1. Simple Machines As well as Work Efficiency and Mechanical advantage

2. What is a machine? A machine may be thought of as a device that makes work easier.

3. How do machines make work easier? Machines make work easier by: multiplying the size of the force you exert (such as in this pulley system).

4. Machines also make work easier by: changing the direction of that force (such as in the gear, roller & rope assembly in these mini-blinds)

5. A pulley lifting a mass or a pulley on a flagpole.

6. A machine can also do both: multiplying the amount of the force, as well as changing the direction of the force. (such as this pry bar)

7. Other things machines do: Machines transfer force from one place to another. Example: A bicycle chain transfers force to the pedals. belt driven chain driven feet driven

8. Machines can convert energy from one form to another. Example: This electric generator converts chemical energy (gasoline) to mechanical energy to electrical energy. – Not a simple machine.

9. Machines can multiply speed or distance. During one revolution of the bicycle’s pedals, the rim of the wheel travels faster than the pedals.

10. What are simple machines? A Simple Machine is a device that does work with one movement.

12. When you use a pry bar to remove a lid, you are working against friction----the friction between the nails in the lid and the crate.

13. When using a simple machine, you are trying to move something that resists being moved.

14. Applying Force & Doing Work Two forces are involved when a machine is used to do work. First: Effort force (F e ) – the force applied to the machine

15. Second: Resistance force (F r ) –the force applied by the machine to overcome resistance.

16. The pry bar is used to multiply the effort force and open the crate. However, to gain force the effort must push through a greater effort distance than the resistance distance.

17. Law of Work and the Ideal Machine In an “Ideal Machine” is frictionless --- therefore there is no energy loss from friction and heat. For an ideal machine, the work input is equal to the work output. This is called the “Law of Work.”

18. Ideal Machines Equation

19. So in order that work input equals work output, the effort force must travel a greater distance than the resistance force.

22. Law of Work Calculation -Ideal Machines A 500 N barrel is rolled up a 4.00 m ramp to a platform 1.20m above the ground. What force must be applied to the barrel.

23. How much force would be used to lift the barrel to then platform without a ramp? Since the barrel has a weight of 500 N, the effort force required to lift the barrel would be 500N. The work done on the barrel would be W = Fd (500N x 1.20m = 600N). 500 N Effort = 112 lbs 150 N Effort = 34 lbs

24. THE MECHANICAL ADVANTAGE: The Number of times a machine multiplies the effort force is the Mechanical Advantage (MA) of the machine.

25. Mechanical Advantage Calculation – for Ideal Machines For the barrel-ramp problem: The ramp, therefore multiplies the effort put in to moving the barrel to the platform over three times.

26. What about a less than ideal machine? In the real world, friction acts against a machine’s work output, whether it is a pulley system or a ramp. The less friction the more efficient the machine, and the greater the work output.

27. Machine Efficiency Calculation

28. Sample Calculation A sofa weighing 1500 N must be placed in a truck bed 1.0 m off the ground. A mover uses a force of 500 N to push the sofa up an inclined plane that has a slope length of 4.0m. What is the efficiency of this inclined plane?