1.introduction
- 2. Definition Pressure – Force – Area relationship Pascal’s Law Hydraulic Press Hydraulic Brake Conservation of Energy
- 3. It deals with the transmission of force in a confined area It works on the principle discovered by French scientist named Blaise Pascal
- 4. Pressure is the force acting on unit area it is usually expressed in pound per square inch (PSI) or Newton per square meter (Pascal)
- 6. We use the Pressure–Force–Area triangle to find relationship between them P
- 7. We use the Pressure–Force–Area triangle to find relationship between them A
- 8. We use the Pressure–Force–Area triangle to find relationship between them F
- 9. Force: Pound / Newton Area: in2 / m2 Pressure: Pound per square inch (PSI) / Newton per square meter (Pascal)
- 10. Pressure applied on confined fluid is transmitted in all directions and acts with equal force on equal area and at right angle (90 degree) to them. This is the basic principle behind all hydraulic systems Simply, force applied at any point can be transmitted to another point using incompressible liquid
- 11. Take a glass bottle filled with fluid. A small input force is applied to stopper Pressure equal to force divided by stopper area is created in the fluid In this cause it is 10 lb per sq inch According to this law this developed pressure will travel through liquid in all direction This pressure acts against equal area of bottle The resultant output force is multiplied by the bottom area of bottle
- 12. Area of bottom of bottle is 20 in2 So in this case output of 200 lb force is generated with input force of 10 lb. Due to this increase in force the bottle brakes Remember as a simple rule of thumb, In Hydraulics a small force on a small area creates a proportionately large force on a large area
- 13. What would be the pressure developed if a force of 50 lb acts on area of 10 square inches. 500 PSI 50 PSI 5 PSI Its 50 X 10 = 500 PSI
- 14. Hydraulic press uses the principle stated by Pascal’s law We can multiply the force on small area to the force on larger area Hydraulic press also called Bramah press after the inventor Joseph Bramah of England invented it in 1795 . A force of 10 lb is applied to a piston of 1 in2. Resultant system pressure on smaller piston is 10 PSI This pressure is transmitted undiminished (not reduced) through the fluid till it acts on big cylinder with area of 10 in2.
- 15. So resultant force on large piston is (pressure X area) 10 PSI X 10 in2 = 100 lb This force balances the downward force of 100 lb due to weight of the cylinder
- 16. A small force is applied on brake pedal whose area is small The pedal transmits the resultant pressure through the hydraulic oil Force gets multiplied on the brake piston which has a larger area
- 17. The of conservation of energy states “ Energy can neither be created nor destroyed”. The multiplication of force in hydraulics gives the impression that energy is being created, because of force multiplication. This is not the case however As energy is measured in terms of ‘amount of work done’ And, work is defined as Work = Force X Distance In the previous example force on small piston is sufficient to move large piston
- 18. However it must be noted that smaller piston moves 10 inches to move large piston 1 inch If the smaler piston moves by 10 inch inside container, the volume of fluid displaced is calculated as Volume = Piston area X Distance = 1 in2 X 10 in = 10 in3 Hence the amount of work accomplished or force over a distance is same for both the pistons This proves the energy is not created though force is multiplied
- 19. The volume displaced by fluid pushes the larger piston, the distance by which the larger piston moves is calculated as Distance = Volume / Piston area = 10 in3 / 10 in2 = 1 inch The distance each piston moved is inversely proportional to area From this we conclude “what is gained in force is scarified in distance”