16-­‐10-­‐22 Machines: Making the World a Be:er Place Lesson 11 FuncLons of Machines A machine is any mechanical system that reduces the force required to accomplish work. Machines make work easier by: 1.  Increasing the force that can be applied to an object, e.g., when using a nutcracker, your hands apply a smaller force over a larger distance, allowing the nutcracker to apply a larger force over a smaller distance, since W = Fd 2.  Increasing the distance over which a force is applied, e.g., the longer the ramp, the less force is required to accomplish the same amount of work, since W = Fd 3.  Changing the direc6on of the force, e.g., a pulley on a flagpole FuncLons of Machines (conLnued) The force applied to a machine is called the input, or effort, force (Fin), while the force a machine applies to an object, or the force required to move the object without a machine, is called the output, or load, force (Fout). Simple Machines All machines, no ma:er how complex, are made up of at least one of the six simple machines. Rube Goldberg Machine – a comically involved,
complicated invention, laboriously contrived to
perform a simple operation
(Webster’s New World Dictionary)
1 16-­‐10-­‐22 Your Turn •  Take jot notes from pp113-­‐115; p131 –  Not collected, but know this informaLon for the unit test) •  Use the informaLon from pp116-­‐119 to answer the following quesLons: 1. 
2. 
3. 
4. 
What is mechanical advantage? What does a mechanical advantage of 1 mean? What is ideal mechanical advantage? Why is it only possible to calculate, not create, a machine’s ideal mechanical advantage? 5.  What does an ideal mechanical advantage of less than 1 mean? Mechanical Advantage In a Perfect World: Mechanical Advantage and Ideal Mechanical Advantage Lesson 12 Mechanical advantage describes the amount by which a machine mulLplies an input force to produce an output force. For example, if a person pushes down on a car jack with a force of 250N, and the jack raises a 3000N car, the jack has mulLplied the input force by 12, since 3000/250 = 12. Thus, the mechanical advantage of the jack is 12. Mechanical Advantage Mechanical advantage is calculated by dividing the output force by the input force: MA = Fout/Fin When a machine does not change the size of an input force, e.g., a pulley that changes the direcLon of a force, its mechanical advantage is 1. Ideal Mechanical Advantage Ideally, the en#re input force is used to produce the output force. However, fric6on converts some of the input force into thermal energy, which takes away from the output force. Though impossible, ideal mechanical advantage is the mechanical advantage of fricLonless machines, and is calculated by dividing the input distance by the output distance: IMA = din/dout 2 16-­‐10-­‐22 Ideal Mechanical Advantage When the output distance is greater than the input distance, e.g., a hockey sLck that sends a puck very far with relaLvely limited player movement, the ideal mechanical advantage is less than 1. In these situaLons, the speed at the output force also tends to be much greater than the speed at the input force. Upcoming In the next few classes, we will be looking more closely at the six simple machines, and at how to calculate their ideal mechanical advantages. Next class: Levers and Pulleys Your Turn •  Take jot notes from pp116-­‐119 –  Not collected, but use it to conLnue preparing for the unit test •  Use pp116-­‐118 to answer quesLons 1-­‐3 on p119 and quesLons 2-­‐8 on p122 •  Complete the worksheet on mechanical advantage 3