Which property gives an object a gravitational field?
Let go of a ball and it drops. No hand, no string. Nothing touches it, yet it picks up speed toward the ground.
The last lesson showed that any object with mass has a gravitational field around it. This lesson says what Earth's field does to objects inside it.
Now consider the ball just after it leaves your hand. It sits inside Earth's gravitational field. The ball has mass. The ball experiences a force: a pull toward Earth.
No contact is needed. The field already fills the space the ball falls through.
A skydiver has just left the plane. Does she experience a force in Earth's gravitational field?
Write down the fact:
In a gravitational field, any object with mass will experience a force.
The skydiver has mass, and she is inside Earth's field.
Yes: she experiences a force toward Earth.
A raindrop falls inside Earth's gravitational field. Does it experience a force?
A hawk gliding high above a valley has mass, so it experiences the force. A satellite far above the air has mass, so it experiences the force. And a parked truck has mass, so it experiences the force even while it sits still.
A kite hangs in the air on a windy day. Does Earth's gravitational field exert a force on the kite?
Write down the fact:
In a gravitational field, any object with mass will experience a force.
The kite has mass. The field acts on the kite whether or not it is falling.
Yes: the kite experiences a force toward Earth.
A soccer ball hangs at the top of its flight for an instant. Does it experience a force at that instant?
That is the dropped ball's whole story: it has mass, it sits inside Earth's gravitational field, so it experiences a force toward Earth.
A hot-air balloon drifts above a town. Which statement is true?
A climber's dropped water bottle falls toward the ground with nothing touching it. Why does a force act on the bottle?
A moth, a bus, and a cloud all sit inside Earth's gravitational field. Which of them experience a force?