Glossary
Acceleration due to gravity (g)
The acceleration experienced by an object solely under the influence of gravity, representing the strength of the gravitational field at a specific location. Near Earth's surface, its approximate value is 9.8 m/s².
Example:
When you drop a ball, it speeds up at a rate of 9.8 m/s² due to the acceleration due to gravity.
Always Attractive
A characteristic property of gravitational force, meaning it exclusively pulls objects towards each other and never pushes them apart.
Example:
No matter how far apart, two masses will always experience an always attractive gravitational pull towards each other.
Centripetal Force
A net force that acts on an object moving in a circular path, directed towards the center of the circle, causing the object to continuously change direction. In orbital motion, gravity often provides this force.
Example:
For a satellite to maintain its orbit around Earth, the Earth's gravity provides the necessary centripetal force.
Direct Proportionality
A relationship where two quantities increase or decrease together at a constant ratio. In gravity, the force is directly proportional to the product of the masses, meaning if one mass doubles, the force doubles.
Example:
If a spaceship's mass doubles, the gravitational force between it and a planet will show direct proportionality by also doubling.
Force of Gravity (Weight)
The specific gravitational force exerted on an object by a large celestial body, typically calculated as the product of the object's mass and the local acceleration due to gravity. This force is also commonly referred to as weight.
Example:
Your weight on Earth is the force of gravity acting on your mass, pulling you downwards.
Free-Body Diagram (FBD)
A visual tool used in physics to analyze the forces acting on a single object, representing the object as a point mass and drawing all external forces acting on it as vectors originating from that point. Gravitational force is almost always included.
Example:
When analyzing a block sliding down a ramp, drawing a free-body diagram helps visualize the normal force, friction, and gravitational force acting on it.
Gravitational Constant (G)
The universal constant of proportionality in Newton's Law of Universal Gravitation, with a value of approximately 6.67 x 10^-11 N·m²/kg². It quantifies the fundamental strength of the gravitational interaction.
Example:
The incredibly small value of the gravitational constant explains why you don't feel a significant gravitational pull from your nearby classmates.
Gravitational Force
A fundamental force of attraction that exists between any two objects possessing mass. It is responsible for phenomena ranging from objects falling to Earth to the orbits of planets.
Example:
The force that keeps the Moon orbiting Earth, preventing it from flying off into space, is the gravitational force.
Gravitational Potential Energy
The energy an object possesses due to its position within a gravitational field. It represents the work done against gravity to move an object to a certain height or distance from a gravitational source.
Example:
A roller coaster at the very top of its highest hill has maximum gravitational potential energy before it begins its thrilling descent.
Inverse-Square Relationship
A relationship where one quantity is inversely proportional to the square of another. In gravity, the force decreases rapidly as the distance between objects increases; doubling the distance quarters the force.
Example:
The rapid decrease in light intensity as you move away from a bulb is analogous to the inverse-square relationship of gravity with distance.
Long-Range Force
A type of force that can act on an object without direct physical contact, working over a distance. Gravity is the primary example of a long-range force in AP Physics 1.
Example:
Unlike pushing a cart, the Earth's pull on a high-altitude weather balloon is a long-range force.
Newton's Universal Law of Gravitation
A fundamental law stating that the gravitational force between any two objects is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers.
Example:
Using Newton's Universal Law of Gravitation, scientists can precisely calculate the force between a distant exoplanet and its star.