# Atmospheric Pressure on Shaft of piston cylinder assembly

• dkjjjj0302
In summary, the problem involves determining the magnitude of force required on a vertical shaft attached to a piston in a cylinder, given the gas pressure, piston and shaft masses, and atmospheric pressure. The force required is calculated using the equilibrium force balance, taking into account the area of the piston and the atmospheric pressure acting on it.
dkjjjj0302

## Homework Statement

In a vertical piston cylinder assembly, a vertical shaft whose cross sectional area is 0.8 cm^2 is attached to the top of the piston. Determine the magnitude F, of the force acting on the shaft, in N, required if the gas pressure inside the cylinder is 3 bar. The masses of the piston and attached shaft are 24.5 and 0.5 kg respectively. The piston diameter is 10 cm. The local atmospheric pressure is 1 bar. The piston moves smoothly in the cylinder and g=9.8 m/s^2

P=F/A

## The Attempt at a Solution

I converted the atmospheric pressure and gas pressure to forces. I summed all the forces acting on the cylinder. F= -Wshaft - Wpiston + Fgas -Fatm -F=0 Now my problem is, when I find the force caused by atmospheric pressure, do I subtract the area of the shaft from the area of the piston >> Fatm = Pressure (Area(piston)-Area(shaft)) ? How does atmospheric pressure not act on the top of the shaft, shouldn't Fatm = Pressure(Area(piston))?

dkjjjj0302 said:
How does atmospheric pressure not act on the top of the shaft, shouldn't Fatm = Pressure(Area(piston))?

If there is no seal or other pressure controlling feature at the top of the shaft then atmospheric pressure acts on the shaft end in the normal way .

Area to be used for calculating atmospheric pressure force is effectively just the total area of the piston - the hatched area shown in diagram below .

Last edited:

You should be considering the equilibrium force balance on the combined piston and shaft, not the cylinder.

## 1. What is atmospheric pressure?

Atmospheric pressure is the force per unit area exerted by the weight of the Earth's atmosphere. It is caused by the weight of the air above a certain point and is measured in units of pressure such as pounds per square inch (psi) or pascals (Pa).

## 2. How does atmospheric pressure affect the shaft of a piston cylinder assembly?

Atmospheric pressure plays a crucial role in the operation of a piston cylinder assembly. It exerts a force on the piston, which is then transferred to the shaft. The amount of force depends on the area of the piston and the atmospheric pressure. This force can affect the movement and performance of the shaft.

## 3. Can atmospheric pressure cause damage to the shaft of a piston cylinder assembly?

Yes, atmospheric pressure can cause damage to the shaft of a piston cylinder assembly if it is too high or too low. High atmospheric pressure can put excessive stress on the shaft, leading to deformation or failure. Low atmospheric pressure can cause the shaft to expand, resulting in misalignment or leakage in the assembly.

## 4. How can we measure atmospheric pressure on the shaft of a piston cylinder assembly?

There are various instruments that can be used to measure atmospheric pressure, such as barometers, manometers, and pressure gauges. These instruments can be attached to the shaft of the piston cylinder assembly to measure the force exerted on it by atmospheric pressure.

## 5. How does temperature affect atmospheric pressure on the shaft of a piston cylinder assembly?

Temperature has a direct effect on atmospheric pressure. As temperature increases, the air molecules in the atmosphere gain more energy and move around more, resulting in an increase in atmospheric pressure. This can cause the shaft of a piston cylinder assembly to experience more force from the atmosphere, which can affect its performance and durability.

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