Module 4: Gravity and Newton's Discoveries

Frame of Reference

Coordinate system tied to an observer watching an object move.

Galilean Relativity

Motion and speed depend on the observer's frame of reference.

Inertia

The natural tendency of an object to resist changes in motion.

Newton's First Law of Motion

Objects keep moving steadily unless acted on by an unbalanced force.

Newton's Second Law of Motion

Net force equals mass multiplied by acceleration (F = m * a).

Mass

The quantitative ratio of net force divided by acceleration (m = F / a).

Weight

The downward gravitational force pulling on a mass at a specific location.

Newton's Third Law of Motion

Every applied action force has an equal and opposite reaction force.

Henry Cavendish

The scientist who first measured the universal gravitational constant using lead spheres.

Universal Law of Gravitation

Every mass attracts every other mass through an inverse-square distance force.

Free Fall

Downward falling where gravity accelerates objects at 9.8 meters per second squared.

Newton's Cannon

High horizontal speed lets an object curve around Earth without hitting it.

Escape Velocity

The minimum speed needed to break free from a body's gravitational pull.

Centripetal Force

The inward pull needed to keep an object moving in a circle.

Differential Gravity

The difference in gravitational pull between near and far sides of a body.

Tidal Bulges

Two opposite watery bulges created on Earth by the Moon's gravity.

Tidal Braking

Ocean friction against the seabed that gradually slows Earth's daily rotation rate.

Tidal Locking

Synchronous rotation where the Moon's spin matches its orbital period around Earth.

Center of Mass

The shared balance point that two orbiting space bodies circle around.

Reflecting Telescope

A telescope design that uses curved mirrors instead of glass lenses.

Refracting Telescope

An older telescope design that uses glass lenses to bend light.

Chromatic Aberration

Color halos blurring an image caused by glass bending light wavelengths unequally.

Visible Spectrum

The natural rainbow band of colors that make up white sunlight.

If ramp steepness increases, does a rolling ball move slower?

False, steeper slopes dilute gravity less, making the ball roll down faster.

What extraterrestrial feature did Galileo first measure using shadows?

Mountains on the Moon.

If a rocket has twice the thrust and half the mass, acceleration?

It achieves 4 times the acceleration.

If distance between two masses doubles (2x), gravity becomes?

It drops to one-fourth (1/4th) of its original strength.

If distance between two masses quadruples (4x), gravity becomes?

It drops to one-sixteenth (1/16th) of its original strength.

Does gravity depend more on an object's mass or separation distance?

Distance, because distance is squared in the bottom of the formula.

What happens to an astronaut who pushes off a spaceship?

She stays in Earth orbit alongside the craft rather than falling.

Why do astronauts float inside an orbiting space station?

The astronaut and station are in continuous free fall together.

If planet mass increases 36x at identical radius, escape speed becomes?

It becomes 6 times larger because escape speed scales with square root.

How does Earth's pull on the Moon compare to Moon's pull on Earth?

They pull on each other with precisely equal and opposite force.

Why do reflecting telescopes eliminate color blurring?

Mirrors bounce all colors of light equally without bending them through glass.

If telescope mirror diameter quadruples (4x), light power increases by?

It collects 16 times more light because area scales with diameter squared.