...an ordinary lawnmower sucks air up into the mower body causing the grass to stand vertically, which allows the blade to slice evenly at the bottom of the grass.
To demonstrate this in another way, a vacuum hair clipper does the same thing. It sucks hair into it before it is cut so that a really precise cut can be made. The lifting of the grass is actually caused by the tab on the back of the mower blade which causes air lift and raises the grass up.
By filming a lawn mower in action with a super fast camera, that in turn gives wonderful slow motion, you can see the blades of grass being lifted up just before being cut.
As a further illustration of this principle, look up the hover-type lawn mower...it was a mower with no wheels, and a symmetrical, dish-shaped housing. The idea was that it could hover over the lawn, and small obstacles, and deliver a perfect cut. One popular model was the Flymo, and there were gasoline-engine hover mowers as well. They never really caught on, since they required considerable skill and unwavering attention...if you did hit an obstacle, the mower (and the operator) were likely to suffer significant damage.
As a further illustration of this principle, look up the hover-type lawn mower...it was a mower with no wheels, and a symmetrical, dish-shaped housing. The idea was that it could hover over the lawn, and small obstacles, and deliver a perfect cut. One popular model was the Flymo, and there were gasoline-engine hover mowers as well. They never really caught on, since they required considerable skill and unwavering attention...if you did hit an obstacle, the mower (and the operator) were likely to suffer significant damage.
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