Concept understanding — Gravitational Field Direction
Gravitational Field Direction: From Intuition to Precision
Imagine you're holding a ball in your hand. The moment you let go, it falls straight down toward the floor. Not sideways, not up — straight down. That "down" direction is the direction of the gravitational field at that point.
Now picture yourself on the other side of the Earth — in Australia, for instance. If you drop a ball there, it also falls "down" — but from your perspective, that "down" is toward the ground beneath your feet, which points toward the centre of the Earth. So the direction of the gravitational field is always toward the centre of the Earth.
This is the core intuition: gravity pulls things toward the source of the field.
The Precise Statement
Important
The gravitational field at any point in space points directly toward the mass that creates it. For a point mass M, the field direction is radially inward — along the line joining the point to M, pointing from the point toward M.
Mathematically, if you place a test mass m at a position r relative to a source mass M, the gravitational field g at that point is:
g=−r2GMr^
Here:
r^ is a unit vector pointing away from M (radially outward).
The minus sign flips that direction: the field points towardM (radially inward).
So the direction of g is always toward the source mass.
Why "Toward the Source"?
Think of a single massive object — say, the Sun. A small rock anywhere near the Sun feels a pull straight toward the Sun's centre. If you place the rock to the left of the Sun, it gets pulled right. If you place it above, it gets pulled down. The pull is always along the line connecting the rock to the Sun's centre, and it always points toward the Sun.
This is because gravity is a central force — it acts along the line joining two masses, and it's always attractive. There's no repulsive gravity.
What About Multiple Masses?
If you have two or more masses (like the Earth and the Moon), the net gravitational field at a point is the vector sum of the fields from each mass. The direction of the net field is the direction of that sum — it points toward the combined effective centre of all the masses, weighted by their distances and sizes.
For example, on the surface of the Earth, the Moon's gravity also pulls on you, but it's much weaker than Earth's. So the net field points almost exactly toward Earth's centre, with a tiny tilt toward the Moon.
Note
The direction of the net gravitational field is not necessarily toward the centre of the nearest large mass — it's the vector sum of all contributions. But in most everyday situations, Earth's field dominates, so "down" is toward Earth's centre.
Same / Similar Concept — real previous-year questions on the same or a closely similar concept, not this exact question.
CBSE 2025Set ANNUAL1 markMCQ
Q.Gravitational intensity inside a spherical shell at any point is
(A) zero
(B) infinity
(C) same as on the outer surface
(D) none of these
›Reveal solutionSolution
The gravitational intensity anywhere inside a uniform spherical shell is exactly zero.
For a thin uniform spherical shell of mass M and radius R, Newton's shell theorem gives the gravitational field intensity at a distance r from the centre as:
For r>R (outside): g=r2GM (acts as if all mass concentrated at centre)