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A crowbar lets one person lift a stone that ten could not lift by hand. A ramp lets a barrel go up to a truck bed that nobody could raise straight up. A pair of tongs, oddly, makes the job harder rather than easier — and is still a machine.
All of that is one idea. A machine does not create energy and cannot give you something for nothing. What it does is trade one quantity against another: it multiplies your force and makes you move a longer distance, or it multiplies your speed and range and makes you push harder.
That trade is why the tongs belong on the list. They cost you force and buy you delicacy and reach, which is exactly what picking up a hot coal needs.
This chapter has only six devices, three lever classes and about four formulas, and the questions rotate among them year after year. Once you can locate the fulcrum in a picture and write one ratio, the whole topic becomes arithmetic.
1. A wheelbarrow is an example of which class of lever?
2. In a third-class lever, the mechanical advantage is:
3. The ideal mechanical advantage of a single fixed pulley is:
4. The mechanical advantage of an inclined plane is given by:
5. A lever has an effort arm of 100 cm and a load arm of 20 cm. Its ideal mechanical advantage is:
6. Which of the following is a first-class lever?
7. The efficiency of any real machine is:
8. A crowbar is used so that a small effort lifts a heavy stone. This necessarily means that the effort must move: