Cavendish's Experiment:
1. The Apparatus: He used a torsion balance, which consisted of a horizontal rod suspended by a thin wire. At the ends of the rod were two small lead spheres. Two larger lead spheres were positioned nearby, one on each side of the smaller spheres.
2. Measuring Gravitational Force: The gravitational attraction between the large and small spheres caused the rod to rotate slightly. Cavendish meticulously measured the angle of this rotation.
3. Calculating the Gravitational Force: He used the angle of rotation, the known distance between the spheres, and the properties of the wire to calculate the force of attraction.
4. Newton's Law of Universal Gravitation: Cavendish knew the force of attraction between the spheres depended on their masses and the distance between them. He also knew the value of the gravitational constant, which is a fundamental constant in physics. By rearranging Newton's Law of Universal Gravitation, he was able to solve for the mass of the Earth.
5. Calculating Density: He used the known mass of Earth and its volume (which was estimated at the time) to calculate the Earth's density.
Significance:
* Cavendish's experiment was the first to accurately measure the mass of Earth.
* It was a groundbreaking experiment that confirmed Newton's Law of Universal Gravitation and paved the way for further research in gravitation.
* It provided the first accurate estimate of the Earth's density.
Important Note: While Cavendish's experiment is often credited with determining Earth's density, it's crucial to remember that he actually calculated Earth's mass. The density was then derived using the calculated mass and a pre-existing estimate of Earth's volume.
