You can beat the entire planet in a tug-of-war. Lift an apple. The entire Earth attracts the apple downward. Your one hand wins anyway.
This lesson profiles the first of the four fundamental forces: what it acts on, how far it reaches, and how strong it is.
You've already seen that any mass in a gravitational field experiences a force. That is the first line of gravity's profile: the gravitational force acts on everything with mass. A planet, an apple, and a single dust speck all feel it.
The second line of the profile gives the range: the gravitational force acts over unlimited range, growing weaker with distance but never reaching zero. Earth's gravitational force reaches the Moon. The Sun's gravitational force reaches Earth. Distance weakens the force; it never ends it.
The third line gives the strength: of the four fundamental forces, the gravitational force is by far the weakest.
The weakest sounds wrong. Gravity holds you down and keeps planets in orbit. But look at what that takes. It takes the whole Earth's mass to give a noticeable pull on an apple.
And your hand still beats it. A hand's grip is a contact force, electromagnetic at the particle level. That tiny patch of electromagnetic force beats the gravity of six septillion kilograms of planet.
Gravity only ever feels mighty because the masses involved are mighty. A bigger mass gives a bigger gravitational force, and planets and stars have enormous masses.
The Moon orbits about 380,000 km from Earth. Why does Earth's gravitational force still act at that distance?
The Moon has mass, so the gravitational force acts on it.
The gravitational force acts over unlimited range, growing weaker with distance but never reaching zero.
380,000 km weakens the force; it does not end it.
Earth's gravitational force still acts on the Moon. It is weaker at that distance, and it is not zero.
Two bowling balls sit 1 m apart on a shelf. Does a gravitational force act between them?
Both balls have mass, so the gravitational force acts between them.
The gravitational force is by far the weakest of the four fundamental forces.
Between ball-sized masses, the force is far too small to notice.
Yes. A gravitational force acts between the balls, but it is far too weak to notice.
The gravitational force acts on…
A space probe flies far beyond Pluto. Does Earth's gravitational force still pull on it?
Of the four fundamental forces, the gravitational force is…
A dust speck drifts in the air. What does Earth's gravitational force do to the speck?
A comet drifts farther and farther from the Sun. What happens to the Sun's gravitational pull on it?
Between two particles, gravity loses to every one of the other three forces. Yet the Sun holds eight planets in orbit. Why is the Sun's pull on a planet so large?