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Laparoscopy is a minimally invasive surgical procedure where small surgical instruments are inserted into the body through cannulas (hollow tubes 0.5 to 1.0 cm in diameter) . A cannula is inserted into the skin while sleeved around a trocar (Figure 1) . The skin incision can be made directly with a sharp-tipped trocar as it is being inserted with the cannula. If a blunt-tipped trocar is used, the incision is made beforehand with a surgical blade. After insertion, the trocar is removed, leaving the cannula as an access point for laparoscopic procedures.
Figure 1 Cannula, trocar, and two types of tipsLow-friction trocars increase surgical precision and reduce postoperative scarring. Friction between the skin and trocar tip is tested with synthetic skin and a stationary ramp whose surface is made of the same material as the trocar. For testing, the synthetic skin is pressed against the ramp's surface by a load, weighted to allow the skin to slide down at a constant speed (Figure 2) . In this setup, the weight of the synthetic skin layer is negligible.
Figure 2 Experimental setup to test the friction between trocar and skin
Adapted from W. Firme-Gustavo et al., (C) 2015 Society of Laparoendoscopic Surgeons.
-For equally sized trocar-cannula systems, incisions made for blunt-tipped trocars are smaller than those made by sharp-tipped trocars, forcing the skin to stretch more around the cannula. This option better prevents slipping after the cannula is inserted because:

Question

Passage
Laparoscopy is a minimally invasive surgical procedure where small surgical instruments are inserted into the body through cannulas (hollow tubes 0.5 to 1.0 cm in diameter) . A cannula is inserted into the skin while sleeved around a trocar (Figure 1) . The skin incision can be made directly with a sharp-tipped trocar as it is being inserted with the cannula. If a blunt-tipped trocar is used, the incision is made beforehand with a surgical blade. After insertion, the trocar is removed, leaving the cannula as an access point for laparoscopic procedures.

Figure 1 Cannula, trocar, and two types of tipsLow-friction trocars increase surgical precision and reduce postoperative scarring. Friction between the skin and trocar tip is tested with synthetic skin and a stationary ramp whose surface is made of the same material as the trocar. For testing, the synthetic skin is pressed against the ramp's surface by a load, weighted to allow the skin to slide down at a constant speed (Figure 2) . In this setup, the weight of the synthetic skin layer is negligible.

Figure 2 Experimental setup to test the friction between trocar and skin
Adapted from W. Firme-Gustavo et al., (C) 2015 Society of Laparoendoscopic Surgeons.
-For equally sized trocar-cannula systems, incisions made for blunt-tipped trocars are smaller than those made by sharp-tipped trocars, forcing the skin to stretch more around the cannula. This option better prevents slipping after the cannula is inserted because:

Quizplus · Accepted Answer

11ecba2d_12ef_4cb5_a3bf_cf9841327c71_MD0008_00 Static friction is the frictional force that prevents two surfaces from sliding. After the cannula is inserted, static friction between the cannula and skin prevents slipping because static friction counters the forces that promote sliding. Static friction has an upper limit, and if the forces that promote sliding exceed this value, slipping occurs. The upper limit of static friction F_s is the product of the coefficient of static friction μ_s and the normal force N (the perpendicular force one surface exerts on the other): F_s = μ_sN The greater the upper limit of static friction, the better the cannula is prevented from slipping (Choice B). Therefore, slipping can be better prevented by increasing the normal force. The normal force keeping the cannula in place is due to the skin pressing on the cannula. According to the question, cannulas inserted with blunt-tipped trocars experience greater stretching of the skin. Therefore, the cannula is subject to a greater normal force, producing a greater static frictional force. (Choice A) According to the question, the cannulas are of equal size, and therefore the sizes of the contact areas are the same. (Choice D) The coefficient of static friction depends only on the properties of the surfaces involved, and therefore it will not change. Educational objective: Friction is the force that resists sliding between two surfaces, and static friction prevents surfaces from sliding. The maximum value of static friction is proportional to the normal force, which is the perpendicular force one surface exerts on the other. Therefore, greater stretching of skin creates a greater normal force around a cannula and greater static friction to better prevent slipping.

Passage Laparoscopy Is a Minimally Invasive Surgical Procedure Where Small Surgical