It stays moving because of newtons first law witch states. An object at rest will stay at rest unless acted upon by an outside force. Witch is why the bucket stays still. But it could move if an unbalanced force affects to to move and fall over. Or if someone bumps into it than it would be in motion becuase someone acted upon it.
How is this bucket not moving ?
The van stays in motion because of newtons first law witch states that an object in motion will stay in motion unless an outside force effects it. Witch is why the van is able to stay in motion. There are able to stop once an outside force becomes an unbalanced force and can stop this and keep it at rest.
How does the van stay in motion
Newtons Second Law
You can find out bu using newtons second law. You find the fore acceleration mass and fore of an objet. It can be used to find gravty.
How do you find out home much gravity is acting on us ?
You can find it by using newtons second law witch alows you to find the acceration of an object and find their mass.