Chapter 3 : Pressure and builds static

Pressure

A normal force exerted by a fluid per unit area

Absolute pressure

• The actual pressure at a given position. It is measured relative to absolute vacuum (i.e., absolute zero pressure).

• Tekanan sebenar pada sesuatu kedudukan. Ia diukur berbanding vakum mutlak (iaitu tekanan sifar mutlak).

Gage pressure

• Called gauge pressure

• Difference between absolute pressure and atmospheric pressure

• Measured relative to local atmospheric pressure

• Most pressure gauges are calibrated to zero in air

• Can be positive or negative

• Dipanggil tekanan tolok (gauge pressure)

• Perbezaan antara tekanan mutlak dan tekanan atmosfera

• Diukur berbanding tekanan atmosfera setempat

• Kebanyakan alat pengukur tekanan ditetapkan sifar dalam udara

• Boleh jadi positif atau negatif

Vacuum pressures

Pressures below atmospheric pressure.

Variation of Pressure with Dept

The pressure is the same at all points on a horizontal plane in a given fluid regardless of geometry, provided that the points are interconnected by the same fluid.

Pascal’s law

The pressure applied to a confined fluid increases the pressure throughout by the same amount.

The area ratio A2 /A1 is called the ideal mechanical advantage of the hydraulic lift.

Pascal’s Paradox

• The size of the small volume of fluid does not affect the result.

• The change in pressure depends only on the change in elevation and the type of fluid, not on the size of the fluid container.

• All containers in the figure below contain vastly different amounts of fluid, but they would have the same pressure at the bottom.

• This observation is called Pascal’s paradox.

• Dikenali sebagai Paradox Pascal (Pascal’s paradox)

• Saiz isipadu kecil bendalir tidak mempengaruhi keputusan tekanan

• Perubahan tekanan hanya bergantung pada perubahan ketinggian dan jenis bendalir

• Tidak bergantung pada saiz bekas atau jumlah bendalir

• Bekas berbeza boleh memberi tekanan yang sama pada dasar jika tinggi bendalir sama

The Barometer

• Atmospheric pressure is measured using a barometer

• Also known as barometric pressure

• Standard unit is 1 atmosphere (atm)

• Defined using a 760 mm column of mercury at 0°C

• Depends on mercury density and standard gravity

The Manometer

It is commonly used to measure small and moderate pressure differences. A manometer contains one or more fluids such as mercury, water, alcohol, or oil.