Physics Lecture Notes: Gravity and Astronomy

Comprehensive vocabulary flashcards covering the history of gravity, Newtonian physics, planetary motion, and astronomical phenomena based on lecture notes.

Aristotle's theory of gravity

The early belief that things "want" to go back to where they came from, heavier objects fall faster, and objects in space move in perfectly circular orbits.

Galileo (1564-1642)

Performed tests that disapproved much of Aristotle’s theories, though he did not provide the mathematical proofs.

Isaac Newton (1643-1727)

Theorized that the forces acting on objects on Earth act the same way in space and developed the Law of Universal Gravitation.

Law of Universal Gravitation Formula

$$F = G \frac{m_1 m_2}{d^2}$$

Universal Newtonian Gravitational Constant (G)

The value based on the force of gravity of two $1\,kg$ masses, $1\,meter$ apart, equal to $6.67 \times 10^{-11}\,Nm^2/kg^2$.

Inverse Square Law

An explanation of the relationship where the effect of a phenomenon is reduced or increased by the inverse of the distance squared ($1/d^2$).

Black Hole size comparison

If the Sun underwent collapse and became a black hole, it would be approximately $6\,km$ in diameter with a radius of $3\,km$.

Apparent weightlessness

The condition experienced when there is zero support force (such as when a cable breaks in an elevator), despite gravity still being present.

Satellite minimum horizontal speed

The velocity required to orbit Earth horizontally above the atmosphere, which is $8\,km/s$ (approx. $18,000\,mph$).

Earth's curvature rate

The Earth "curves away" by $4.9\,m$ for every $8\,km$ traveled in any direction.

Gravitational pull through a uniform planet

If falling through a hole drilled through a planet of Earth's mass, an object reaches maximum velocity at the center (approx. $30,000\,mph$) and stops at the opening on the other side.

Hollow planet gravity

On the inside of a hollow sphere, one would feel apparent weightlessness everywhere because mass and distance squared effects cancel out.

Tidal forces (Moon)

The side of the Earth facing the moon experiences a $6.7\%$ greater gravitational pull than the sides facing away, causing tides.

Spring tide

Tides that occur every $14\,days$ when the Sun, Moon, and Earth are aligned, resulting in high high tides and low low tides.

Neap tide

Tides that occur every $14\,days$ when the Sun, Earth, and Moon are at $90\,degrees$, resulting in smaller tidal variations.

Geosynchronous orbit

An orbit located at $6.5$ earth radii (approx. $35,000\,km$) where a satellite takes $24\,hours$ to orbit and stays over the same location.

Elliptical orbit speed range

Occurs when a projectile is launched horizontally at a speed greater than $8\,km/s$ but less than $11.2\,km/s$.

Ptolemy (AD 100-170)

Developed a geo-centric model of the universe to try to explain retrograde motion.

Nicolaus Copernicus (1473-1547)

Introduced the modern helio-centric (Sun-centered) idea of the solar system.

Johannes Kepler (1571-1630)

Assistant to Tycho Brahe who used Brahe's data to develop the Three Laws of Planetary Motion.

Kepler's First Law

Each planet moves in an elliptical orbit with the Sun at one focal point.

Kepler's Second Law

A line from the planet to the Sun sweeps out equal areas of space in equal amounts of time.

Kepler's Third Law

The square of the times of revolutions (periods) of the planets are proportional to the cube of their distance (radius) from the sun ($T^2 \propto R^3$).

Escape Velocity

The speed required ($11.2\,km/s$ for Earth) to leave a planet's surface so that the object will never fall back.