Newton’s Law of Gravitation: Understanding the Force That Holds Us Down

Gravity is one of the most fundamental forces in the universe. It keeps planets in orbit, makes objects fall, and even plays a role in shaping the cosmos. Sir Isaac Newton, in the 17th century, formulated the law of universal gravitation, explaining how objects attract each other. His discovery changed the way we understand motion and the universe itself.

What is Newton’s Law of Gravitation?

Newton’s law of gravitation states that every mass in the universe attracts every other mass with a force that is directly proportional to their masses and inversely proportional to the square of the distance between them. This means that larger objects have stronger gravitational pulls, and as objects move farther apart, the force weakens.

Mathematically, it is written as:

F=Gm1m2r2F = G \frac{{m_1 m_2}}{r^2}

where:

FF is the gravitational force between two objects
GG is the gravitational constant (6.674 × 10⁻¹¹ Nm²/kg²)
m1m_1 and m2m_2 are the masses of the objects
rr is the distance between them

This equation applies to everything—from apples falling from trees to planets revolving around the Sun.

The Story Behind the Discovery

The famous story of Newton and the apple has been told countless times. According to legend, Newton was sitting under an apple tree when an apple fell. This led him to wonder why objects always fall straight down. He connected this idea with the motion of the Moon around Earth. Eventually, this thought process helped him develop the law of gravitation.

Though the apple story might be exaggerated, it represents the kind of thinking that led to Newton’s discoveries. He combined observations, mathematics, and logical reasoning to create one of the most important scientific laws.

Examples of Gravity in Everyday Life

Gravity is something we experience all the time. Here are a few common examples:

Falling Objects: When you drop a pen, it falls to the ground because of gravity.
Jumping and Landing: No matter how high you jump, gravity pulls you back down.
Rivers Flowing: Water in rivers moves downhill due to the gravitational pull of Earth.
Tides in the Ocean: The Moon’s gravity affects ocean tides on Earth.

Newton’s Law of Gravitation in Space

Without gravity, planets would not stay in their orbits. The Earth is constantly moving around the Sun due to the gravitational pull between the two bodies. The same principle applies to moons orbiting planets.

One of the best cinematic examples of gravity in space is Christopher Nolan’s movie "Interstellar" (2014). In the film, the characters land on a planet near a black hole where time moves differently due to extreme gravitational forces. The way gravity is depicted in the movie aligns with real physics principles.

Comparing Gravity on Different Planets

Gravity is not the same everywhere. Different planets have different gravitational strengths based on their mass and size.

Earth: 9.8 m/s² (the standard we are used to)
Moon: 1.62 m/s² (about one-sixth of Earth’s gravity)
Mars: 3.71 m/s² (about one-third of Earth’s gravity)
Jupiter: 24.79 m/s² (much stronger than Earth’s gravity)

Astronauts on the Moon could jump much higher than on Earth because the Moon’s gravity is weaker. This is why astronauts seem to move in slow motion in footage from the Apollo missions.

Why is Newton’s Law Still Important?

Even though Einstein’s theory of relativity later expanded on gravity, Newton’s law is still widely used. Engineers, scientists, and astronomers rely on it for calculations involving planetary motion, spacecraft trajectories, and everyday physics applications.

Final Thoughts

Newton’s law of gravitation explains one of the most fundamental forces in nature. It applies to everything—from apples falling to space travel. His discovery shaped modern physics and helped us understand the universe better. Whether on Earth or in deep space, gravity is always at work.