Physics of Machines and Projectile Motion: Work, Power, and Efficiency, Study notes of Physics

Download Physics of Machines and Projectile Motion: Work, Power, and Efficiency and more Study notes Physics in PDF only on Docsity! 10/2/2008 1 Machines and Projectile Motion Mechanic’s Magazine, Vol. II. (Knight and Lacey, London, 1824) Momentum, Impulse, Energy, Work, Power vmp   pvmtF tot   Momentum: Impulse: Energy: Kinetic energy, gravitational potential energy, etc. Work: shows how forces affect energy via the Work-Energy Theorem Power: A measure of how fast work is done Work and Power • Power, P, is a measure of how fast work is done, or • A worker uses more power running up the stairs than climbing the same stairs slowly. • Unit of power is the Watt: 1 Watt= 1 Joule/sec. . t W P done   Power and Lance Armstrong Stage 13 of the Tour de France ends in a 820 m climb over 12.5 km. Lance Armstrong did it in about 20 minutes with a road speed of about 25 mph. What is Lance’s power output? Power and Niagara Falls Machines Machines multiply forces or change the direction of the force Machines cannot create energy but can transform energy from one form to another Machines cannot multiply work, in fact, for ideal machines, work input = work output. 10/2/2008 2 Levers Pulleys Machines and Efficiency In reality, when operating a machine, some energy is dissipated to thermal energy, which makes the machine and the surroundings warmer. Efficiency characterizes this loss with inputenergyTotal outputenergyUseful Efficiency  Efficiency Now let’s come back full circle to momentum • Kinetic energy is conserved in elastic collisions---Newton’s Cradle • Kinetic energy is NOT conserved in inelastic collision----KE withdrawn to deform objects involved in the collision Collision Problem • Place a small ball a short distance above a large ball. Drop both at the same time with the large ball at a height of 1.8 m. Describe what happens under the assumption that ball- ball and ball-ground collisions are elastic.