Independent: A tornado, often known as a twister in the US, is a spinning column of air that joins a cloud (normally the moisture-rich cumulonimbus) and the ground.
Yesterday's tornado in Moore, Oklahoma was said to be at least two miles wide - the biggest are about three miles wide. The accumulated debris at its heart, including cars, simply adds to the devastating force with which it smashes through everything in its path.
Their speed across the ground and the duration of the 'touchdown' are other factors...