Orbital Motion

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Orbit Noun

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[or-bit]

Back

Orbit

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A continuous, curved path that a celestial body or spacecraft takes around a star, planet, or moon.

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Example: The image shows the Moon's orbit, a curved path around Earth, created by the balance between its forward velocity and Earth's inward pull of gravity.

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Gravity Noun

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[grav-i-tee]

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Gravity

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The universal force of attraction that exists between any two objects with mass, pulling them toward each other.

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Example: This image shows that gravity is a mutual force of attraction between two objects, like the Earth and another celestial body, pulling them toward each other.

Front

Centripetal Acceleration Noun

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[sen-trip-i-tl ak-sel-er-ay-shun]

Back

Centripetal Acceleration

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The acceleration of an object moving in a circular path, which is always directed toward the center of the circle.

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Example: An object moving in a circle has a velocity (blue arrow) tangent to the path, but its acceleration (red arrow) always points toward the center.

Front

Centripetal Force Noun

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[sen-trip-i-tl fors]

Back

Centripetal Force

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A force that acts on a body moving in a circular path and is directed toward the center of rotation.

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Example: An object moving in a circle has an inward-pulling force, the centripetal force, that keeps it from flying away in a straight line.

Front

Angular Velocity Noun

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[ang-gyuh-ler vuh-los-i-tee]

Back

Angular Velocity

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The rate at which an object rotates or revolves about an axis, measured in radians per unit of time.

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Example: Using the right-hand rule, if your fingers curl in the direction of rotation, your thumb points in the direction of the angular velocity vector.

Front

Radian Noun

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[ray-dee-an]

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Radian

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A unit of angle, equal to an angle at the center of a circle whose arc is equal in length to the radius.

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Example: This diagram shows that a radian is an angle in a circle where the length of the arc is equal to the length of the circle's radius.

Front

Period Noun

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[peer-ee-ud]

Back

Period

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The time it takes for an object to complete one full cycle of its motion, such as a single orbit.

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Example: This diagram shows the Earth's complete orbit around the Sun, which defines its orbital period, and also illustrates how its axial tilt causes seasons.

Front

Orbital Velocity Noun

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[or-bi-tl vuh-los-i-tee]

Back

Orbital Velocity

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The velocity at which a body revolves around another, which must be balanced with gravity to maintain an orbit.

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Example: This diagram shows a satellite's orbital velocity (V) as its forward speed, which is balanced by Earth's gravitational pull (F) to keep it in orbit.

Front

Free-fall Noun

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[free-fawl]

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Free-fall

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The motion of an object where gravity is the only significant force acting upon it, creating apparent weightlessness.

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Example: An object dropped (copper coin) and one pushed sideways (silver coin) are both in free-fall, so gravity makes them hit the ground simultaneously.

Front

Geosynchronous Orbit Noun

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[jee-oh-sing-kruh-nuhs or-bit]

Back

Geosynchronous Orbit

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An Earth-centered orbit with a period matching Earth's rotation, causing a satellite to stay over the same point on the equator.

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Example: A satellite travels in an inclined orbit that takes 24 hours to complete, matching the time it takes for the Earth to rotate once.