Glossary
Acceleration due to gravity (g)
The acceleration experienced by an object due to the gravitational pull of a massive body, typically Earth, in a vacuum (approximately 9.8 m/s² on Earth).
Example:
When you drop a ball, it accelerates downwards at approximately 9.8 m/s² due to Earth's acceleration due to gravity.
Astronomical scales
Refers to the vast distances and immense masses involved in celestial bodies and systems, where gravity becomes the primary governing force.
Example:
The formation of galaxies and the orbits of planets around stars are phenomena best understood on astronomical scales.
Direct Relationship (Mass and Force)
A relationship where two quantities increase or decrease together; in gravitation, as the mass of objects increases, the gravitational force between them also increases proportionally.
Example:
If you double the mass of one object, the gravitational force between it and another object will have a direct relationship and also double.
Electromagnetic Force
One of the four fundamental forces, responsible for interactions between electrically charged particles, including light and magnetism.
Example:
A magnet sticking to a refrigerator is an everyday demonstration of the electromagnetic force.
Electroweak Force
One of the four fundamental forces, a unified description of the electromagnetic and weak forces, involved in processes like radioactive decay.
Example:
The decay of a neutron into a proton, electron, and antineutrino is governed by the electroweak force.
Force of Gravity (Weight)
The specific gravitational force exerted on an object by a celestial body, calculated as the product of its mass and the acceleration due to gravity ($F_g = mg$).
Example:
An astronaut's weight on the Moon is less than on Earth because the Moon has a smaller acceleration due to gravity.
Fundamental Forces
The four basic interactions that govern all phenomena in the universe: strong, electromagnetic, weak (electroweak), and gravitational forces.
Example:
Understanding the interplay of the fundamental forces helps physicists explain everything from atomic structure to the expansion of the universe.
Gravitational Fields
A region of space around a massive object where another massive object would experience a gravitational force, often represented by field lines.
Example:
The Earth creates a gravitational field around it, which is why objects fall towards its center.
Gravity
A fundamental force of nature that causes attraction between any two objects with mass.
Example:
The force of gravity pulls a dropped apple towards the Earth.
Infinite range
A property of gravity indicating that its influence extends indefinitely, never truly reaching zero, though its strength diminishes with distance.
Example:
Even light-years away, a star's gravitational pull, however tiny, still has an infinite range.
Inverse Relationship (Distance and Force)
A relationship where one quantity increases as the other decreases; in gravitation, as the distance between objects increases, the gravitational force between them decreases.
Example:
The further a satellite is from Earth, the weaker the gravitational pull it experiences, demonstrating an inverse relationship with distance.
Inverse square relationship
A relationship where the strength of a force or field is inversely proportional to the square of the distance from its source.
Example:
If you move twice as far from a light source, the light intensity drops to one-fourth, illustrating an inverse square relationship.
Long-range force
A force whose influence extends over vast distances, diminishing in strength but never truly becoming zero, such as gravity.
Example:
The Sun's gravitational pull, a long-range force, keeps Earth in orbit millions of miles away.
Newton's Law of Universal Gravitation
States that every particle in the universe attracts every other particle with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers ($F = G \frac{mM}{r^2}$).
Example:
Using Newton's Law of Universal Gravitation, we can calculate the force keeping the International Space Station in orbit around Earth.
No negative mass
The concept that mass, which is the source of gravity, is always positive, ensuring that gravitational forces are always attractive and cannot cancel each other out like electric charges.
Example:
Unlike electric charges where positive and negative can neutralize, the universe has no negative mass, meaning gravity always adds up.
Short-ranged forces
Forces whose influence diminishes very rapidly with distance, effectively becoming zero outside a very small range, such as within an atomic nucleus.
Example:
The short-ranged forces like the strong nuclear force are why atomic nuclei are so tightly bound but don't affect objects meters apart.
Strong Force
One of the four fundamental forces, responsible for binding protons and neutrons together within the atomic nucleus, acting over very short distances.
Example:
The strong force is what prevents the positively charged protons in an atom's nucleus from repelling each other and flying apart.
Weight vs. Mass
Mass is a measure of the amount of matter in an object, while weight is the force of gravity acting on that mass.
Example:
An astronaut's mass remains constant whether on Earth or the Moon, but their weight changes due to different gravitational pulls.