pounds on earth weighs 32 pounds on the moon

time. Negative acceleration is commonly called

because of the difference in the pull of gravity.

deceleration.

Yet the mass of the person is exactly the same.

A mathematical formula for mass is as follows:

Mass is equal to the weight of the object divided

by the acceleration due to gravity, or

slug is mass with force and acceleration (due to

gravity) taken into consideration. So, a 1-pound

slug is the mass accelerated by 32 feet per second

per second (32 ft/sec2) when acted upon by a force

of 1 pound.

per second (or feet per second squared).

This means that a free-falling 1-pound object

accelerates at 32.2 feet per second each second that

gravity acts on it. We use the lower case *g *to

express the acceleration due to gravity.

through a distance (work = force x distance). For

example, if you raise a 100-pound weight 10 feet,

Standard day shows conditions at sea level:

1,000 foot pounds of work was done. The amount

barometric pressure--29.92 inches of mercury

of work is the same, regardless of how much time

(Hg); temperature--59.0F.

(rate) is involved.

All gas turbine engines are rated with air at

the standard temperature of 59F. Operation of

engines at a temperature above or below this

temperature will proportionally affect thrust out-

put by as much as 15 or 20 percent. As the

temperature of a slug of air increases, the

In the above example, if the work was done

molecules move faster. They run into each other

with more impact, and move further apart. This

in 10 seconds, power expended was 100 foot

decreases the density of the air. With the decrease

pounds per second. If it took 5 minutes (300

in density, the weight of the air is less, and the

seconds), the rate of power is 3.3 foot pounds per

thrust produced is proportional to the weight of

second. We often talk of power in terms of

the slug of air.

resulting in more molecules per cubic foot, which,

mechanical power and is 33,000 foot pounds per

in turn, increases the weight of the slug of air.

minute, or 550 foot pounds per second. (Foot

The weight of the air affects thrust output.

pound is the energy required to lift a 1-pound

weight 1 foot in height.)

arriving at the engine intake than the engine can

ingest. Ram recovery is the airspeed at which ram

pressure rise is equal to friction pressure loss. This

per unit of time. Expressed in terms like *miles per*

speed varies with duct design factors. Mach 0.2,

or 150 miles per hour, is a representative reference

number for the beginning of ram effect.

Now let's apply the terms we learned to the

principles of thrust.

symbol *V *represents the term *velocity.*

Newton's first law states "A body (mass) at

This definition is not based on distance traveled.

rest tends to remain at rest, and a body in motion

Acceleration is the gain or loss of velocity with