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Chapter 11: Q9CQ (page 394)

Why does a dull hypodermic needle hurt more than a sharp one?

Short Answer

Expert verified

A dull hypodermic needle has more surface area than a sharp needle so more force need to be applied.

Step by step solution

01

Finding difference between dull hypodermic needle and sharp needle

The surface area of a sharp needle is small compared to that of a dull hypodermic needle. Since pressure is the force applied per unit area, pressure will be more acute because of this, as pressure and area are inversely related.

02

Explaining the reason behind the larger pain caused by dull hypodermic needle

Inserting a dull needle is more painful than inserting a sharp one. Because pressure will be less in a dull needle, more force will have to be applied to puncture the skin. In the case of a sharp needle, it will puncture easily.

So, the larger surface area of a dull hypodermic needle hurts more than a sharper needle.

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Most popular questions from this chapter

Assuming bicycle tires are perfectly flexible and support the weight of bicycle and rider by pressure alone, calculate the total area of the tires in contact with the ground. The bicycle plus rider has a mass of80.0kg, and the gauge pressure in the tires is3.50×105Pa.

You can chew through very tough objects with your incisors because they exert a large force on the small area of a pointed tooth. What pressure in Pascal can you create by exerting a force of \[{\rm{500 N}}\] with your tooth on an area of \[{\rm{1}}{\rm{.00 m}}{{\rm{m}}^{\rm{2}}}\]?

Figure shows a glass of ice water filled to the brim. Will the water overflow when the ice melts? Explain your answer.

Consider a group of people trying to stay afloat after their boat strikes a log in a lake. Construct a problem in which you calculate the number of people that can cling to the log and keep their heads out of the water. Among the variables to be considered are the size and density of the log, and what is needed to keep a person’s head and arms above water without swimming or treading water.

A negative pressure of 25.0 atm can sometimes be achieved with the device in Figure 11.44 before the water separates. (a) To what height could such a negative gauge pressure raise water? (b) How much would a steel wire of the same diameter and length as this capillary stretch if suspended from above?
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