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Gravitational Torsion Balance

AP-8215A

I n s t r u c t i o n M a n u a l w i t h

E x p e r i m e n t G u i d e a n d

T e a c h e r s ’ N o t e s

0 12 - 11 0 3 2 C

*012-11032*

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Summary of Contents for AP-8215A

Page 1: ...tational Torsion Balance AP 8215A Instruction Manual with Experiment Guide and Teachers Notes 012 11032C 012 11032 Atta ch to Ear th Gro un d G R A V I T A T I O N A L T O R S I O N B A L A N C E A P 8 2 1 5 ...

Page 2: ...echanism must be fully raised on both sides when moving or transporting the Gravitational Torsion Balance Note Save the packing material from the interior of the box and re install this material when moving or transporting the Gravitational Torsion Balance ...

Page 3: ...tational Alignment of the Pendulum Bob Arms Zeroing 5 Setting up for the Experiment 6 Measuring the Gravitational Constant 7 Overview of the Experiment 7 Method I Measurement by Final Deflection 7 Theory 7 Procedure 9 Analysis 10 Method II Measurement by Equilibrium Positions 11 Theory 11 Procedure 11 Analysis 11 Method III Measurement by Acceleration 12 Theory 12 Procedure 13 Analysis 13 Maintena...

Page 4: ...urn of equipment for warranty repair belongs to the customer Equipment must be properly packed to prevent dam age and shipped postage or freight prepaid Damage caused by improper packing of the equipment for return shipment will not be covered by the warranty Shipping costs for returning the equipment after repair will be paid by PASCO scientific Equipment Return Should the product have to be retu...

Page 5: ...us The gravitational attraction of every object to every other object however is anything but obvious Despite the lack of direct evidence for any such attraction between everyday objects Isaac Newton was able to deduce his law of universal gravitation However in Newton s time every measurable example of this gravita tional force included the Earth as one of the masses It was therefore impossible t...

Page 6: ...n Additional Required Laser light source such as the PASCO OS 9171 Helium Neon Laser Meter stick A tt a c h to E a r th G r o u n d G R A V I T A T I O N A L T O R S I O N B A L A N C E A P 8 2 1 5 1 5 kg Tungsten masses Adapter rings Plasticdemonstration plate Replacement torsion ribbon Zero adjust knob Torsionribbon head Aluminum plate Leveling feet Pendulum mirror Optical grade glass window Lar...

Page 7: ...Gravitational Torsion Balance from the box and secure it in the base 3 Remove the front aluminum plate by removing the thumb screws Figure 3 and carefully remove the packing foam from the pendulum chamber Note Save the packing foam and reinstall it each time the Gravi tational Torsion Balance is transported 4 Fasten the clear plastic plate to the pendulum chamber with the thumbscrews Note Do not t...

Page 8: ...rew Figure 6a 2 Adjust the height of the pendulum by moving the torsion ribbon head up or down so the base of the pendulum is flush with the floor of the pendulum chamber Figure 6b 3 Tighten the retaining Phillips head screw Note Vertical adjustment is only necessary at initial setup and when you change the torsion ribbon or if someone has loosened the retaining screw by mis take it is not normall...

Page 9: ... 5 Rotationally align the pendulum arm a Raise the locking mechanisms by turning the locking screws until both of the locking mechanisms barely touch the pendu lum arm Maintain this position for a few moments until the oscillating energy of the pendulum is dampened b Carefully lower the locking mechanisms slightly so the pen dulum can swing freely If necessary repeat the dampening exercise to calm...

Page 10: ...m Note Avoid jarring the apparatus during this setup procedure 2 Attach copper wire to the grounding screw Figure 11 and ground it to the earth 3 Place the adapter rings on the support arm and place the large tung sten masses on the adapter rings and rotate the arm to Position I Figure 12 taking care to avoid bumping the case with the masses 4 Allow the pendulum to come to resting equilibrium You ...

Page 11: ...ent of the light spot on the scale as the light beam is deflected by the mirror Any of three methods can be used to determine the gravitational constant G from the motion of the small masses In Method I the final deflection method the motion is allowed to come to resting equilibrium a process that requires several hours and the result is accurate to within approxi mately 5 In Method II the equilib...

Page 12: ...comes to rest at a new equilibrium position S2 Figure 14 At the new equilibrium position S2 the torsion wire will still be twisted through an angle but in the opposite direction of its twist in Position I so the total change in angle is equal to 2 Taking into account that the angle is also doubled upon reflection from the mirror Figure 15 S S2 S1 or The torsion constant can be determined by observ...

Page 13: ...the measurement 3 Carefully rotate the swivel support so that the large masses are moved to Position II The spheres should be just touching the case but take care to avoid knocking the case and disturbing the system Note You can reduce the amount of time the pendulum requires to move to equilibrium by moving the large masses in a two step pro cess first move the large masses and support to an inte...

Page 14: ... second force is shown in Figure 17 the vector arrows shown are not proportional to the actual forces From Figure 17 The force F0 is given by the gravitational law which trans lates in this case to and has a component ƒ that is opposite to the direction of the force F This equation defines a dimensionless parameter that is equal to the ratio of the magnitude of ƒ to that of F Using the equation F ...

Page 15: ...th it as soon as possible in order to minimize the risk that the system will be disturbed between the two mea surements Waiting more than a day to perform step 3 is not advised Analysis 1 Construct a graph of light spot position versus time for both Position I and Position II You will now have a graph similar to Figure 18 2 Find the equilibrium point for each configuration by analyzing the corresp...

Page 16: ...nal force on the small masses as they did in Position I but now in the opposite direction Since the equilibrating force from the torsion band has not changed the total force Ftotal that is now acting to accelerate the small masses is equal to twice the original gravitational force from the large masses or Each small mass is therefore accelerated toward its neighboring large mass with an initial ac...

Page 17: ... of the procedure detailed in Method I 2 Immediately after rotating the swivel support observe the light spot Record the position of the light spot S and the time t every 15 seconds for about two minutes Analysis 1 Construct a graph of light spot displacement S S S1 versus time squared t2 with t2 on the horizontal axis Figure 20 Draw a best fit line through the observed data points over the first ...

Page 18: ...Thread the ribbon through the shaft 8 Using the zero adjust knob align the bottom tab with the face of the pendulum bob 9 Tighten the Phillips screw on the top of the balance to secure the torsion ribbon head 10 Attach the bottom tab of the ribbon to the pendulum bob using the Phillips screw 11 Replace the back plate 12 Level and align the pendulum according to the instructions in the Equipment Se...

Page 19: ...xic Be careful not to drop the 1 5 kg masses Technical Support Feedback If you have any comments about the product or manual please let us know If you have any suggestions on alter nate experiments or find a problem in the manual please tell us PASCO appreciates any customer feedback Your input helps us evaluate and improve our product Contacting Technical Support Before you call PASCO technical s...

Page 20: ... Gravitational Torsion Balance Technical Support 16 012 11032C ...

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