**Pressure** is often confused with force. Pressure is force spread out over an area; a small force exerted on a very small area can create a very large pressure; i.e., poke a pin into your arm!

Key Equations

Pressure is a force exerted over some area

#### Example 1

How much pressure does a 340-g Coke can exert on a table if the diameter of the can is 8.0 cm?

Question:

Given:

Equations: Area of a circle:

Plug n’ Chug:

The answer is 680 Pa.

### Review

- Why does a sharp knife cut so much better than a dull one?
- Every day Fakir likes to spend about an hour meditating on his bed of nails. Fakir’s mass is 60 kg, his bed contains 2000 nails, and each nail point has a surface area of .
- Calculate the total surface area of all the nail points, then convert that area into square meters.
- Calculate the pressure exerted on Fakir by the nails. Compare this to your answer from the previous question.

- Estimate the pressure in Pascals that you exert on the ground when you stand in your bare feet flat compared to 'tippy toes'. Clearly state your assumptions.

**Review (Answers)**

- A sharp knife has much less area of contact, so the pressure is greater (pressure is inversely proportional to area).
- a. b. 75 kPa
- estimates will vary, but expect about a force five times larger for 'tippy toes' due to the smaller area. Discuss in class.