deck 3: gravity & orbits

Gravity

The force that pulls objects towards each other.

Examples of gravity

Keeps moons orbiting planets and planets orbiting stars.

Relationship between mass and gravity

More mass means a stronger gravitational pull.

2D model of gravity

Mass creates a dent in spacetime.

3D model of gravity

Mass curves spacetime inward.

Orbit

The elliptical path of an object around a larger body.

Shape of an orbit

An ellipse, not a perfect circle.

How does an orbit form?

Gravity pulls an object inward while its sideways speed keeps it missing the larger body.

Why doesn't a planet fall into the Sun?

Its sideways speed balances gravity, creating a stable orbit.

Stable orbit

A continuous state of falling towards a larger body while constantly missing it due to sideways speed.

Eccentricity

A measure of how stretched or elongated an orbit is.

What does eccentricity measure?

The shape of an orbit.

What does eccentricity NOT measure?

Orbit size or orbital speed.

What does an eccentricity of 0 mean?

A perfect circle.

What happens as eccentricity approaches 1?

The orbit becomes more stretched or elongated.

Low eccentricity

An orbit that is almost a perfect circle.

High eccentricity

A very stretched or elongated orbit.

Earth's eccentricity

About 0.017, so Earth's orbit is nearly circular.

Comets' eccentricity

Usually high, giving them very elongated orbits.

Why do comets have highly elongated orbits?

They have high eccentricity.