title: The Mechanical Universe: Introduction to Mechanics and Heat
author:  Richard P. Olenick 
description: This important textbook is based on, though independent of, an educational TV series. Its aim is to guide students and general readers to an understanding of how the physical world works; physics is presented as a human endeavour, with historical development forming a thread throughout the text.
zlib_text: CHAPTER 23 
  HEAT AND TEMPERATURE 
  23.1 HOT AND COLD BODIES 
  When we rub our hands for some time, they 
  become warm. When a block slides on a rough surface, 
  it becomes warm. Press against a rapidly spinning 
  wheel. The wheel slows down and becomes warm. 
  While going on a bicycle, touch the road with your 
  shoe. The bicycle slows down and the shoe becomes 
  warm. When two vehicles collide with each other 
  during an accident, they become very hot. When 
  an aeroplane crashes, it becomes so hot that it 
  catches fire. 
  In each of these examples, mechanical energy is 
  lost and the bodies in question become hot. Where does 
  the mechanical energy vanish ? It goes into the 
  internal energy of the bodies. We conclude that the 
  cold bodies absorb energy to become hot. In other 
  words, a hot body has more internal energy than an 
  otherwise identical cold body. 
  When a hot body is kept in contact with a cold 
  body, the cold body warms up and the hot body cools 
  down. The internal energy of the hot b