Diagram to show how the inverse square law works.

Like the electrostatic force, the gravitational force is an inverse square law force.

Although gravitation is no longer on the AAMC's list for the new MCAT, the comparison and contrast of gravitational force with electrostatic force is so helpful to understanding that the subject remains as a supplemental chapter in this course. Both electrostatic force and gravitation are inverse square law forces. There are many important similarities in problem solving between gravitation and the electrostatic force. Learning a bit about gravitation will lay some important groundwork for understanding and modelling force and energy relationships. For many students, this will make electrostatics more accessible.

WikiPremed Resources

Gravitation Cards
Chapter from the Wisebridge Learning System for Physics

Gravitation Images
Image gallery for study with links to larger teaching JPEGs for classroom presentation

Question Drill for Gravitation
Conceptual Vocabulary Self-Test

Basic Terms Crossword Puzzle

Basic Puzzle Solution

Learning Goals


Memorize the Law of Universal Gravitation. (Knowing the value of the gravitational constant is not important).

Demonstrate the ability to solve basic quantitative problems involving gravitational force.

Develop an understanding of how an 'inverse square law' force operates in a basic, intuitive way.

Be able to describe the concept of gravitational field and understand how to conceptualize the field as a force per unit mass. Also be able to conceptualize the gravitational field as an acceleration.

Build the skill to imaginatively visualize changes in the gravitational potential energy between two masses. Understand the 'binding energy' of a gravitational system. Master the related concept of escape velocity.

Demonstrate the capability of applying the kinematics and dynamics of uniform circular motion along with the Law of Universal Gravitation to solve problems of circular orbit.

Understand how to use Kepler's Laws to predict basic behaviors of orbiting bodies.

Suggested Assignments

Because gravitation is not going to be directly tested, you don't need to spend a great deal of time. Studying the physics cards for gravitation should be sufficient.

Conceptual Vocabulary for Gravitation

Gravitation is a natural phenomenon by which all objects with mass attract each other.
Tides are the cyclic rising and falling of Earth's ocean surface caused by the tidal forces of the Moon and the Sun acting on the oceans.
Center of mass
The center of mass of a system of particles is a specific point at which, for many purposes, the system's mass behaves as if it were concentrated.
Gravitational field
The gravitational field around a single particle in classical mechanics is a vector field pointing directly towards the particle giving the magnitude of the force per unit mass for the array of points in space.
A orbit is the path that an object makes around another object while under the influence of a centripetal force such as gravity.
Escape velocity
Escape velocity is the speed where the kinetic energy of an object is equal in magnitude to its potential energy in a gravitational field.
General relativity
General relativity is the geometrical theory of gravitation published by Albert Einstein in 1915-16 unifying special relativity and Newton's law of universal gravitation.
Standard gravity
Standard gravity is the nominal acceleration due to gravity at the Earth's surface at sea level.
Gravitational binding energy
The gravitational binding energy of an object consisting of loose material, held together by gravity alone, is the amount of energy required to pull all of the material apart, to infinity.
Inverse-square law
An inverse-square law is any physical law stating that some physical quantity or strength decreases proportional to the square of the distance from the source of that physical quantity.
Cavendish experiment
The Cavendish experiment, performed in 1797 - 1798, was the first experiment to measure the force of gravity between laboratory masses.
Orbital period
The orbital period is the time it takes a planet (or another object) to make one full orbit.
Geosynchronous satellite
A geosynchronous satellite is a satellite whose orbital track on the Earth repeats regularly over points on the Earth over time.
Geosynchronous orbit
A geosynchronous orbit is an orbit around the Earth with an orbital period matching the Earth's sidereal rotation period.
Geostationary orbit
A geostationary orbit is a geosynchronous orbit directly above the Earth's equator, with orbital eccentricity of zero. From the ground, such an object appears motionless in the sky.
Circular orbit
A circular orbit is an elliptic orbit with the eccentricity equal to zero.
An ellipse is the locus of points on a plane where the sum of the distances from any point on the curve to two fixed points is constant.
Astronomical unit
The astronomical unit is a unit of length nearly equal to the semi-major axis of Earth's orbit around the Sun.
Perigee is the point at which an object in orbit around the Earth makes its closest approach to the Earth.
Kepler's laws of planetary motion
Johannes Kepler (1571 - 1630) was a German mathematician whose primary contributions to astronomy and astrophysics were his three laws of planetary motion.
Perturbation is a term used in astronomy to describe alterations to an object's orbit caused by gravitational interactions with other bodies.
An apsis is the point of greatest or least distance of the elliptical orbit of an astronomical object from its center of attraction.
Heliocentrism is the theory that the sun is at the centre of the Universe and/or the Solar System.
Low Earth orbit
A low Earth orbit is generally defined as an orbit within the locus extending from the Earth's surface up to an altitude of 2,000 km.
Specific orbital energy
The specific orbital energy of an orbiting body traveling through space is the sum of its potential energy and kinetic energy per unit mass.
Standard gravitational parameter
The standard gravitational parameter of a celestial body is the product of the gravitational constant and the mass.