Difference Between Gravity and Electromagnetism

Table of Contents

Main Difference – Gravity vs. Electromagnetism

Gravity and electromagnetism are two of the four fundamental forces in physics. Out of the four fundamental forces, these two are most familiar to us. The main difference between gravity and electromagnetism is that gravity is a force between masses whereas electromagnetism is a force between charges.

What is Gravity

Gravity refers to the force of attraction between masses. It is one of the four fundamental forces, responsible for objects on Earth always falling down, for The Moon’s motion around The Earth, and The Earth’s motion around The Sun. It was Sir Isaac Newton who first managed to describe gravity mathematically when he realized that the motion of an apple falling from a tree and the motion of The Moon around The Earth are both due to an attraction between those objects and The Earth. His law of gravitation states that if two objects having masses $m_1$ and $m_2$ are separated by a distance $r$ , the gravitational attraction between them is given by:

$F=\frac{Gm_1m_2}{r^2}$

Where $G$ is the universal gravitational constant $G=\mathrm{6.67\times 10^{-11}\;m^3\:kg^{-1}\:s^{-2}}$ . Later, Einstein’s work showed that Newton’s theory of gravity was incomplete. Today, gravity is explained using Einstein’s theory of general relativity. In Einstein’s theory, gravity is described as a curvature of space-time.

Difference Between Gravity and Gravitation - General_relativity

In general relativity, gravity is thought to be a result of warped space-time around massive objects.

Out of the four fundamental forces, gravity is the most difficult force to unify with the other three types of forces. It is also comparatively much weaker compared to the other three types (the strong force, the weak force and electromagnetism).

What is Electromagnetism

Electromagnetism is the force that exists between charges. Electrostatic forces may exist between charges which are at rest, and when charges move, they may create magnetic fields around themselves. So, moving charges may exert electrostatic forces as well as magnetic forces between each other. If a particle with a charge $q$ is moving with a velocity $\vec{v}$ through a region that has an electric field with strength $\vec{E}$ and a magnetic field with strength $\vec{B}$ , then the force $\vec {F}$ on the particle is given by:

$\vec{F}=q\left( \vec{E}+\vec{v}\times\vec{B}\right)$

Electromagnetism is responsible for electricity and the attraction between magnets. It is also responsible, at a subtle level, for keeping you on a chair without you falling through it. Under the Standard Model of particle physics, electromagnetism is described as being mediated by particles called photons.

Difference Between Gravity and Electromagnetism

What they act on

Gravity acts on masses.

Electromagnetism acts on charges.

Relative Strength

Electromagnetism is about 1035 times stronger than gravity [1].

Nature of Interaction

Gravity is always attractive.

Electromagnetism can be attractive or repulsive.

Shielding Ability

It is possible to shield spaces from electromagnetic forces.

There is no way to shield spaces from gravitational forces.

References:

Hughes, S. (2005, February 1). Introduction; Couloumb’s law; Superposition; Electric energy. Retrieved November 03, 2015, from MIT – Massachusetts Institute of Technology

Image Courtesy:

“Illustration of spacetime curvature.” by User:Johnstone (Created using an image of planet earth from NASA’s Galileo spacecraft.) [CC BY-SA 3.0], via Wikimedia Commons

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