How are We Moving? - Scales of Motion

Vocabulary flashcards covering rotational motion, orbital motion, galactic motion, relative motion, and celestial reference frames from the APS 105 lecture notes.

Earth's Rotational Velocity at Hampton's Latitude

The speed at which Earth rotates at Hampton's latitude, calculated as $12,800\,\text{km} \times \pi \times \cos(\text{latitude}) = 33,700\,\text{km}$ per 24 hours, equal to $1,400\,\text{km/hr}$ ($800\,\text{mph}$).

Earth's Rotational Speed Variation by Latitude

The variation of rotational speed across Earth, spinning fastest at the equator ($1,650\,\text{km/hr}$) and slowest near the poles ($0\,\text{km/hr}$ at the pole).

Earth's Rotation vs. Revolution

Rotation refers to Earth spinning on its axis once per day, while revolution refers to Earth orbiting around the Sun once per year.

Earth's Orbital Velocity

The velocity of Earth revolving around the Sun, calculated as $9.4 \times 10^8\,\text{km} / 8760\,\text{hours} = 107,000\,\text{km/hr}$ (approximately $100,000\,\text{km/hr}$).

Sun's Galactic Orbit

The orbit of the Sun and solar system around the Galactic Center at a distance of $28,000\,\text{light-years}$, completing one full orbit every $230\,\text{million years}$.

Solar System's Galactic Velocity

The velocity of the Sun and solar system orbiting the Galactic Center, calculated as $28,000\,\text{LY} \times 2\pi / 230\,\text{million years} = 800,000\,\text{km/hr}$.

Hubble's Velocity-Distance Relation

Hubble's demonstration that a galaxy's speed relative to us depends on its distance, showing a linear relationship between galactic velocity in $\text{km/sec}$ and distance in $\text{MLY}$.

Relative Motion

The principle that movement can only be known by how an object's position changes relative to another reference object.

Celestial Reference Point

Reference objects in the sky, primarily stars, used to measure relative motion because they appear to remain in fixed relative positions night after night and year after year.

Scales of Motion Summary

The multiple simultaneous speeds of human motion: walking around campus ($4\,\text{km/hr}$), rotating with Earth ($1,400\,\text{km/hr}$), orbiting the Sun ($100,000\,\text{km/hr}$), and orbiting the Galactic Center ($800,000\,\text{km/hr}$).