Force of Gravity Equation
Reference from the original Physics I textbook.
- Force of Gravity Equation
For a spherical planet, the magnitude of gravitational acceleration at distance r from its center is g = GM/r². Near Earth’s surface, g ≈ 9.81 m/s² and the vector g⃗ points downward.
- Related Glossary Terms
Free body diagrams↗, Gravitational Force Equation, Gravitational Potential Energy Equation, Gravity, Potential Energy↗, Terminal Velocity
- Index
Chapter 1 - Newton’s Laws and FBDs
Chapter 1 - For Future Reference - Forces as Vectors
Reviewed physics notes (1)
These corrections keep the original lesson’s purpose while fixing errors in the source edition.
- The source omits the square on r and equates a vector to a scalar. — Reference 1
Glossary and deeper reading · 4 refreshers
These editorial refreshers supplement the reading. Definitions and examples are added guidance; original source wording and recorded answers remain in their original context.
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Force
A force describes an interaction that can change an object’s momentum. It is a vector measured in newtons, so both size and direction matter when forces are added. For example, a rope can pull a cart while the floor exerts friction in another direction.
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Gravity
Gravity is the attractive interaction between masses in the Newtonian model. For spherical bodies or point-mass approximations, its strength decreases with the square of the separation between their centers. For example, Earth’s gravity provides the inward force that keeps a satellite in orbit.
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Free-body diagram
A free-body diagram shows the external forces acting on one selected object or system. Each arrow names a real interaction, and its direction is the direction of that force. For example, a book resting on a desk has a downward gravitational force and an upward normal force; velocity is not an extra force arrow.
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Potential energy
Potential energy describes energy associated with the configuration of interacting parts of a system. Its numerical zero is a chosen reference, while differences in potential energy determine physical energy changes. For example, separating Earth and a ball changes their gravitational potential energy even though the energy belongs to their interaction.