Gravity — Science definition

Defined in 2 courses:

Where it is taught

In use

Gravity is an attractive interaction between objects with mass.

Gravity & Friction

An orbiting object has velocity while gravity continually changes that velocity.

Gravity, Orbits & Tides

Questions using gravity

Problem 1

Explain why a feather falls slower than a rock through air, even though gravity pulls on both.
Answer and explanation

Air resistance pushes up on the feather much more relative to its weight, because of its large surface area and very low mass, which slows its fall a lot. In a vacuum with no air resistance, a feather and a rock would actually fall at the same rate.

Problem 2

In the no-drag throw with initial horizontal velocity 6 m/s, what are horizontal velocity, vertical velocity and vertical acceleration at the top? Does gravity stop acting?
Answer and explanation

Horizontal velocity 6 m/s; vertical velocity 0; vertical acceleration −10 m/s². Gravity continues acting downward.

Separate the two velocity components.

Distinguish zero vertical velocity from zero acceleration.

Response criteria

  • State all three values with units.
  • Keep gravity downward.
  • Avoid claiming zero total velocity.

Problem 3

Independent check: In the no-drag throw with initial horizontal velocity 6 m/s, what are horizontal velocity, vertical velocity and vertical acceleration at the top? Does gravity stop acting?
Answer and explanation

Horizontal velocity 6 m/s; vertical velocity 0; vertical acceleration −10 m/s². Gravity continues acting downward.

Separate the two velocity components.

Distinguish zero vertical velocity from zero acceleration.

Response criteria

  • State all three values with units.
  • Keep gravity downward.
  • Avoid claiming zero total velocity.

Problem 4

Tidal effects depend on differences across EarthTidal effects depend on differences across EarthMoonCompare lunar acceleration with Earth-center accelerationNear side: stronger lunar acceleration than Earth’s center.Far side: weaker lunar acceleration than Earth’s center.Relative effects produce two bulges in the simplified equilibrium model.
Original exaggerated equilibrium-tide geometry. Red arrows represent relative sizes of Moonward lunar acceleration at selected Earth positions, not actual force values. The elongated outline summarizes an ideal two-bulge model; real coastal tides depend on rotation, basins, coastlines and dynamics.
Interpret the supplied visual model. How can the far-side relative effect be outward from Earth’s center while lunar gravity there still points toward the Moon?
Answer and explanation

The far side accelerates toward the Moon less than Earth’s center does. In the Earth-following comparison, that difference is away from the center, while the actual lunar attraction remains Moonward.

All red lunar-attraction arrows point toward the Moon, with different magnitudes. The far-side bulge is not drawn as lunar gravity pulling away from the Moon.

The far side accelerates toward the Moon less than Earth’s center does. In the Earth-following comparison, that difference is away from the center, while the actual lunar attraction remains Moonward.

Response criteria

  • Read the labeled quantities, reference frame or objects correctly.
  • Explain the relation between the visual evidence and the mechanism.
  • Keep the drawing’s stated assumptions and limits in the conclusion.

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