### Mechanics

Schematic of system

1 nut                         2 angle knob

3 nut                         4 pointer disc

5 scale disk              6 screw

7 screw rod              8 wire

9 glass                     10 connector

11 connector           12 mirror

13 knob                   14 rest

15 small ball            16 damping box

17 damping piece   18 main body

19 swinging table    20 scale

21 base                   22 level

23 foot                     24 slide

25 support               26 large ball

27 pipe                    28 oil holder

29 screw                 30 screw

31 clip                     32 oil box

33 rest arm             34 screw rod

Plot of inverse square ratio

## LEMI-47 Cavendish Balance for Measuring Gravitational Constant

Features

• Clear physics concept

• Compact, stable, and reliable

• Affordable

Introduction

LEMI-47 is a compact instrument for measuring the gravitational constant and verifying the gravitational effect based on an elaborately designed Cavendish balance (torsion pendulum). It uses a reflected laser beam to monitor the damped harmonic oscillations of the balance with two large spherical masses in both positions. From the period of the oscillation, the position of the equilibria, and the geometry and masses involved, the phenomenon of the universal gravitation between objects can be qualitatively observed and the gravitational constant can be quantitatively measured.

Using this apparatus, the following experiments can be conducted:

1. Measure the inherent oscillating cycle of a torsion balance

2. Measure the gravitational constant with two methods: the final deflection method and the acceleration method

3. Verify the gravitational force between two objects is inversely proportional to the square of their distance

Specifications

 Description Specifications Mass of lead balls 2 large balls: 1.5 kg each,  mass difference between the two balls < 2.0 g 2 small balls: 20 g each,  mass difference between the two balls < 0.5 g Beam of torsion balance Length: 100 mm Wire of torsion balance Free torsion oscillating cycle: 580 ±10 s, length: 150 mm, area: 0.145 × 0.008 mm2 Damping medium Oil Uncertainty Measurement error of gravitational constant: < 15%

Accessory List

 Description Qty Large lead ball 2 Magnet bar 1 Support pipe 2 Slide 2 Leveling screw 3 Beryllium brass wire 5 Damping oil cylinder 1 Holder of cylinder 1 Screw for holder 1 Clamp 1 Screw for clamp 1 Nut for clamp 1 Oil bottle (damping oil) 1 Oil pipe 1

Schematic of system

1 nut                         2 angle knob

3 nut                         4 pointer disc

5 scale disk              6 screw

7 screw rod              8 wire

9 glass                     10 connector

11 connector           12 mirror

13 knob                   14 rest

15 small ball            16 damping box

17 damping piece   18 main body

19 swinging table    20 scale

21 base                   22 level

23 foot                     24 slide

25 support               26 large ball

27 pipe                    28 oil holder

29 screw                 30 screw

31 clip                     32 oil box

33 rest arm             34 screw rod

Plot of inverse square ratio