How does the gravitational force between Earth and the Moon change when the distance between the two objects doubles but mass doesn't change?

The gravitational force between Earth and the Moon would stay the same.
The gravitational force between Earth and the Moon would goes up by a proportional amount.
The gravitational force between Earth and the Moon would go down by a proportional amount.
The gravitational force between Earth and the Moon would completely disappear

1 answer

The gravitational force between two objects, such as the Earth and the Moon, is described by Newton's law of universal gravitation, which states that the force \( F \) between two masses \( m_1 \) and \( m_2 \) is inversely proportional to the square of the distance \( r \) between them:

\[ F = G \frac{m_1 m_2}{r^2} \]

where \( G \) is the gravitational constant.

If the distance between the Earth and the Moon doubles (\( r \) becomes \( 2r \)), the gravitational force changes as follows:

\[ F' = G \frac{m_1 m_2}{(2r)^2} = G \frac{m_1 m_2}{4r^2} = \frac{1}{4} F \]

This means the gravitational force becomes one-fourth of the original force when the distance doubles.

Therefore, the correct answer is:

The gravitational force between Earth and the Moon would go down by a proportional amount.