## Mechanical Comprehension Flash Card Set 121168

 Cards 10 Topics First-Class Lever, Force of Friction, Joules, Mass, Mechanics, Modulus of Elasticity, Normal Force, Specific Gravity, Structural Loads, Tension

#### Study Guide

###### First-Class Lever

A first-class lever is used to increase force or distance while changing the direction of the force. The lever pivots on a fulcrum and, when a force is applied to the lever at one side of the fulcrum, the other end moves in the opposite direction. The position of the fulcrum also defines the mechanical advantage of the lever. If the fulcrum is closer to the force being applied, the load can be moved a greater distance at the expense of requiring a greater input force. If the fulcrum is closer to the load, less force is required but the force must be applied over a longer distance. An example of a first-class lever is a seesaw / teeter-totter.

###### Force of Friction

The formula for force of friction (Ff) is the same whether kinetic or static friction applies: Ff = μFN. To distinguish between kinetic and static friction, μk and μs are often used in place of μ.

###### Joules

The Joule (J) is the standard unit of energy and has the unit $${kg \times m^2} \over s^2$$.

###### Mass

Mass is a measure of the amount of matter in an object. In general, larger objects have larger mass than smaller objects but mass ultimately depends on how compact (dense) a substance is.

###### Mechanics

Mechanics deals with motion and the forces that produce motion.

###### Modulus of Elasticity

The modulus of elasticity measures how much a material or structure will deflect under stress. Stretch modulus is longitudinal stretch (like stretching raw bread dough), shear modulus is longitudinal deflection (like the horizontal displacement of a stack of magzines when a heavy object is placed upon them), and bulk modulus is compression of volume (like the compression of a loaf of bread under a heavy can at the bottom of a grocery bag).

###### Normal Force

Normal force (FN) represents the force a surface exerts when an object presses against it.

###### Specific Gravity

Specific gravity is the ratio of the density of equal volumes of a substance and water and is measured by a hyrdometer.