### Theory:

Before getting to know the solid body pressure let us solve a problem.

**Who puts more pressure on the surface - an elephant or a girl in high heels?**

The elephant weighs 4000 kg | The girl weighs 50 kg |

The answer to this question can be surprising.

The amount of pressure does not depend only on body weight!

Pressure is a physical quantity that describes how much force is applied to a unit of surface area perpendicular to the surface.

SI unit of pressure is measured in newtons per square meter, or pascals $1\mathit{Pa}=1\frac{N}{{m}^{2}}$ $\mathit{pressure}=\frac{\mathit{pressure}\phantom{\rule{0.147em}{0ex}}\mathit{force}}{\mathit{Square}\phantom{\rule{0.147em}{0ex}}\mathit{area}}\phantom{\rule{0.147em}{0ex}}\phantom{\rule{0.147em}{0ex}}\phantom{\rule{0.147em}{0ex}}\phantom{\rule{0.147em}{0ex}}\phantom{\rule{0.147em}{0ex}}\phantom{\rule{0.147em}{0ex}}\phantom{\rule{0.147em}{0ex}}p=\frac{F}{S}$

A force acting on a body perpendicular to its surface is called a compressive force.

Often in exercises, the force of pressure is equal to the weight of the body.

Often in exercises, the force of pressure is equal to the weight of the body.

With the same pressure force, it is possible to obtain pressures of different magnitudes, because it depends on the dimensions of the support area, the smaller the area, the higher the pressure.

The unit of pressure is Pa (pascals).

1 Pa is low pressure. So use,

1 Pa is low pressure. So use,

hectopascals 1 hPa = 100 Pa;

kilopascals 1 kPa = 1000 Pa;

megapascals 1MPa = 1000,000 Pa;

gigapascals 1GPa = 1000 000 000 Pa.

Let's solve the problem about the elephant and the girl.

To determine the pressure, you still need to know the size of the support area.

The elephant's foot is about 200 ${\mathit{cm}}^{2}$, as the elephant stands on four legs, this figure must be multiplied by 4.

The area of the ladies' shoe that is in contact with the support area is approximately 10 ${\mathit{cm}}^{2}$ (Look at the picture, the girl stands on one leg).

The force pushing on the support area, in this case, is the weight of both bodies.

$\begin{array}{l}{m}_{z}=4000\mathit{kg}\\ {S}_{z}=800{\mathit{cm}}^{2}\\ {m}_{m}=50\mathit{kg}\\ {S}_{m}=10{\mathit{cm}}^{2}\\ g\approx 10m/{s}^{2}\\ \_\_\_\_\_\_\_\_\_\_\_\\ \mathit{Compare}\phantom{\rule{0.147em}{0ex}}\phantom{\rule{0.147em}{0ex}}p\end{array}$ | $\begin{array}{l}\\ =0,08{m}^{2}\\ \\ =0,001{m}^{2}\end{array}$ | $\begin{array}{l}\phantom{\rule{0.147em}{0ex}}p=\frac{F}{S}\\ \\ F=P=\mathit{mg}\end{array}$ | $\begin{array}{l}{p}_{z}=\frac{4000\cdot 10}{0,08}=\mathit{500000}\phantom{\rule{0.147em}{0ex}}\left(\mathit{Pa}\right)\\ {p}_{m}=\frac{50\cdot 10}{0,001}=\mathit{500000}\phantom{\rule{0.147em}{0ex}}\left(\mathit{Pa}\right)\end{array}$ |

**Answer:**The elephant and the girl put equal pressure on the support.

Reference:

Fizika 9. klasei. Ilgonis Vilks./ ZvaigzneABC-2008. izm.36.lpp.