UCSD DEPARTMENT OF PHYSICS Winter Quarter 2000

PHYSICS 8: THE PHYSICS OF EVERYDAY LIFE

Homework 3 Solutions 1. Sketch a gear arrangement that will change the speed of rotation by a factor of three, and will move the axis of rotation by 90 degrees. *********************************************************************** Text Reference p 37 - Beveled gears will do the axis rotation, and for the speed rate change one must have the ratio of gear diameters (and hence circumferences) as 3. For example, 6 and 2, 30 and 10, etc... Note the teeth spacing must be the same on both gears. ************************************************************************** ************************************************************************** 2. Sketch a device which could lift a car off the ground. ************************************************************ A few ways to do this. Various combinations of gears, pulleys, levers possible. A hydraulic method (as in most car garages) is superior though. **************************************************************************** **************************************************************************** 3. Explain how a gyroscope works. ************************************** Text Reference p 76-7 - As with others, must be in own words which display an understanding of presented material. Make sure you understand its key principles -- likes to maintain axis pointing in same direction, and the wanderign of the axis called precession. **************************************************************************** **************************************************************************** 4. How is a spring used to measure weight? ************************************************ Text Reference p 24-5, p.78 The change in the length of the spring is prportional (varies as) the force applied. The force is that of gravity pulling down on the object which you are weighing. See above guideline. *************************************************************************** *************************************************************************** 5. Name 4 devices which rely on friction. ******************************************** Many to choose from. For example: brakes, car tires, matchbox/lighter, parachute. Note the question asks for "devices" and not "materials", like velcro (uses hooks rather than friction) and surfboard wax may not be fully acceptable. ***********************************************************************

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