Why is gravity so much weaker than other forces?

Gravity is about 10^36 times weaker than the electromagnetic force. This hierarchy problem is one of the biggest unsolved mysteries in physics. Gravity only dominates at large scales because matter is electrically neutral on average.

Does gravity travel at the speed of light?

Yes. According to general relativity, changes in the gravitational field propagate at the speed of light. The LIGO detector confirmed this in 2015 by detecting gravitational waves from merging black holes.

What is the difference between g and G?

G (big G) is the universal gravitational constant (6.674 × 10^-11). Little g is the local gravitational acceleration, which is 9.81 m/s^2 on Earth's surface but varies by location and altitude.

Why does gravity decrease with altitude?

Since F is inversely proportional to r^2, increasing distance from Earth's center reduces gravitational pull. At the altitude of the ISS (408 km), gravity is about 89% of surface gravity. Astronauts float because they are in free fall, not because gravity is absent.

What is escape velocity?

Escape velocity is the minimum speed needed to leave a gravitational field without further propulsion. For Earth it is 11.2 km/s. It depends on mass and radius: v_escape = sqrt(2GM/R).

Gravity Calculator

Calculate gravitational force between two masses

Gravity (Newton's Law)

F = G × m1 × m2 / r²

Mass 1 (kg)

Mass 2 (kg)

Distance (m)

Formula

F = G × m1 × m2 / r²

What Is Gravity?

Gravity is the fundamental force of attraction between any two objects with mass. On Earth's surface, gravity accelerates all objects downward at approximately 9.81 m/s² (g), regardless of their mass. This was famously demonstrated by Galileo, who showed that a feather and a cannonball fall at the same rate in a vacuum.

Newton's Law of Universal Gravitation describes the gravitational force between any two masses separated by a distance. It is an inverse-square law: double the distance and the force drops to one-quarter. Gravity governs everything from a dropped apple to the orbits of planets and the structure of galaxies.

How to Use the Gravity Calculator

Select the calculation type: gravitational force between two masses, or free-fall acceleration.
For gravitational force: enter mass 1, mass 2, and the distance between their centers in meters.
For free-fall: enter height (m) to calculate fall time and impact velocity.
Click Calculate to get force (N), fall time (s), and impact speed (m/s).

Formula & Explanation

Gravitational Force:
  F = G × m₁ × m₂ / r²

Free-fall time from height h:
  t = √(2h/g)

Impact velocity:
  v = g × t = √(2gh)

G = 6.674×10⁻¹¹ N·m²/kg²
g = 9.81 m/s² (Earth surface)

The gravitational constant G is extremely small, meaning gravity between everyday objects is negligible. Only when one mass is planetary scale does gravity become significant.

Worked Examples

Free Fall from a Building

An object is dropped from 50 m height. t = √(2×50/9.81) = √(10.19) = 3.19 s. Impact velocity = 9.81 × 3.19 = 31.3 m/s (≈ 113 km/h). The object hits the ground in about 3.2 seconds at highway speed.

Gravity Between Two People

Two 70 kg people stand 1 m apart. F = 6.674×10⁻¹¹ × 70 × 70 / 1² = 3.27×10⁻⁷ N. This is 0.33 micronewtons — completely imperceptible. Human-scale gravity is negligible compared to Earth's pull on us (686 N).

Earth-Moon Gravitational Force

Earth mass = 5.97×10²⁴ kg, Moon mass = 7.34×10²² kg, distance = 3.84×10⁸ m. F = 6.674×10⁻¹¹ × 5.97×10²⁴ × 7.34×10²² / (3.84×10⁸)² = 1.98×10²⁰ N. This enormous force keeps the Moon in orbit around Earth.

Frequently Asked Questions

Why do all objects fall at the same rate?▾

Heavier objects feel more gravitational force, but they also have more inertia resisting acceleration. These two effects cancel exactly, giving all objects the same acceleration g = 9.81 m/s² (in the absence of air resistance). This equivalence is a cornerstone of Einstein's general relativity.

How does gravity vary across Earth's surface?▾

g varies slightly: it's stronger at the poles (~9.83 m/s²) than at the equator (~9.78 m/s²) due to Earth's oblate shape and centrifugal effect of rotation. At the top of Mount Everest, g ≈ 9.77 m/s².

What is the escape velocity from Earth?▾

Escape velocity is the minimum speed needed to escape Earth's gravity without further propulsion: v_escape = √(2GM/R) = √(2 × 6.674×10⁻¹¹ × 5.97×10²⁴ / 6.371×10⁶) ≈ 11.2 km/s (40,320 km/h).

Is there gravity in space?▾

Yes — gravity extends infinitely. Astronauts in the ISS are in free fall around Earth (g ≈ 9 m/s² there). They feel weightless because both they and the ISS are falling at the same rate. There is no location in the universe completely free of gravity.

What is gravitational potential energy?▾

Near Earth's surface, PE = mgh, where m is mass, g = 9.81 m/s², and h is height above a reference. This energy is released as kinetic energy during free fall. At large distances, PE = −GMm/r (negative because gravity is attractive).