Mechanics.

Thf. Celerity or Velocity of Motion is thatAffection by which a Body passes over agiven Space in a given ’Time , or what we

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accelerated, because Gravity every Moment adds a newImpulse, which generates a new Degree of Velocity;and the Velocity thus increasing the Motion must bequicken’d each Moment, or fall faster and faster thelonger it falls.

3. In like Manner, a Body thrown perpendicularlyupward, as a Ball from a Cannon, will have its Motioncontinually retarded, because Gravity acts constantly up-on it in a Direction contrary to that given it by thePowder, so that its Velocity upwards must be continu-ally diminished, and so its Motion is continually retard-ed, t;ll at last it be all destroy’d. The Body has thenattain’d its utmost Height, and is for a Moment mo-tionless, after which it begins to descend with a Velo-city in the same Manner accelerated, till it comes to theEarth’s Surface.

4. And because at a small Distance from the Earth'sSurface, the Power of Gravity is every where the same,it follows, that in equal Moments of Time the Im-pulses on the Body will be equal, which will therefore ge-nerate an equal Increase of Velocity each Moment, andof Consequence the Motion resulting from thence willbe equally quicken’d if downwards, or retarded if up-wards, in Mediums without Resistance.

5. In this Cafe we may observe in Bodies that areprojected upwards, (1.) That the Time of the Ascentis equal to that of the Descent. (2.) That at equalHeights above the Earth, the Velocity in the Ascentand Descent is equal, or the fame ; and therefore, (3.)That the Velocity acquired (by falling) at the Earth’sSurface, is equal to that which is generated by the Pow-der, or other Impetus (which threw it up) in the firstMoment of its Motion. What Difference will arisefrom a resist ng Medium (as to Projectiles thrown up inthe Air, tdc.) will be hereafter more fully consider’d aridspecified.

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