Glossary
Circular Orbit
A special type of elliptical orbit where the orbiting object maintains a constant distance and speed from the central body.
Example:
Many artificial satellites are placed in a circular orbit around Earth for consistent communication coverage.
Distance
The separation between the centers of two objects, crucial for determining the strength of gravitational interaction.
Example:
The gravitational force between two asteroids significantly decreases as the distance between them increases.
Elliptical Orbit
An oval-shaped orbit where the orbiting object's speed varies, being faster when closer to the central body.
Example:
Halley's Comet travels in a highly elliptical orbit around the Sun, spending most of its time far away.
Energy Conservation (in Orbits)
The principle that the total mechanical energy (kinetic plus potential) of an orbiting object remains constant in the absence of non-conservative forces.
Example:
Understanding energy conservation in orbits allows physicists to predict a comet's speed at different points in its elliptical path.
Escape Velocity
The minimum speed an object must attain to completely break free from the gravitational pull of a celestial body and not fall back.
Example:
To launch a probe to Mars, it must reach Earth's escape velocity to leave our planet's gravitational influence.
Gravitational Constant (G)
The universal constant of proportionality in Newton's Law of Universal Gravitation, representing the strength of the gravitational force.
Example:
The value of the gravitational constant () is essential for calculating gravitational forces between any two objects.
Gravitational Force
The attractive force between any two objects with mass, directly proportional to the product of their masses and inversely proportional to the square of the distance between them.
Example:
The gravitational force between the Earth and the Moon keeps the Moon in its orbit.
Gravity
The attractive force between objects with mass.
Example:
An apple falling from a tree demonstrates the Earth's gravity pulling it downwards.
Inertia
The property of an object to resist changes in its state of motion; in orbits, it refers to the object's tendency to continue moving in a straight line.
Example:
A satellite in orbit continuously 'falls' towards Earth, but its forward inertia prevents it from hitting the surface.
Kinetic Energy in Orbits
The energy an orbiting object possesses due to its motion, calculated as $1/2 mv^2$.
Example:
As a planet moves faster closer to its star in an elliptical orbit, its kinetic energy in orbit increases.
Mass
A fundamental property of matter that quantifies its resistance to acceleration (inertia) and its gravitational attraction.
Example:
A bowling ball has significantly more mass than a tennis ball, making it harder to accelerate and exerting a stronger gravitational pull.
Orbit
The curved path an object takes around another object in space, typically due to gravitational attraction.
Example:
The Moon follows a stable orbit around the Earth, never crashing into it.
Orbital Velocity
The specific speed an object needs to maintain a stable orbit around a celestial body at a given distance.
Example:
A satellite must achieve a precise orbital velocity to avoid falling back to Earth or flying off into space.
Period
The time it takes for an orbiting object to complete one full revolution around the central body.
Example:
The period of Earth's orbit around the Sun is approximately 365 days, defining a year.
Potential Energy in Orbits
The energy an orbiting object possesses due to its position within a gravitational field, typically defined as $-GMm/r$.
Example:
A satellite farther from Earth has a higher (less negative) gravitational potential energy in orbit.
Solar System
A star and all the celestial objects, such as planets, moons, asteroids, and comets, that orbit it due to gravity.
Example:
Our Solar System includes the Sun, eight planets, and countless smaller bodies, all bound by the Sun's gravity.