= 
FRICTION 
preffion ; and when ‘a lefs ee and — weights were 
I s 
. Similar re. 
ufed, the friction was 
2.40 
fults were obtained in all Cobar s ene even when 
metallic furfaces w loyed. The d 
propolition has alfo been eltabt ifhed by Coulomb. 
that the greateft fri€tion is engendered when oak moves Geen 
I 
pine, and that it amounts to ——- of the force-of preflion ; 
I 
8 
on the contrary, when iron ao upon brafs, the leaft fric- 
tion is produced, and it amounts to 4 of the force of pref- 
fion. 
riGtion is in general not increafed by augmenting the 
aac Mufehenbroek and Nollet entertained the 
The aa of Krafft coincide with 
= Coulomb. See Com ela Peas Sanne: 
p- 266, § 19, Whe a fuperticies 
thr ee feet {quare was employed, the friGtion, “with different 
at a medium; but when a {maller 
hts as : 
wei Ww. 
uae 2.28 
furface was ufed, the friCtion, inftead’ of being greater, as 
might havebech expeGed, was only = 
6. Friction - the moft - is not agent ted by an 
ereafe of veloc In fome cafes, however, it is dininifhed 
by an aremeral of ecleritye ML Colas found, that 
when wood moved upon eee in the a of the fibres, 
the friction was a conftant q ek however much the velo- 
city was-varied ; but that wen the unaces we were very {mall 
e ed, ¢ 
in refpect to the force wit the fric- 
tion was diminifbed by augmenting the rapidity + ae friction, 
on the contrary, was increafed when the furfaces were very 
a 
“3 
6 
_ 
an 
< 
friGtion in an cafe rem: mo 
tals, the . Bion is ‘gently er ies an ae 
metals move upon wood befme 
with tallow, the fietion | is ftill arena by adding to the 
velocity. When metals ~~ upon metals, the friction is 
but when heterogeneous fu 
be Spee wi ne tallow, 
the velocity, o for 
arithmetical progreffion when the velocities aa a ieee 
ca ona 
£ 
~ 
_ 4. The. friction of loaded cylinders rolling upon a_hori- 
zon cial plane is in the direct ratio of their w platen th 
inverfe ratio of their diameters. In Coulomb’s experiments, 
. the friction, of ails rs, of guaiacum wood, which were two 
inches in diam eter, and were loaded with 1000 pounds, was 
18 pounds. or sig of the force of prefiion. In cylinders of 
elm, the friétion was greater by 2, and was {carcely dimi- 
nifhed by: the ciepoaten of tallow 
From a variety of experiments on the friGlio 
of pullies, Coulomb obtained the sas. ere -When 
an iron axle moved in a bra. th or bed, the fri€ was 4 
f the preffion; but when the uth was Selineared with 
very clean tallow, the fri€tion was only, 5 ee fwine’s 
F = and 
when olive oil was employed as an unguent, the friction was 
greafe was interpofed, the friétion amounted to 
I 
never lefs than 4 or—. ‘When the axis was of ‘green 
eak, and the bush of guaiacum wood, the friction was 3. 
when tallow was interpofed; but when the tallow ‘was re- 
moved fo that a {mall quantity of greafe oy covered the 
VoL. XV. 
on of the aKes’ is not produced till after the lapfe of ee Se 
‘the furface of preffur 
furface, the friction. was inereafed to ,‘,.. When th; 
m, the fridion was in Eitan circumitances 
f preflion 
Mr. ion Leflie 
Tor the caer of Edinbur 
(See his | Ge work on the nature and pro pagation oF 
heat, chap. xv. p. 299, &c.) “If the two furfaces,”’ fays 
this ingenious writer, ‘which rub againit for aed are 
rough and uneven, ats is - cane wa "Ce, OC~ 
the grinding ralion of a prominence, 
But friGion fabiilts he) te noe furfaces are w 
down as regular and fmooth as poffible. In fa&t, the 
elaborate polifh can operate no other chan 
the fize of the natural _afperities. 
being moulded 
ci 
te the boundary 
otal ‘elevations 
will be equalled by 
n the general m 
«A dhefion feeme {till leis aoe of accounting for the 
in of fri€tio erpendicular force acting on a folid 
can oT ety hae no Effect to impede its progrefs; and 
though this lateral force, owing to the unavoidable inequa 
lities of contact fubject toa certain irregular obli- 
i the hole 
e€ ceo ee furfaces oe efore, 6 remain ybe 
Jutely paffive, no aber could. eve ee ts exiftence 
emonitrates er mutual c ange of figure, - the 
oppotite nines, aur ing the pafla eee con eee ee to 
accommodate themfelves to all oo 
rieties of contact. - 
T his adaptation 
requires very 
olla periods to attain its ili according to the na- 
ure and relation of the fubftances concerned. In fom 
feconds are faficient, | in ei. the full fic 
While 
the incumbent mafs is drawn along, at every itage of its ad- 
vance, it changes its external configuration, and approaches 
more or lefs towards a Hone ey wi Be aa ee fur- 
fa e effort required to put motion, 
nee meafure of fridtion, ae if 
nge attends generally an 
mented rapidity,, ‘This appears saat) oe by the 
curious experiments of Sanne the mo rinal and va- 
luable which have been ‘ma that eae fubjec. 
FriGtion confifts in = force expende to raife continually 
e by an oblique a¢tion. ° The upper 
furface wavels over a perpetual fyftem of inclined Planes ; 3 
3A but 
on a few 
