Vacuum cleaners take up dust from the floor with the help of external air pressure.
When the pressure in front of the motor drops, that is, a partial vacuum is created, suction occurs: the external air flows into the vacuum cleaner because the air pressure inside the vacuum cleaner is lower than the pressure outside. Together with the air, dust also flows into the inside of the vacuum cleaner.
Air pressure inside the vacuum cleaner
normal atmospheric pressure
3,000 Pa – 0.1 Pa
10 Pa – 1 Pa
The word vacuum means 'empty space' in Latin, that is, space where there is nothing: no air, nor any other particles. It does not occur in nature, a perfect vacuum does not exist. We usually use this term to refer to a partial vacuum, a space where gas pressure is very low. In vacuum cleaners there is no perfect vacuum either, indeed, there is only a relatively weak vacuum.
Syringes act like pumps, their operation is based on creating a weak vacuum. By pulling the plunger up in the syringe, we increase the internal volume, which results in a decrease in pressure. The external, higher-pressure air pushes the fluid that we want to take into the syringe.
pressure of the liquid column
Evangelista Torricelli(1608-1647) was the first to recognise the role of atmospheric pressure in the use of suction pumps.
He also discovered that at normal atmospheric pressure a pump cannot hold a liquid column of unlimited height, 10 metres was the limit. During his experiments with mercury, he found that at normal athmospheric pressure the maximum height of a column of mercury in a tube was 760 mm. Since mercury is about 13 times denser than water, this was equivalent to a column of water of about 10 m in height.
Atmospheric pressure results from the weight of the air column above us at the point of measurement. Normal atmospheric pressure is measured at sea level. As elevation increases, there is less overlying air, so atmospheric pressure decreases.