## ASVAB Mechanical Comprehension Practice Test 933458

 Questions 5 Topics Efficiency, Gear Trains, Mechanical Advantage, Second-Class Lever, Universal Gravitation

#### Study Guide

###### Efficiency

The efficiency of a machine describes how much of the power put into the machine is turned into movement or force. A 100% efficient machine would turn all of the input power into output movement or force. However, no machine is 100% efficient due to friction, heat, wear and other imperfections that consume input power without delivering any output.

###### Gear Trains

Connected gears of different numbers of teeth are used together to change the rotational speed and torque of the input force. If the smaller gear drives the larger gear, the speed of rotation will be reduced and the torque will increase. If the larger gear drives the smaller gear, the speed of rotation will increase and the torque will be reduced.

Newton's Law of Univeral Gravitation defines the general formula for the attraction of gravity between two objects: $$\vec{F_{g}} = { Gm_{1}m_{2} \over r^2}$$ . In the specific case of an object falling toward Earth, the acceleration due to gravity (g) is approximately 9.8 m/s2.