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Summary of Contents for PASCO AP-8215
- Page 1 012-06802B Instruction Manual and 11/98 Experiment Guide for the PASCO scientific Model AP-8215 GRAVITATIONAL TORSION BALANCE © 1998 PASCO scientific $7.50...
- Page 2 Gravitational Torsion Balance 012–06802B Note: To avoid breaking the torsion ribbon, the locking mechanism must be fully raised on both sides during moving or transporting the Gravitational Torsion Balance. Note: Save the packing material from the interior of the chamber, and re-install this material during moving or transporting the Gravitational Torsion Balance.
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Page 3: Table Of Contents
012–06802B Gravitational Torsion Balance Contents Section Page Copyright and Warranty Information ..................ii Introduction..........................1 A Little Background ......................1 Equipment ..........................2 Equipment Parameters ...................... 3 Equipment Setup ........................3 Initial Setup ........................3 Leveling the Gravitational Torsion Balance ..............4 Vertical Adjustment of the Pendulum ................ - Page 4 PASCO will repair or replace at its option any part of following rules: the product which is deemed to be defective in material ➀...
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Page 5: Introduction
012-06802B Gravitational Torsion Balance head of Introduction torsion ribbon The PASCO scientific AP-8215 Gravitational Torsion Balance zero adjust knob reprises one of the great experiments in the history of physics— the measurement of the gravitational constant, as performed by Henry Cavendish in 1798. -
Page 6: Equipment
• replacement torsion ribbon (part no. 004-06788) • 2-56 x 1/8 Phillips head screws (4) • Phillips screwdriver (not shown) Additional Required: • laser light source (such as the PASCO OS-9171 He-Ne Laser) • meter stick torsion ribbon head 1.5 kg lead... -
Page 7: Equipment Parameters
012-06802B Gravitational Torsion Balance IMPORTANT NOTES Equipment Parameters ➤ The Gravitational Torsion Balance • Small lead balls is a delicate instrument. We Mass: 38.3 g + 0.2 g (m recommend that you set it up in a Radius: 9.53 mm relatively secure area where it is safe Distance from ball center to torsion axis: d = 50 .0 mm from accidents and from those who... -
Page 8: Leveling The Gravitational Torsion Balance
Gravitational Torsion Balance 012-06802B torsion ribbon Leveling the Gravitational Torsion Balance head 1. Release the pendulum from the locking mechanism by unscrewing the locking screws on the case, lowering the locking mechanisms to their lowest positions (Figure 4). torsion ribbon SIDE, CUTAWAY VIEW... -
Page 9: Rotational Alignment Of The Pendulum Bob Arms (Zeroing)
012-06802B Gravitational Torsion Balance 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 mistake; it is not normally done during each experimental setup. TOP, CUTAWAY VIEW Rotational Alignment of the Pendulum Bob Arms The pendulum bob arm must be centered... - Page 10 Gravitational Torsion Balance 012-06802B 3. Rotationally align the case by rotating it until the laser beam location of the projected laser projected from the glass window is centered on the metric beam from the glass scale (Figure 9). window location of the 4.
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Page 11: Setting Up For The Experiment
012-06802B Gravitational Torsion Balance grounding Setting up for the Experiment screw 1. Take an accurate measurement of the distance from the mirror to the zero point on the scale on the projection surface (L) (Figure 8). (The distance from the mirror surface to the outside of the glass window is 11.4 mm.) Note: Avoid jarring the apparatus during this setup procedure. -
Page 12: Method I: Measurement By Final Deflection
Gravitational Torsion Balance 012–06802B The enormous strength of the Earth's attraction for the small masses, in comparison with their attraction for the large masses, is what originally made the measurement of the gravitational constant such a difficult task. The torsion balance (invented by Charles Coulomb) provides a means of negating the otherwise overwhelming effects of the Earth's attraction in this experiment. - Page 13 012–06802B Gravitational Torsion Balance The gravitational attraction between the two small masses and their neighboring large masses produces a net torque ( ) on grav the system: = 2Fd (1.2) grav where d is the length of the lever arm of the pendulum bob crosspiece.
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Page 14: Procedure
Gravitational Torsion Balance 012–06802B The torsion constant can be determined by observing the period (T ) of the oscillations, and then using the equation: = 4 π I/ κ (1.6) where I is the moment of inertia of the small mass system. The moment of inertia for the mirror and support system for the small masses is negligibly small compared to that of the masses themselves, so the total inertia can be expressed as:... -
Page 15: Analysis
012–06802B Gravitational Torsion Balance 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 process: first move the large masses... - Page 16 Gravitational Torsion Balance 012–06802B geometry for this second force is shown in Figure 17 (the vector arrows shown are not proportional to the actual forces). Φ From Figure 17, f = F sinΦ sinΦ = + 4d Figure 17 Correcting the measured value of G The force, F is given by the gravitational law, which translates, in this case, to:...
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Page 17: Method Ii: Measurement By Equilibrium Positions
012–06802B Gravitational Torsion Balance METHOD II: Measurement by Equilibrium Positions Observation Time: ~ 90+ minutes Accuracy: ~ 5 % Theory When the large masses are placed on the swivel support and moved to either Position I or Position II, the torsion balance oscillates for a time before coming to rest at a new equilibrium position. -
Page 18: Method Iii: Measurement By Acceleration
Gravitational Torsion Balance 012–06802B the two equilibrium positions and record the result as Δ S. 3. Determine the period of the oscillations of the small mass system by analyzing the two graphs. Each graph will produce a slightly different result. Average these results and record the answer as T. - Page 19 012–06802B Gravitational Torsion Balance changed, the total force (F ) that is now acting to accelerate total the small masses is equal to twice the original gravitational force from the large masses, or: = 2F = 2Gm (3.2) total ΔS Each small mass is therefore accelerated toward its neighboring large mass, with an initial acceleration (a ) that is...
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Page 20: Procedure
Gravitational Torsion Balance 012-06802B acceleration (x = 1/2 at ), the acceleration can be calculated: = 2 Δ s/t = Δ Sd/t (3.6) By monitoring the motion of the light spot over time, the acceleration can be determined using equation 3.6, and the gravitational constant can then be determined using equation 3.4. -
Page 21: Maintenance
012-06802B Gravitational Torsion Balance ➁ Grasp the ➂ pendulum bob here Maintenance Loosen to stabilize it. the Phillips screw. Replacing the Torsion Ribbon Assembly If the torsion ribbon breaks, replace it as follows: 1. Remove the plates, and raise the locking mechanism using the locking screws until the pendulum arms are securely anchored (Figure 21a). -
Page 22: Transporting And Storing
Gravitational Torsion Balance 012–06802B Note: Be sure the ribbon is not twisted. Note: To avoid breaking the torsion ribbon, the locking 9. Tighten the Phillips screw on the top of the balance to mechanism must be fully raised secure the torsion ribbon head. on both sides during any moving or transporting of the 10. -
Page 23: Technical Support
If you have any information: suggestions on alternate experiments or find a problem in the manual, please tell us. PASCO ➤ If your problem is with the PASCO apparatus, appreciates any customer feedback. Your input note: helps us evaluate and improve our product.
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