Unit 4

1. Unit 4 Mechanical Systems

2. Unit 4 Topic 2.2 - Work

3. Work • So what is “work” • Work is done when a force acts on an object to make the object move Bat hitsballBat doeswork onball

4. Work Cont … • So here is a scenario … • Is workhappening in this picture?

5. Calculating Work • So to calculate this … • W = Work  N.m (Newton meters) • F = Force  N (Newtons) • D = Distance  m (Meters) • This is your money maker right here W d F

6. Work Marvel at my beard! You are welcome world! • A “Newton meter” is also referred to a Joule • What is a joule? • It was discovered by James Joule

7. Energy & Work • Energy and work are closely related • Back to bikes … • When you push the pedals you exert a force on them • The chain (linkage) transfers the force to the wheels • Your energy is used to provide the force that drives the pedals that move the wheels • Work is being done because the force you apply to the pedals causes the bike to move

8. Work & Machines • Does using a machine mean less work is done? • You use the machine so you do not have to exert as much force • BUT … the same amount of work is being done! • Let us test this theory!

9. Work w Machines • Ok this picture as no point … just funny to me! • Let us use this one … • See Sec 2.2

10. Work & Machines • The work done with a machine is the same as the work done without it • This can be shown by calculating work input and work output

11. Work & Machines • Work input is the work needed to use, or operate, the machine Work input = Force input x d input • Work output is the work done by the machine Work output = Force output x d output Efficiency = Work output x 100 Work input

12. Unit 4 Topic 2.3 Hydraulics

13. Hydraulics • Most machines that move very large, very heavy objects use a hydraulic system that applies force to levers, gears or pulleys • A hydraulic system uses a liquid under pressure to move loads • It is able to increase the mechanical advantageof the levers in the machine

14. Hydraulics • Modern construction projects use hydraulic equipment because the work can be done quicker and safer • There are many practical applications of hydraulic systems that perform tasks, which makes work much easier.

15. Lifts • A hydraulic lift is used to move a car above the ground, so a mechanic can work underneath it.

16. Pressure & Pascals • Pressure is a measure of the amount of force applied to a given area p = F / A p is pressure A is Area F is Force • The unit of measurement for pressure is a pascal (Pa), named after Blaise Pascal who did important research on fluids • 1 Pascal is equal to the force of 1 Newton over an area of 1 m2

17. Pressure & Pascals • Some Key Quick Facts … • 1 Pascal or 1N over an area of 1m2 is a very small amount of force • To counter this we typically use 1 Kilopascal where kilo = 1000 • Also, for smaller forces, we can also use 1 N over 1 cm2

18. Pressure & Pascals • Pascal discovered that pressure applied to an enclosed fluid is transmitted equally in all directions throughout the fluid • This is known as Pascal’s Law and it makes hydraulic (liquid) and pneumatic (air) systems possible • A common application of Pascal’s law is illustrated with the hydraulic jack.

19. Pistons & Pressure • In hydraulic systems, the pressure is created using a piston • Pistons can be different sizes and hydraulic devices use pistons that are different sizes attached to each other with a flexible pipe • The Input Piston is used to apply force to the fluid, which creates pressure in the fluid • The fluid transfers this pressure to the output piston • This pressure exerts a force on the output piston and the result is a mechanical advantage that makes the hydraulic system very useful

20. MA In Hydraulics • The mechanical advantage in a hydraulic system comes from the fluid pressure in the system • Using the input force and the output force will give you the Mechanical Advantage of the system MA = Output force / Input force MA = 500N / 25N MA = 20 • Mechanical advantages in hydraulic systems are usually quite high, showing how useful they are. Fout = 500N Fin = 25N

21. MA & Pressure • The reason for the large mechanical advantage in a hydraulic system is the ability of the fluid to transmit pressure equally • It allows you to use a small force on the small piston to produce a larger force on the large piston p = F / A p = 20N / 4cm2 p = 5N/cm2

22. Pressure & Pascals • From Pascal’s law, we know that the pressure the small piston creates is the same everywhere in the fluid • So the large piston has a larger area and is able to multiply the pressure because of its larger area • The force and area at each piston act as ratios that have to be equal.

23. Force of the small piston Force of the large piston = Area of the small piston Area of the large piston Fout = X? Fin = 20N Ain = 4cm2 Aout = 100cm2

24. Ratios & Pressure • By solving this ratio you will find that the forces created within a hydraulic system provides very • large mechanical advantages - making them useful in many applications.

25. Need More Force? • Mechanical advantage in hydraulic systems has a cost • What would that cost be? • That cost is the increased distance • The smaller force must go through to make the large force move a small distance

26. Robot Fun • Imagine you had to build a robot. You decide, as the genius designers you are, that your robot will have hydraulic arms! The kicker … it needs to help around the house. • Chore-Bot 5000 • What could your robot accomplish with hydraulic arms vs. non-hydraulic arms?