Although the third order of lever is particularly inefficient when the fulcrum is rigid and immobile, it possesses singular advantages when these conditions are reversed, that is, when the fulcrum, as happens with the air, is elastic and yielding.
The line j oining the end knife edges must be exactly bisected by a line drawn perpendicular to it from the fulcrum knife-edge.
The balloon has no hold upon the air, and this consequently cannot be employed as a fulcrum for regulating its course.
When the wing ascends as shown at p, the air (fulcrum f) resists its upward passage, and forces the body (b) or its representative (w) slightly downwards.
When the wing descends as shown at p', the air (fulcrum f) resists its downward passage, and forces the body (b) or its representative (w') slightly upwards.
The theory of the scale-beam is stated by Weisbach in his Mechanics of Machinery and Engineering, as follows - In fig I D is the fulcrum of the balance, S the centre of gravity of the beam alone without the scales, chains or weights; A and B the points of suspension of the chains.
The pair of beams are hung centrally by rods and hooks from knife-edges in the forked end of a strong beam, which is carried at its fulcrum by the top plate of the frame of the machine.
4) a point in the steady mass b is used as the fulcrum for the short arm of a light-writing index.
They are constructed with the fulcrum knife-edges lower than the line joining the end knife-edges, and they are arranged so that the beam is horizontal when the stop of the weights-pan is hard down on its bearings.
For the latter purpose machines are used of which the beams are made stable, or " vibrating," by constructing them with the fulcrum knife-edges above the line joining the end knife-edges.
This upper steelyard is arranged as in fig 9, where A is the point where the pull of the long body lever due to the weight of the goods on the platform comes upon the steelyard; C is the fulcrum of the steelyard, which with the steelyard can be slid to and fro on the frame of the machine; and Q 8 s frl FIG.
The power is represented by the wing, the fulcrum by the air, and the weight by the body of the flying animal.
If W be the weight in each pan when the goods-pan commenced to sink, / the length of each arm, m the distance of the fulcrum below the line joining the end knife-edges, and 13 the angle at the fulcrum which defines the range of sway of the beam, it can easily be shown that w, the ad - ditional weight required in the weights-pan to enable the goods-pan to rise from its stop, is given by the equation w =W 2m tan, 3/L m tan S.
With the smallest excess of moment on the left-hand side of the fulcrum, the end C of the steelyard will rise with accelerating velocity till it is brought up by a stop of some sort; and with the smallest excess of moment on the right-hand side of the fulcrum, the end C of the steelyard will drop, and will descend with accelerating velocity till it is brought up by a similar stop. If Z be above the line XH, the steelyard is " vibrating "; i.e.
A, malleate, with crop: this is followed enlarged view of malleus above - the by the crop-gizzard, Y-shaped incus consists of a short median also ciliated except fulcrum bearing two large rami, each of behind, where it is which is in contact with a stout malleus hardened into a set consisting of a toothed uncus carried on a of articulated sclerites long manubrium; b, sub-malleate, with (trophi) to form the enlarged view of malleus - the manubria gizzard or mastax.
This is the principle of the modification of motion by the lever, which consists of a rigid body turning about a fixed axis called a fulcrum, and having two points at the same or different distances from that axis, and in the same or different directions, one of which receives motion and the other transmits motion, modified in direction and velocity according to the above law.