Knives are pressure amplifiers. They take a modest amount pressure applied to the handle (PSI = pounds per square inch) and deliver the same amount of force over a much smaller area (the edge of the blade). That produces more pressure. The pounds stay the same but the number of square inches of area is much reduced resulting in a higher value of PSI. The sharper the knife the smaller the area of the knife edge and the higher the pressure.No bullet cuts anything. The permanent cavity is created by exceeding the leastic limits of the tissue and it tears.
Knives cut. Bullets tear.
Example--3 pounds of force applied to about 2 square inches of handle = 1.5PSI. 3 pounds of force applied to about .001 square inches = 3,000psi.
This very high pressure easily exceeds the elastic limits of the tissue contacted by the knife edge and it tears--but on a very small scale at the contact point of the blade edge.
Bullets don't need to amplify pressure since they already have a huge amount available. They tear the tissue they contact due to the application of high pressure. They do exactly the same thing as a knife but also have enough impact energy to create blunt trauma (the stretch cavity) as well.
If you could swing a knife as fast as a bullet travels, the result would be very similar in that you would get a temporary stretch cavity as well as a cutting type injury.