The arrow at the marked point aims at Earth's center. Soren says the force on a rock held there would act toward Earth's center. Is Soren correct?
A stone dropped in Chile, in Norway, or in your backyard falls toward the ground every time. A drawing of Earth's field has to say so, at every point at once.
Field lines carry arrows. For a gravitational field, the arrows all make the same promise.
Here is Earth's gravitational field. Every line points in, toward Earth.
The direction comes straight from what the lines mean. The line's direction at a point is found with a small mass placed at that point. A small mass placed at a point to probe the field is called a test mass.
The field exerts a force on the test mass, toward Earth, wherever the point is. The line's arrow shows that force's direction. So the arrow points toward Earth.
Which way do the gravitational field lines around Earth point?
The same holds for any mass's field. The Moon creates a gravitational field, and its lines point toward the Moon. Jupiter creates one too: the field exerts a force on a test mass near Jupiter, toward Jupiter, so the line through that point runs toward Jupiter.
Which way do the gravitational field lines around Mars point?
That is why the stone falls the same way on every continent. At every point, the local line points toward Earth's center, and the force on the stone acts that way.
A test mass is placed at a point near a planet. What is it for?
What does the direction of a gravitational field line show?
An asteroid has its own gravitational field. Which way do the field lines around the asteroid run?
At point P above a planet, the field pulls a 1 kilogram test mass down at the planet. Which way does the field line at P point?