Calculate the average force per nail when Sara, who weighs 120 pounds, lies on a bed of nails and is supported by 600 nails.

What geometrical shape has the smallest surface area for a given volume?

How does the height to which water is lifted in a capillary tube relate to adhesion and the weight of the water lifted?

The top floor of a building is $20 \mathrm{~m}$ above the basement. Show that the water pressure in the basement is nearly $200 \mathrm{kPa}$ greater than the water pressure on the top floor.

The depth of water behind the Hoover Dam is $220 \mathrm{~m}$. Show that the water pressure at the base of this dam is $2200 \mathrm{kPa}$

Show that the water pressure at the bottom of the 50 -m-high water tower in the chapter-opening photo is $500,000 \mathrm{~N} / \mathrm{m}^2$, which is approximately $500 \mathrm{kPa}$

A $1 \mathrm{~m}$ tall barrel is filled with water (with a weight density of $\left.10,000 \mathrm{~N} / \mathrm{m}^3\right)$. Show that the water pressure on the bottom of the barrel is $10,000 \mathrm{~N} / \mathrm{m}^2$ or, equivalently, $10 \mathrm{~kPa}$.

Calculate, in $\mathrm{kPa}$, the pressure exerted by a column of water that is $10-\mathrm{m}$ tall. Assume the weight density of water to be $10,000 \mathrm{~N} / \mathrm{m}^3$, and ignore the pressure due to the atmosphere.

Calculate the pressure a $2-\mathrm{N}$ book exerts on the table it rests on if its area of contact is $50 \mathrm{~cm}^2$.

$$\text { Pressure }=\text { weight density } \times \text { depth }$$

(Use $10,000 \mathrm{~N} / \mathrm{m}^3$ for the weight density of water, and ignore the pressure due to the atmosphere in the calculations below.)

Calculate the pressure a $10 \mathrm{~N}$ block exerts on the table it rests on if its area of contact is $50 \mathrm{~cm}^2$.

Pressure $=$ weight density $\times$ depth

(Use $10,000 \mathrm{~N} / \mathrm{m}^3$ for the weight density of water, and ignore the pressure due to the atmosphere in the calculations below.)

What is the relationship between liquid pressure and the depth of a liquid? Between liquid pressure and weight density?

What is meant by weight density? How does the pressure exerted by a column of water depend upon weight density?

Float a water-soaked Ping-Pong ball in a can of water held more than a meter above a rigid floor. Then drop the can. Careful inspection will show that the ball was pulled beneath the surface as both the ball and the can drop. What does this say about surface tension? More dramatically, when the can makes impact with the floor, what happens to the ball, and why? Try it and you'll be astonished! (Caution: Unless you're wearing safety goggles, keep your head away from above the can when it makes impact.)

If you punch a couple of holes in the bottom of a water-filled container, water will spurt out because of water pressure. Now drop the container, and, as it freely falls, note that the water no longer spurts out! Explain.