The Moon circles Earth once a month, on a near-circular orbit. Nothing is tied to the Moon. No road touches it, and no wall presses on it. Yet its path bends around Earth the whole way, so a net force must point from the Moon toward Earth, at the orbit's center.
Which force can act across all that empty space?
Of the forces you have met, one acts without touching: gravity. Earth's gravitational pull on the Moon points from the Moon straight toward Earth. And Earth sits at the center of the Moon's orbit.
So Earth's gravitational pull on the Moon points at the orbit's center. That pull is the net inward force the orbit requires. Gravity supplies the Moon's centripetal force.
A weather satellite circles Earth the same way. Earth's gravitational pull on the satellite points toward Earth, at the center of its orbit, and supplies the satellite's centripetal force.
Earth itself circles the Sun. The Sun's gravitational pull on Earth points toward the Sun, at the center, and supplies Earth's centripetal force.
Now take a ball whirling on a level cord beside you. Gravity acts on the ball too. But Earth's pull on the ball points down at the ground, not at the center of the ball's horizontal circle. Here gravity is not the supplier; the cord's tension is.
So the direction decides it. Gravity supplies the centripetal force only where the gravitational pull points at the circle's center. For an orbiting body it always does, because the attracting body sits at the center.
Jupiter's moon Europa circles Jupiter on a near-circular orbit. Which force supplies Europa's centripetal force?
The International Space Station circles Earth on a near-circular orbit. Which force supplies the station's centripetal force?
Nothing touches the station on its orbit.
Earth's gravitational pull on the station points toward Earth, at the center of the orbit.
The net force toward the center is the centripetal force.
Earth's gravitational pull supplies the station's centripetal force.
Mars circles the Sun on a near-circular orbit. Pavel says: 'The Sun's gravitational pull on Mars supplies Mars's centripetal force.' Is he correct?
A communications satellite fires no engines, yet it keeps circling Earth. Which force holds it on its circular path?
The satellite needs no forward force to keep moving. It needs an inward force to keep turning.
Earth's gravitational pull on the satellite points toward Earth, at the center of the orbit, and turns the path at every instant.
Earth's gravitational pull supplies the satellite's centripetal force. No engine is needed.
A GPS satellite circles Earth. The force supplying the satellite's centripetal force is the gravitational pull of which object on which object?
In which case does gravity supply the centripetal force?
A space telescope circles Earth on a near-circular orbit. Which force supplies the telescope's centripetal force?
Gravity acts on every object near Earth. In which situation does gravity supply an object's centripetal force?