Glossary
Circular Motion
The motion of an object along the circumference of a circle or rotation along a circular path.
Example:
A satellite orbiting Earth is an example of circular motion, where gravity provides the necessary centripetal force.
Field Lines
Imaginary lines used to visualize a vector field, such as a gravitational field. Their direction indicates the direction of the force, and their density indicates the strength of the field.
Example:
Drawing field lines around a planet helps visualize that the gravitational force always points towards its center and is stronger closer to the surface.
Free Fall
A state of motion where the only force acting on an object is gravity, resulting in an acceleration equal to the local gravitational field strength.
Example:
A skydiver experiences free fall before deploying their parachute, accelerating downwards due to gravity alone.
Gravitational Field
A region of space surrounding a mass where another mass would experience a gravitational force. It is a vector field, indicating both magnitude and direction.
Example:
The Earth creates a gravitational field that extends far into space, influencing the orbits of satellites.
Gravitational Field Equation
The formula $g = G \frac{M}{r^2}$, which calculates the gravitational field strength at a point due to a mass M, at a distance r from its center.
Example:
Using the Gravitational Field Equation, we can calculate that the gravitational acceleration on Mars is less than on Earth due to its smaller mass and larger radius.
Gravitational Field Strength (g)
The magnitude of the gravitational force per unit mass at a given point, equivalent to the acceleration due to gravity at that location.
Example:
On Earth's surface, the gravitational field strength is approximately 9.8 N/kg, meaning a 1 kg object experiences a 9.8 N gravitational force.
Gravitational Force
The attractive force that exists between any two objects possessing mass. It is always directed towards the center of the masses involved.
Example:
When you jump, the Earth's gravitational force pulls you back down to the ground.
Gravitational Potential Energy
The energy an object possesses due to its position within a gravitational field, representing the work done against gravity to move it to that position.
Example:
A roller coaster at the top of a hill has maximum gravitational potential energy, which converts into kinetic energy as it descends.
Kinematics
The branch of mechanics concerned with the description of motion, without reference to the forces causing the motion.
Example:
When analyzing the trajectory of a projectile under gravity, you often use kinematics equations to determine its position and velocity over time.
Newton's Law of Universal Gravitation
A fundamental law stating that every particle attracts every other particle with a force directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers.
Example:
This law explains why the Sun's immense mass keeps planets in orbit, as the Newton's Law of Universal Gravitation dictates a strong attractive force.
Universal Gravitational Constant (G)
The proportionality constant in Newton's Law of Universal Gravitation, with a value of approximately $6.67 imes 10^{-11} Nm^2/kg^2$. It quantifies the strength of the gravitational interaction.
Example:
The value of Universal Gravitational Constant (G) is tiny, which is why gravitational forces are only significant between very massive objects.
Weight
The common term for the gravitational force exerted on an object by a celestial body, calculated as the product of the object's mass and the gravitational field strength ($F = mg$).
Example:
An astronaut's weight on the Moon is less than on Earth because the Moon has a smaller gravitational field strength.