1.4 PRESSURE. 1.4.1 Pressure in a fluid 1.4.2 The effect of gravity on pressure 1.4.3 The effect of gas temperature on pressure 1.4.4 Propagation of waves 1.4.5 Attenuation of waves. Pressure = Force / Area. Force F 1 Area A 1. Force F 2 Area A 2. F 2 = F 1 A 2 /A 1. Piston.
Force F1 Area A1
Force F2 Area A2
F2 = F1 A2/A1
The pressure at a depth h metres below an open surface of a liquid is given by:
where is the density (1000 kg/m3 for water) and g is 9.81 m/s2.
= 1 Bar
= 100 kPa (kilo Pascal)
= 0.1 N/mm2
= 10 m water head
Pressure in mm of mercury
Approx 1 m.
Would be 10 m for water
There is an approximate equation which may be used to calculate the change in pressure in a gas when it is heated. The "ideal gas equation" is:
P1, V1, and T1 are the pressure, volume and temperature before the change and P2 etc. are the values for after the change. Note that T must be in Kelvin, not centigrade.
L1Schematic diagram of movement of an element of a solid
The force on the weight will cause it to accelerate: F=ma
F is the force = stress area
m is the mass = Al1
and a is the acceleration
Thus: F = EyA/l2
The solution to this "simple harmonic motion"
Movement of a wave. Pressures at time T and T+T. The velocity of the wave is the frequency the wavelength
We define the bulk modulus B as follows: