16-­‐10-­‐28 Machines: Making the World a Be;er Place Lesson 11 FuncMons 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 FuncMons of Machines (conMnued) 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-­‐28 Your Turn •  Take jot notes from pp113-­‐115; p131 –  Not collected, but know this informaMon for the unit test) •  Use the informaMon from pp116-­‐119 to answer the following quesMons: 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 mulMplies 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 mulMplied 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 direcMon 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 fricMonless machines, and is calculated by dividing the input distance by the output distance: IMA = din/dout 2 16-­‐10-­‐28 Ideal Mechanical Advantage When the output distance is greater than the input distance, e.g., a hockey sMck that sends a puck very far with relaMvely limited player movement, the ideal mechanical advantage is less than 1. In these situaMons, 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 Simple Machines: (1) The Lever –  Not collected, but use it to conMnue preparing for the unit test •  Use pp116-­‐118 to answer quesMons 1-­‐3 on p119 and quesMons 2-­‐8 on p122 •  Complete the worksheet on mechanical advantage Lesson 13 Classes of Levers The Lever A lever is a rigid bar supported at one point, called the fulcrum. The locaMon of the fulcrum, input force, and output force differ depending on the type, or class, of lever. Also, the input and output forces may act in the same or in opposite direcMons, depending on the class of lever. Class of Lever Fulcrum Loca6on Between input and output forces Second At opposite end of input force; output force between them Third* At opposite end of output force; input force between them First Direc6on of Input and Output Forces Opposite Same Same Example Prying open a paint can Using a bo;le opener ShooMng a puck with a hockey sMck *Mechanical advantage is <1, since the output force is less than the input force. However, output speed is greater than input speed. 3 16-­‐10-­‐28 Classes of Levers Class of Lever Fulcrum Loca6on Between input and output forces Second At opposite end of input force; output force between them Third* At opposite end of output force; input force between them First Direc6on of Input and Output Forces Opposite Same Same Classes of Levers Example Prying open a paint can Using a bo;le opener ShooMng a puck with a hockey sMck *Mechanical advantage is <1, since the output force is Class of Lever Between input and output forces Second At opposite end of input force; output force between them Third* At opposite end of output force; input force between them First Between input and output forces Second At opposite end of input force; output force between them Third* At opposite end of output force; input force between them First Direc6on of Input and Output Forces Opposite Same Same Same Same Example Prying open a paint can Using a bo;le opener ShooMng a puck with a hockey sMck less than the input force. However, output speed is greater than input speed. Classes of Levers Fulcrum Loca6on Direc6on of Input and Output Forces Opposite *Mechanical advantage is <1, since the output force is less than the input force. However, output speed is greater than input speed. Class of Lever Fulcrum Loca6on The IMA of Levers Example Prying open a paint can Using a bo;le opener ShooMng a puck with a hockey sMck *Mechanical advantage is <1, since the output force is less than the input force. However, output speed is greater than input speed. An Example What class of lever is shown? What is the IMA of the wheelbarrow? The IMA of all levers is calculated by dividing the length of the input arm by the length of the output arm: IMA = Lin/Lout •  The length of the input arm is the distance between the input force and the fulcrum •  The length of the output arm is the distance between the output force and the fulcrum Your Turn •  Take jot notes from pp132-­‐135 –  Not collected, but use it to prepare for the unit test •  Use pp132-­‐135 to answer quesMons 3-­‐4, 7-­‐8, 13 on pp152-­‐153 –  For ques#on 13, include a diagram that clearly shows the class of the lever to support your calcula#on •  Read p141 and have tables 5.1 and 5.2 copied out à We will do this lab next class! 4