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# Mechanical Comprehension Study Guide 2 for McGraw-Hill's ASVAB (page 6)

By Dr. Janet E. Wall
McGraw-Hill Professional
Updated on Jun 26, 2011

### Glossary

• chemical energy. Energy stored in chemicals or released in a chemical reaction
• compression. A force that pushes materials together
• compound machine. A machine made up of two or more simple machines working together
• effort. In a lever, the point where you apply force
• effort arm. In a lever, the distance from the force to the fulcrum
• electrical energy. Energy in moving electrons
• flexibility. The ability of a material to bend without breaking
• friction. The force that resists the relative motion of two surfaces in contact
• fulcrum. The stationary element that holds a lever but also allows it to rotate
• gravity. An attractive force between objects
• kinetic energy. Energy in a moving object
• load. In a lever, the part where output force lifts or squeezes
• load arm. In a lever, the distance from the load to the fulcrum
• mechanical advantage. The amount by which a machine multiplies the force applied to it
• potential energy. Energy that can be released under certain conditions
• tension. A force that pulls materials apart

### Laws and Formulas to Know

How to calculate mechanical advantage (MA):

• Lever: MA = load/effort = effort distance/load distance
• Pulley: MA = load/effort = number of supporting Strands
• Gears: MA = number of teeth on driven gear/ number of teeth on driving gear
• Sheaves: MA = driven diameter/drive diameter
• Inclined plane: MA = horizontal length/vertical rise
• Wheel and axle: MA = radius of wheel/radius of axle

Speed of pulleys in a system:

Speed1 × diameter1 = speed2 × diameter2

The gas laws:

• When a gas is compressed, it heats up.
• When a given amount of gas expands, its pressure drops and the gas cools.
• When a gas cools without a change in outside pressure, it loses volume.

Water pressure:

• Total flow through a pipe system is the same everywhere.
• When liquid speeds up, pressure falls.
• When liquid slows down, pressure rises.

Practice problems for this study guide can be found at:

Mechanical Comprehension Practice Problems for McGraw-Hill's ASVAB

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