The FORCES range enables clear and comprehensive learning of STATICS and DYNAMICS covering a variety of theories and topics. An understanding of the way in which forces act and react, is fundamental when studying the application of loads on a variety of fixed structures and rotating machinery. The FORCES form a comprehensive range of equipment, from fixed beams through to rotating machines apparatus, equally suitable for demonstration and experimental work.

## HFC8 Centre of Gravity Apparatus

The centre of gravity of a shape of uniform thickness can easily be found by this method. It provides a simple technique for complicated shapes, far quicker than by using calculus for example, although not producing an accurate answer to the handling of a yacht, the calculation of the moments caused by the wind and water acting at the 'centre of lateral area' of the sails and keel are still used as a starting point. A free standing backboard has a pin from which a selection of flat shapes can be hung. A simple pendulum suspended from the pin enables the line of action of the weight to be transferred to the lamina. The centre of gravity is the position on the shape where two or more such lines intersect. The shapes can be marked using a suitable pen and can be cleaned easily.

## HFC9 Bell Crank Lever

Lever mechanisms of all shapes and sizes are very common parts of machines, particularly in hand operated devices. The bell crank lever offers the typical mechanical advantage of a lever, and in addition it turns the line of action of the effort through 90°. In most cases the cranked lever would be a casting with a bushed pivot at the corner. The experimental model has been built up from plastic to simulate the real thing.

## HFC12 Three Wire Suspension

A free standing backboard provides supports for three tensile suspenders that meet at a ring carrying a load hanger.

Spring balances measure the tension in each of the suspenders which are at about 30 and 45 degrees to the central vertical one.

## HFC13 Rolling Disc on an Inclined Plane

The moment of inertia of a rolling object is the rotary analogy of mass and governs the rotary acceleration. It can be determined in three ways; by rolling, oscillation or direct calculation. All should ideally give the same result but the student can be introduced to differences caused by different experimental techniques.

## HFC14 Wall Jib Crane

This apparatus teaches students about the confluence of the four forces at the end of the wall jib crane and clearly illustrates the application of a triangle of forces. This wall mounted self-contained jib crane has spring balances built into its two members. After loading the member lengths can be adjusted to their no-load lengths. The experiment allows the student to determine the experimental values of the forces in the principal parts of the jib crane, study the effect of altering the length of the tie to change the geometry and to compare the results with the forces obtained from graphical solutions using a polygon or a triangle of forces. The jib out-hangs and the crane cable inclination can be readily changed. A set of calibrated weights and load hangers are supplied.

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