• He gave ideas about gravity and motion
  • He proposed that gravity attracts objects towards the Earth (keeps stuff in the orbit)
  • Pendulum can be used to find the strength of gravity

Newton’s law of gravitation:

$$ F_g = G\frac{M_1 M_2}{d^2} $$

Where G is the gravitational constant, $M_1$ is the mass of the first object, $M_2$ is the mass of the second object, and $d$ is the distance between the two objects. The formula solves for the gravitational force($F_g$) which is the attractive force between two objects with mass. Unit is $\text{m}^2\text{kg}^{-2}$.

• Gravity is the force of attraction between two objects (hence it depends on masses and distances between the objects).
• The force is directly proportional to the product of the masses of $M_1$ and $M_2$, and inversely proportional to the square of the distances of $M_1$ and $M_2$ from their centers (blue arrow)
  • This is inverse square law
• The gravitational constant is $6.67 \times 10^{-11}$

Example using this law:

• If the distance between the earth and the moon is doubled, the attractive force would go down, because its inverse
• But the attractive force between the masses will go down by a factor of 4 instead of 2, because it is inversely squared.

How to find gravitational field strength:

• All objects attract other objects by producing a gravitational field (gravitational force per area)
• To find the gravitational field strength($g$) of an object, divide the formula above (newtons law of gravitation) by $M_2$

The formula is:

$$ g = \frac{GM_1}{d^2} $$

All info from this website - https://www.khanacademy.org/science/in-in-class11th-physics/in-in-phy-gravitation/in-in-gravity-newtonian/a/newtons-law-of-gravitation-ap1#:~:text=Newton's universal law of gravitation&text=Every object in the universe,along a line joining them.&text=The force is directly proportional,between their centers of mass.