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I saw this question on another site. It asked if a pizza cutter could cut fabric. which is not what I ask. A pizza cutter stays stationary wrt the underground while a straight knife moves. In both cases, though you can exert the same pressure. So why not use a straight knife when cutting a pizza?

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    $\begingroup$ Have you ever tried to cut a pizza with a normal knife? It's much easier to use a pizza cutter :) $\endgroup$
    – jumbot
    May 29 at 11:03
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    $\begingroup$ I eat pizza without cutting :) $\endgroup$
    – SG8
    May 29 at 11:06
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    $\begingroup$ @SG8 Indeed, the best way! :-) Though sometimes my mouth is too small... $\endgroup$ May 29 at 11:11
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    $\begingroup$ What kind of pizza cutter? There are the pizza wheel cutters that many people use at home to cut pizza, but there are also very long curved knives (aka a short sword, up to 20 inches long!) that people use in restaurants to very quickly cut pizza into slices with perfectly straight lines. Safely storing a pizza wheel cutter at home is easy. Doing so at home with 14 to 20 inch long knife is problematic. $\endgroup$ May 29 at 13:33
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    $\begingroup$ Forget physics theory. Have you actually tried it? The knife drags all the toppings! $\endgroup$
    – user253751
    May 29 at 19:41
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Well, I can think of the following reasons:

First, it is much easier to exert considerable vertical force on the pizza cutter because the point of contact falls close to the hand, thus minimizing the torque on it (as compared to a long knife). This increases the efficacy of the pressure-based method of cutting (it requires considerably more pressure than the usual, sliding method)

Second, the convex shape of the cutter means that the force is applied along a small portion of the edge. This is again useful in pressure cutting.

Third, the cutter is faster, especially when performing long straight cuts with multiple orientations, such as one needs to do when dividing a pizza in wedges.

Fourth, it is easy to make sure that one leaves out no parts along the line of cut were the cut has not been performed, or only imperfectly so. And even if one makes the cuts a bit shallow, they will tend to be more uniformly so, and thus allowing one to finish them off securely by pulling a little bit. This would be more difficult to ensure with the knife, as one would need to reset its position several times assuming the pressure-based method of cutting was chosen.

Which brings me to the fifth and most crucial point. The sliding method of cutting is not the most adequate because of the following points:

  1. The pizza must be fixed somehow so that it does not slip when cutting, which is inconvenient due to its thinness. Imagine placing a fork on a certain point to stabilize it. If the cut is long enough, at some point along the cut the fork will be far away from the contact point of the knive and, if the knive is on the downstream side, the pizza portion may tend to wrinkle, especially if it is one of those very thin ones. Furthermore, one avoids the ugly puncture marks left behind by the fork.

  2. Second, the sliding motion may drag some of the looser topings, such as olives or salame slices. This is very hard to avoid when there is a generous amount of molten mozzarella beneath them.

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    $\begingroup$ I will never cut a pizza in the same way anymore! $\endgroup$ May 29 at 12:55
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    $\begingroup$ Thank God you won’t! $\endgroup$ May 29 at 13:08
  • $\begingroup$ Re as compared to a long knife. Pizza restaurants typically do use a very long knife, longer than the diameter (circular pizzas) / length (rectangular pizzas) of the largest pizza that the restaurant serves. The knife is curved and has handles on both ends so that the pizza can be sliced in one fell swoop with a rocking motion. $\endgroup$ May 29 at 13:42
  • $\begingroup$ @DavidHammen Yes, but in this case with two handles the torque issue is not a problem. $\endgroup$ May 29 at 13:44
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    $\begingroup$ the last paragraph 2 is exactly why $\endgroup$
    – user253751
    May 29 at 19:41

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