. Railroad construction. Theory and practice . J. (To lace page 390.) § 350. TRAIN RESISTANCE. 891 allowance for an increase or decrease of kinetic or potentialenergy must therefore be made before it is possible to knowhow much force is being spent on the ordinary resistances. 350. Gravity or drop ** tests. Dynamometer tests requirethe use of a d3namometer which is capable of measuring aforce of several thousands of pounds, and which thereforecannot determine such values with a close percentage of accu-racy, especially if the force is small. A drop test utihzes theforce of gra^dty^ w^hich may
. Railroad construction. Theory and practice . J. (To lace page 390.) § 350. TRAIN RESISTANCE. 891 allowance for an increase or decrease of kinetic or potentialenergy must therefore be made before it is possible to knowhow much force is being spent on the ordinary resistances. 350. Gravity or drop ** tests. Dynamometer tests requirethe use of a d3namometer which is capable of measuring aforce of several thousands of pounds, and which thereforecannot determine such values with a close percentage of accu-racy, especially if the force is small. A drop test utihzes theforce of gra^dty^ w^hich may be measured with, mathematicalaccuracy. The general method is to select a stretch of trackwhich has a uniform grade of about and which is prefer-ably straight for two or three miles. On such a grade carswith running gear in good condition may be started by a velocity will gradually increase until at some velocit}^depending on the resistances encountered, the cars w^ill moveuniformly. The only work recjuiring extreme care with this
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