Final answer:
The needle used for tough tissue is a suture needle. It is designed to easily penetrate and close wounds with sutures during surgical procedures, as it is sturdy and sharp.
Step-by-step explanation:
The needle used for tough tissue that is difficult to penetrate is called a suture needle. This type of needle is specifically designed to pass through tough, dense tissues during surgical procedures. Unlike hypodermic needles which are used to inject substances into the body, or biopsy needles used to take tissue samples, or spinal needles used for procedures involving the spinal canal, suture needles are sturdy and sharp to easily penetrate and close wounds with sutures.
Pressure is related to the sharpness of a knife and its ability to cut because a sharper blade will have a smaller surface area at the point of contact, allowing it to exert a greater amount of pressure per unit area than a dull blade. Similarly, when considering why a dull hypodermic needle hurts more than a sharp one, it is due to the same principle of pressure and surface area. A sharp needle has a very fine point, which concentrates the force applied into a very small area, allowing it to penetrate the skin easily. On the other hand, a dull needle has a blunter point, requiring more force to penetrate the skin, and thus causing more pain as the pressure is distributed over a larger area.