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.

## HFC1 Reactions of Beams Apparatus

This apparatus is designed for simple experiments and demonstrations on simply supported beams. Two spring balances act as supports and enable reactions to be read directly. Three movable load hangers allow loads to be put in a number of positions.

## HFC2 Triangle of Forces Apparatus

A bench mounted circular table with a central pin and 360º protractor has three pulleys on adjustable clamps round the edge. Conditions of equilibrium are obtained by centralising a small cord ring over the central pin with cords to load hangers where the loads and lines of action are variable. The triangle of forces in equilibrium can be constructed and the resultant of two known forces can be found.

## HFC3 Funicular Polygon and Forces Apparatus

This apparatus is a more comprehensive and versatile version of the HFC2. A simple but elegant demonstration of the conditions of equilibrium for three or more coplanar forces acting either at a point, on a circular disc or on a rectangular shape.

## HFC4 Shearing Force Apparatus

This experiment demonstrates the nature of the internal forces and their dependence on the external system of forces for a simply supported beam. The experimental beam is in two parts, joined by a pair of ball bearing rollers running in flat vertical tracks. To develop the internal beam forces at the section an underslung tension spring is used to resist the bending moment, while an overhung spring balance provides the vertical shearing force. The shear force can then be directly read from the vertical spring balance. The beam is simply supported on end bearings and several weight hangers can be attached at any position on either side of the joint.

## HFC5 Bending Moment Apparatus

This experiment demonstrates the nature of internal forces and their dependence on the external system of forces for a simply supported beam. The experimental beam is in two parts joined by a pair of ball bearings running in a profiled groove. An underslung spring balance provides a resisting moment, and also allows the section bending moment to be measured. When load is applied to the beams the spring balance is adjusted to bring the beam horizontal and the bending moment force recorded. Load is applied by the use of calibrated weights and three specially designed hangers which have a single point contact on the beam and can be positioned anywhere along the working length of the beam section. The beam is simply supported on end bearings. The apparatus is quick and easy to set-up on a bench top and takes up little space. It is a visual experiment and different loadings can be applied accurately and quickly.

## 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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