Signe says her textbook has a gravitational field around it, far too weak to notice. Is Signe correct?
Earth attracts the Moon from 380,000 km away. The Sun attracts Earth from 150 million km away. Which objects, exactly, get to do the attracting? Is it only the giant ones?
You have seen that any object with mass has a gravitational field, and that gravity only ever attracts. Here is the full claim.
Every object with mass attracts every other object with mass. This is called universal gravitation: universal, because no mass sits it out.
Earth and the Moon attract each other: Earth exerts a gravitational force on the Moon, and the Moon exerts a gravitational force on Earth.
The same holds for small things. Two books standing on a shelf attract each other. Each book attracts the other with a tiny gravitational force. The force is far too small to see, but real.
And the Sun and Mars attract each other across empty space.
A student says two loaves on a bakery shelf exert no gravitational pull on each other. Is the student correct?
A tennis ball lies near a brick. Does the brick attract the tennis ball?
Write down the fact:
Every object with mass attracts every other object with mass.
The brick has mass, and the tennis ball has mass.
Yes: the brick attracts the tennis ball, and the ball attracts the brick.
Nell says her backpack pulls on Earth. Is Nell correct?
Does the tennis ball also attract Earth?
Write down the fact:
Every object with mass attracts every other object with mass.
The ball has mass, and Earth has mass.
Yes: the ball attracts Earth, just as Earth attracts the ball.
Sometimes the gravitational force is obvious, and sometimes it is far too small to notice. The force is never absent.
Which statement about gravitation is correct?
Two small asteroids drift in deep space, far from any planet or star. Which statement describes them?
A library book stands beside a globe. Which statement is correct?