drag and