P14. Pressure
Physics of pressure chapter | |
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Example Calculations
A force of 20 N acted over an area of 2 m2 (two square metres). What is the pressure?
force ÷ area = pressure
20 ÷ 2 = 10 N/m2
force ÷ area = pressure
20 ÷ 2 = 10 N/m2
Air Pressure
There is also an immense amount of weight pressing down on you from all of the air above you. If we measured all of the air starting with the air that is resting on your shoulders up to the top of the atmosphere, we will find that you have around 1000 kg of air pressing down on your body! This is the same mass as a small car! We don’t notice this incredible pressure on our bodies because our bodies are meant to function in this pressure. |
Pressure in liquids
Hydraulics
Particles in liquids are close together, making liquids virtually incompressible. As the particles move around, they collide with other particles and with the walls of the container. The pressure in a liquid is transmitted equally in all directions,so a force exerted at one point on a liquid will be transmitted to other points in the liquid.
Pressure can be transmitted through liquids. In hydraulic machines, exerting a small force over a small cross-sectional area can lead to pressure being transmitted, creating a large force over a large cross-sectional area. This ability to multiply the size of forces allows hydraulics to be used in many applications such as car-braking systems.
Car Brakes
We can use pressure in liquids to move a piston and do useful work. This is how the hydraulic systems in diggers, car brakes and fairground rides work: a pump creates pressure in an incompressible liquid, which acts on a piston. By adjusting the area of the piston, we can adjust the force we get.
Hydraulics Practical
pressure_and_force-hydraulic.pdf | |
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The pressure in a liquid is equally transmitted in all directions. This means that when a force is applied to one point of the liquid, it will be transmitted to other points within the liquid. This principle can be exploited in hydraulic machines. Imagine that two syringes of different sizes were connected by tubing and filled with water. An effort force exerted on the plunger for syringe A puts greater pressure on the water in tube A. As water is virtually incompressible, the pressure is transmitted through the water into syringe B. The water pushes against the plunger in syringe B with equal pressure, exerting a load force on it.However, tube B has a plunger with a bigger cross-sectional area than tube A. This means that the load force exerted is larger than the effort force exerted. This is known as a force multiplier
Hydraulic systems therefore allow smaller forces to be multiplied into bigger forces. Note, however, that the bigger syringe moves a shorter distance than the smaller syringe.
Hydraulic systems therefore allow smaller forces to be multiplied into bigger forces. Note, however, that the bigger syringe moves a shorter distance than the smaller syringe.