Bio-physics question (pizza slicer)

[ChrisGreaves]

My neighbour Patty, chief guinea-pig in my pizza experiments, just dropped by and gave me a pizza-cutter.
It is a knife-edge sharp wheel, about four inches diameter, on a handle.
You've all seen them in use at your local pizza-parlour.

"Thanks", I say, excitedly running the wheel back-and-forth across my hand.
Patty pales in shock, something a trained nurse is not supposed to do.
"You'll cut yourself!" she says.
No I won't. And somehow I knew/sensed I couldn't.

If I were to drag the knife-edge across my hand, I'd bleed.
If I were to stab down onto my hand I would bleed.
But rolling the wheel across my hand is relatively safe.

So why does rolling the wheel across the pizza cut it?

[HansV]

Is the wheel really sharp as a knife? Somehow, I doubt it.

[DaveA]

Because if you press hard enough you will cut your hand as when cutting the pizza, the pan or cutting board is NOT giving in and allows the cutter to do it's job.

[ChrisGreaves]

Is the wheel really sharp as a knife? Somehow, I doubt it.

Yup! It's sharpened.
Bevelled edges, ground.
Looks pretty good.

Don't tell Patty but after she cautioned me, I was a bit scared, but only for a second or two, once I realized nothing had happened [/bravado]

[ChrisGreaves]

Because if you press hard enough you will cut your hand as when cutting the pizza, the pan or cutting board is NOT giving in and allows the cutter to do it's job.

Thanks Dave.
When I press the wheel on my hand (a) I don't press that hard and (b) my hand yields a tad, there's only my own arm muscles holding it back.
I see now: It's not only the cutting-board that's not giving in, it's the kitchen counter, the apartment, the building, and about 6 quadrillion kilograms tons of rock.

[John Gray]

So why does rolling the wheel across the pizza cut it?

Because it's called a pizza-cutter, perhaps? (Function follows name...)

[BobH]

Surgeons describe their operations by using the terms "sharp and blunt dissection." I believe the pizza cutter wheel falls into the latter category.