Formerly, to move heavy objects several logs of similar size were used that were placed under the object to be moved. This was pushed and the trunks rolled so that the object moved forward.
The drawing shows four identical trunks that have a circumference of 1 meter each.
When the trunks go full circle, How far will the load advance?
When the roller advances, the contact point they have with the object moves at the rate of one meter per full turn. However, since the trunks are also in contact with the ground, each meter also travels one meter from the ground so that the total displacement of the load will be the sum of both, that is: 2 meters.