The Sun and Its Neighbors - Newton's Laws and Gravity

Vocabulary flashcards covering Newton's laws, gravity, orbits, and related concepts from the lecture.

Speed

The rate of change of position; the distance traveled per unit time (a scalar, measured by a speedometer).

Velocity

Speed with a direction; the combination of magnitude and direction (a vector).

Acceleration

The rate of change of velocity; can involve a change in speed, direction, or both.

Friction

A contact force that opposes motion and causes things to slow down or stop.

Newton's First Law

An object at rest stays at rest and an object in motion stays in motion unless acted on by an outside force.

Inertia

The resistance of any physical object to a change in its state of motion or rest.

Newton's Second Law

Acceleration is proportional to the net force and inversely proportional to mass; a = F/m (or F = m a).

Momentum

p = m v; a vector quantity that is conserved in a closed system (sum of momenta stays the same).

Angular Momentum

L = m v r (or I ω); a conserved vector quantity for rotating bodies.

Conservation of Momentum

In a closed system, the total momentum remains constant before and after interactions.

Conservation of Angular Momentum

In a rotating system, angular momentum remains constant; changes in radius affect angular velocity to keep L constant.

Kepler's Laws

Planets orbit the Sun in ellipses with the Sun at one focus; they move faster when closer to the Sun and slower when farther away.

Ellipse

A closed curve; in orbital motion, planets travel in an elliptical path with the Sun at a focus.

Gravity

The force of attraction between two masses; acts along the line joining their centers and depends on mass and distance.

Universal Law of Gravitation

F = G (m1 m2) / r^2; gravity depends on the product of masses and inversely on the square of the distance.

Gravitational Constant (G)

A tiny constant determined experimentally; its exact value is not explained by current theory.

Weight

The force of gravity on an object; equal to m g and varies with the local gravitational field (e.g., lighter on the Moon).

Free Fall

When the only force acting on an object is gravity; objects in free fall experience apparent weightlessness in space.

Escape Velocity

The minimum speed needed to break free from a body's gravitational field (Earth’s is about 36,000 km/h).

Circular Orbit

An orbit in which gravity provides the centripetal force, keeping an object in a closed, circular path.

Barycenter (Center of Mass)

The common center of mass around which two bodies orbit; for Pluto-Charon, the barycenter lies between them.

Tidal Locking

A situation where an object's rotation period matches its orbital period, so the same face always faces its partner.

Perihelion

The closest point of a planet's orbit to the Sun; at perihelion the planet moves fastest.