Air Track Rail Air Track Rail, Basic Equipment

Transcription

1 R Air Track Rail Air Track Rail, Basic Equipment Operating Instructions 1 PURPOSE AND CHARACTERISTICS With its extremely low friction the set of equipment, Air Track Rail , is ideally suitable for investigating kinematic and dynamic behaviour in straight line motion. The main component in this system of equipment is the 2m long Air Track Rail on which numerous experiments can be carried out with the aid of the separate parts included with The relationship between displacement, time, velocity and acceleration as well as the dynamic coupling of these quantities can be determined in impressive experiments. Supplementary electronic measurement equipment (light barriers, electronic timers, computer-aided measurement acquisition systems) are needed for the time measurement. 2 DESCRIPTION The Air Track Rail Basic Equipment consists of the following individual parts. 1 Air Track Rail The track is formed by a 2m long aluminium tube with a square cross-sectional shape (63mm 3 63mm). The track is terminated at the end of the tube; the end face at the start of the track has an opening (d = 40mm) for connecting a Blower via the Pressure Tube The two gliding surfaces each have two rows of holes which are displaced with respect to one another; hole diameter 1mm, separation 20mm. An air cushion is formed under the gliders which are positioned on the track by the emitted compressed air, so that the gliders can glide along the track with almost no friction. For the measurement of the length the two gliding surfaces have two scales running in opposite directions with mm divisions and cm figures. Two knurled screws are fitted at the ends of the track, enabling the track to be fitted to the end-holders included with ; they should be used in this position provided the experimental objective does not require a different arrangement. The square tube rests on a U-section carrier rail which is supported on the experiment bench with its feet in a three-point arrangement; two adjustment screws provide the horizontal alignment of the track. The square pipe and carrier rail are joined with seven screws which have been used to adjust the track as supplied exworks (basic adjustment). Since the screws on the bottom of the rail are accessible, a track which has been thrown out of adjustment by improper handling can be readjusted by the user, see 3.4. However, unless there is a compelling reason, the screws should not be altered. 2 End-Holder for Air Track Rail (two included) These are attached to the air track rail at the ends of the track using the appropriate knurled screws. Note: If the mechanical starting system is used, consisting of items and (not included in ), then the starting system is fastened to the air track rail instead of an end-holder. 3 Glider (two included) Roof-shaped, 130mm long, black anodised aluminium profile section for placing on the track. A ridge strip with five 4mm sockets enables screens and other plug-in elements to be fitted. The mass of the glider itself is approximately 170g; with fitted screen, l = 100mm and two plug-in elements the mass increases to a total of about 200g. Scales are PHYWE SYSTEME GMBH Robert-Bosch-Breite 10 D Göttingen Telefon (05 51) Telefax (05 51)

2 INITIAL OPERATION AND HANDLING 3.1 General remarks Before the air track rail is operated, an End-Holder should be fastened to the end of the track with the two knurled screws. Normally, an end-holder is also attaneeded to find the exact weight. To increase the mass to 300g or 400g, 50g Slotted Weights ( ) can be placed on the two steel pins and evenly distributed on both sides for reasons of symmetry. Also for this reason, both end faces should always be fitted with a plugin element even when only one is needed. 4 Screen Screen (two of each included) The black plastic screens are plugged onto the ridge strip of the glider with their 4mm plugs. They are used to control timing instruments (e.g. Electronic Digital Counter, 6 decade ( ), 4 decade ( )) through light barriers fitted to the track. The two 50mm high screens differ in their length and mass: Screen Length Mass mm ± 0.2mm 10g ± 1g mm ± 0.1mm 5g ± 0.5g Plug-in elements The plug-in elements listed below (with 4mm plug) all have the same mass (10 g ±1 g) and the same position for the centre of gravity, so that the glider is symmetrically loaded when both end faces are fitted with a plugin element. With four pairs of grooves for clamping a rubber band from The rubber band must not sag, but should not be under strong tension. The fork with rubber band is used for the elastic collision. Two gliders are fitted on facing ends with the fork or the Plate with Plug It is recommended that the plug-in elements are fitted to the lower holes in the gliders, because with the elastic collision a small torque affects the gliders and energy losses are thus minimised. 6 Rubber Band (10 pcs) for clamping in the pair of grooves in the fork Plate with Plug For plugging (with vertical plate) on the end face of the glider. The plate forms the opposing element to the Fork during the elastic collision. 8 Tube with Plug Needle with Plug For an inelastic collision the plug-in elements are plugged onto the two opposing end faces of the gliders (it is recommended that the lower holes are used). During the collision the needle penetrates the plasticine filling of the tube, firmly coupling both gliders together. The plug combination of the tube and needle can also be used to retain a glider at the end holder after its movement has taken place. Please refer to the list of equipment for other parts needed to conduct experiments. 2

3 ched to the start of the track (the end with the pressure tube connection), unless the mechanical starting system ( ) (not included in ) is used. In this case it is fitted instead of the end-holder. The air track rail is set up on a flat surface that is as level as possible and connected to the blower using the pressure tube. The blower pressure should be set such that the gliders just reliably elevate from the track and are freely supported on the air cushion; depending on the glider load this can be at different pressures. A blower pressure that is too high should be avoided, because it impairs the steady positioning of the glider. The track, which itself has been adjusted at the works, must be aligned as level as possible with the two adjustment screws on the base of the carrier rail. This can be initially carried out by eye or using a spirit level; accurate alignment must be obtained with the blower operating and by setting a glider on the track. With a properly levelled track there should be no or very little glider acceleration ; a slight pendulum movement caused by the air current is unavoidable. This test should be conducted on various points on the track. The action of external forces, e.g. due to vibration or draughts should be avoided. 3.2 Electronic timing The electronic digital counters mentioned in the list of equipment are suitable for the time measurement. One or two light barriers can be connected to these devices for electro-optical control. The light barriers must be arranged at the required point on the track so that the screen on the glider interrupts the beam of light between the light source and the photoelectric sensor when it passes. A holder made from stand-support components is suitable. A ruler with gliders can be attached to the holding structure to demonstrate the length measurement. 3.3 Producing constant acceleration The glider should be fitted with the Hook ( *). To produce the acceleration, a Silk Thread ( *) to the end of which a Weight Holder ( *) is attached, is passed over a low-friction Precision Pulley ( *). One or more 1g Slotted Weights ( *) are placed on the holder; up to 20g is permissible for the pulley. Since the nominal mass of the glider (200g for the glider with 100mm screen and two plug-in elements) is subject to a certain tolerance, weighing should be carried out to exactly determine the accelerated mass and supplementary weights used if required. Also, the mass of the weight holder (1g) and the 1g slotted weights used must be taken into account as an additional corrective quantity; an equivalent mass for the rotating pulley can be taken as 2.2g. needed to adjust these M6 screws (pitch 1mm/turn). Generally for readjustment, an adjustment of only up to one half turn of the screw is required which must be taken in stages and the track straightness should be tested at each stage. By turning the screw clockwise the square tube is pulled downwards in the vicinity of the screw and it is raised when the screw is turned in the opposite direction. The longitudinal straightness of the track section should at least be determined qualitatively before the adjusting screws are adjusted. This is done with the blower operating and with the aid of a glider put on the air track rail. First the track should be aligned with it level at the centre. Then the glider is positioned at various points along the track and the direction and approximate magnitude of the acceleration occurring at that point is found. (If an estimate is not regarded as being sufficient, the time t for the glider to move from its starting point over a distance s can be determined. The acceleration is then a = 2 s/t 2 ). The magnitude is a measure of the gradient of the track at the test point. It is essential that external force affects, such as draughts, are avoided during the test. The qualitative straightness of the track can be found from the results and, as an aid, can be drawn out. It may be, for example, that a maximum or a minimum is present in the central track section. Then the adjustment screws are adjusted at the point of the extreme misalignment and the surrounding vicinity according to the determined misalignment. As mentioned above, this should be carried out in small steps. Finally, the straightness of the track should be tested along the whole track. If the misalignment exhibits a number of extreme points, then an analogous procedure should be followed for their correction. 4 EXPERIMENT LITERATURE Versuchseinheiten Physik, Lineare Bewegungen Physik in Demonstrationsversuchen, Ausgabe A/B, Band Mechanik Physik in Demonstrationsversuchen, Ausgabe C, Teil University Practicals in Physics Manual for COMEX Air Track Rail Computer-Aided Measurement Acquisition and Evaluation of Air Track Rail Experiments with the COMEX Interface System * not included in Readjusting the air track rail A feature of the Air Track Rail is that it can be readjusted with regard to the straightness of its longitudinal profile. Correction of the basic ex-works adjustment is however only necessary it the straightness has become impaired due to mechanical stressing of the track. The adjustment procedure demands a certain amount of manual skill as well as a systematic method of working and assuming this, it can be carried out by the user. Seven Allen screws accessible on the bottom of the carrier rail are to be adjusted where required. A normal Allen key, 5mm AF, is 3

4 5 LIST OF EQUIPMENT 5.1 Items supplied in Air Track Rail 2 End-Holder (23) Glider (23) Screen, l = 100mm (23) Screen, l = 25mm (23) Rubber Band, 10 pcs Plate with Plug Tube with Plug Needle with Plug Other parts required (not included in ) 10 Blower Pressure Tube, l = 1.5m with end connections Precision Pulley Weight Holder lotted Weight 1g, natural colour (53) Slotted Weight 50g, black (83) Silk Thread, l = 200m Hook with Plug Starting System, mechanical, with trigger Magnet with Plug Jet Glider Stop, adjustable (as alternative to End-Holder 2) (23) Air Damping As alternative to the mechanical starting system 18, 19: Starting system, electromagnetic, consisting of: 23 Coil 400 turns Iron Core Holder with Plug Rubber Band, 1 pc. from Silicon Diode 1N with no illustration: Light Barrier (23) Electronic Digital Counter 4 Decade Decade (Both counters supply the 5V voltage required for operating the light barriers.) Plasticine Wall Bracket for Air Track Rail Dust Cover for Air Track Rail

5 The air track rail used with the COMEX System including the tracking plug-in unit and the light barrier rail. Computer-Aided Measurement Acquisition and Evaluation of Air Track Rail Experiments with the COMEX System Material COMEX Basic Unit for housing and supply of COMEX plug-in units. IEEE-488 Bus Interface for IBM-PC and compatible computers IEEE-488 Connecting Cable The COMEX System with the Tracking Plug-in Unit ( ), the Light-Barrier Rail ( ) and the Air Track Rail Program ( ) gives the possibility of conducting, evaluating and impressively demonstrating numerous new experiments with the air track rail and also experiments that have already been well proven in education. The positions and velocities of the gliders are measured with a time resolution of 5 millionths of a second and passed to the computer. Already after only one run up to 80 items of data about time, position and velocity are available which can be displayed numerically or graphically. Through simultaneous tracking of two, completely independent gliders in any direction of movement, the laws of collision and the conservation of momentum can be experimentally investigated in an easy and methodically clear manner. The measurements can be immediately checked with respect to their physical relationships in special display windows in the program. Technical data Memory capacity up to 5 screen passes per single light barrier with absolute time and shading duration. Time resolution 1/187.5kHz for shading duration 1/5.558kHz for absolute time Duration of experiment maximum 11s Connection of light-barrier rail via 14-pole socket IEC device address 6 Housing plug-in cassette 19, 3 ht. divs. COMEX Tracking Plug-in Unit Light-Barrier Rail for measuring the motion sequences on the air track rail; 8 light barriers at intervals of 200mm; 14-pole socket for connection of the tracking plug-in unit; 2 adjustable support bars for holding the rail in various positions; dimensions: (cm). The following are contained in : Connecting lead for the light-barrier rail. Precision Screens, Set of cf. Item 27, page 2 Program for tracking plug-in unit: Diskette, Air Track Rail for measurement acquisition and evaluation of experiments with 1 or 2 gliders, e.g. elastic/inelastic collisions, laws of conservation of energy/momentum, tabular and graphical evaluation... The program runs on all IBM-PC and compatible computers and automatically supports CGA, EGA, VGA and HGC graphics cards. All graphs and tables can be output with comments via Epson compatible matrix printers. With collision experiments the measurement points are displayed with different symbols (before and after the collision) and when using two gliders the motion curves are displayed in different colours. Therefore, it can be easily seen which glider has produced each point and which direction it was moving at that point in time. 5