History of Astronomy and Newtonian Mechanics

Vocabulary flashcards covering Galileo's astronomical discoveries, telescope developments, and Newton's fundamental definitions and laws of motion.

Galileo Galilei

An Italian experimental scientist who first carefully evaluated measurement uncertainties, discovered the law of inertia decades before Newton, showed all objects fall at the same rate without air resistance, and used the telescope to make astronomical discoveries that refuted the geocentric model.

Hans Lepersche

A Dutch eyeglass maker credited with inventing the telescope around 1604 or 1608 with an initial magnification of 3 to 4 times.

Phases of Venus

Galileo's telescopic observation that Venus undergoes a complete cycle of phases (from new to crescent to gibbous to full) while changing apparent size by approximately 6.2 times, proving that Venus orbits the Sun rather than the Earth.

Moons of Jupiter

Four bright points of light discovered orbiting Jupiter (such as Io orbiting every $1.77$ days and Europa every $3.54$ days), disproving the geocentric claim that all celestial orbits must be centered on the Earth.

Sunspots

Temporary dark blemishes on the Sun caused by magnetic field concentrations that impede the upwelling of hot gas; their tracking proved the Sun is not unchanging and that it rotates independently of Earth's periods (about $33$ days at the equator and $38$ days at the poles).

Dialogue of the Two Worldviews

A controversial book written by Galileo in everyday Italian structured as a debate between a heliocentrist, a moderator, and a geocentrist named Simplicio, which ultimately led to Galileo's trial and conviction for heresy.

Refracting Telescope

A type of telescope that relies on multiple precisely ground, transparent curved glass lenses placed in front of one another to gather and focus light.

Reflecting Telescope

A telescope invented by Isaac Newton that uses a curved primary mirror and a flat secondary mirror instead of lenses to focus light, avoiding internal glass imperfections and enabling larger apertures.

Speed

The rate of change of distance with time, defined mathematically as $\frac{\Delta d}{\Delta t}$; a scalar quantity measuring how fast an object is moving regardless of direction.

Velocity

A vector quantity that specifies both the speed of an object and the direction in which it is traveling.

Acceleration

The rate of change of velocity with respect to time ($a = \frac{\Delta v}{\Delta t}$), measured in units of $\text{m/s}^2$, which occurs whenever an object speeds up, slows down, or changes direction.

Acceleration Due to Gravity ($g$)

The constant downward acceleration experienced by freely falling objects near the surface of the Earth, equal to approximately $9.8\,\text{m/s}^2$.

Force

A push or pull exerted on an object in a specific direction that, when unbalanced, causes a mass to accelerate.

Vector

A physical measurement or quantity that has both a numerical magnitude and an associated direction, such as velocity, acceleration, and force.

Scalar

A physical quantity that has magnitude but no spatial direction, such as mass and speed.

Newton ($\text{N}$)

The standard metric unit of force, equivalent to $1\,\text{kg}\cdot\text{m/s}^2$, representing slightly less than one quarter of a pound ($\approx 0.25\,\text{lb}$).

Momentum

The tendency of a moving mass to maintain its current motion, calculated as mass times velocity ($p = mv$) with units of $\text{kg}\cdot\text{m/s}$ in the same direction as the velocity.

Newton's First Law of Motion

The physical principle that an object remains at rest or continues moving in a straight line at constant speed unless acted upon by an unbalanced force.

Unbalanced Force

A net, non-zero force resulting from unequal opposing forces acting on a body, which produces a change in the body's speed, direction, or both.

Newton's Second Law of Motion

The rule stating that the acceleration of an object is directly proportional to the applied unbalanced force and inversely proportional to its mass ($a = \frac{F}{m}$ or $F = ma$).

Newton's Third Law of Motion

The rule that for every action force exerted by one object onto a second object, there is always an equal and opposite reaction force exerted by the second object back onto the first.