Chapter 2.1.2 Work in Mechanical Systems

1. Chapter 2.1.2Work in Mechanical Systems Principles of Technology I Edinburg North High School

2. Notes 2.1.1Work in Mechanical Systems Objectives: • Identify basic machines. • For a given machine, identify the input and output work. • Explain how efficiency relates to input and output work for a mechanical system. • Calculate efficiency for non-ideal (real machines)

3. Machines • Machines can make work easier by: • changing the direction of the force used to do the work; • and multiplying the force used to do the work. • In an ideal machine, the work put into the machine is equal to the work coming out of the machine.

4. An Inclined Plane (or Ramp)

5. Mechanical Advantage • Mechanical Advantage (MA) is the number of times the output force is multiplied by a machine. • If in an ideal machine • then • By definition of MA

7. Six Types of Machine in Two Families

8. Real Machines Are Not 100% Efficient • Machines are designed to convert input work into useful forms of energy or output work. • In real machines the output work is always less than the input work. • Some input work has to overcome undesired loses such as the negative work of friction. • Machines are often rated by efficiency or percent efficiency. • Efficiency in real machines is always less than 1, or 100%

10. Sample Problem • A sailor uses a rope and an old, squeaky pulley to raise a sail that weighs 140 N. He finds that he must do 180 J of work on the rope in order to raise the sail by 1 m (doing 140 J of work on the sail). What is the efficiency of the pulley? Express your answer as a percentage.

11. Example 2.3 Work and Efficiency for a Block and Tackle, p. 89 • The block and tackle shown in figure 2.3 (p. 88) is used to lift an automobile engine. The engine weighs 600 lb and is raised 0.9 ft. The operator pulls with a force of 100 lb over a distance of 6 ft. Calculate the efficiency of the block and tackle system.