They don't have to be. Tornadoes that form under dry conditions may lack a funnel. Tornadoes usually have funnels because they pull in moist air from other parts of the parent thunderstorm. The pressure drop in the tornado produces a temperature drop, which in turn triggers condensation.
Not sure what you mean by a funnel tornado. If you are referring to the Seymour, Texas tornado of April 10, 1979, it had a well-defined funnel and it was funnel-shaped. However, it did touch down so it was not merely a funnel cloud.
tornado clouds
A tornado that does not touch the ground is a funnel cloud.
A funnel cloud is like a tornado only it does not reach the ground.
A funnel cloud is a developing tornado that has not reached the ground.
Yes. A tornado is often visible as a funnel cloud as it develops.
A tornado starts out as a funnel cloud.
The "eye" of a tornado is at the center of the funnel.
To some extent, yes. A funnel cloud is the visible portion of a tornado. However, not all funnel clouds are tornadoes. If the winds associated with a funnel cloud do not reach the ground then it is not a tornado. Conversely, if the winds do reach the ground the term funnel cloud is not usually used, and the event is simply called a tornado.
A tornado has actually touched down on the ground - a funnel cloud is a spinning cloud that has not actually touched the ground.
In a sense, yes. But the term funnel cloud usually means a "tornado" that has not touched down.
A tornado that has touched the ground is called a funnel cloud.