It rests upon the edge of the cup. [Illustration: Fig. 40.] What is the cup on which the spoon rests called? It is called a _Fulcrum_. What is a fulcrum? A fulcrum is any solid body against which a lever rests. When the spoon is called a lever, what are the parts on each side of the fulcrum called? They are called the _arms_ of the lever. What is necessary, so that a lever may balance? The arms of the lever must be of equal weight, or they will not balance. If the bowl of the spoon be filled with water, what will result? The bowl will sink, and the handle of the spoon will rise. What will cause the bowl of the spoon to sink? The weight of the water in it will cause it to sink. How can the bowl of the spoon be prevented from sinking? By applying a force to the handle of the spoon, equal to the weight of the water put in the bowl. What is the force applied to the handle called? It is called the _Power_. What three things are always necessary when the lever is used? The power, the _fulcrum_, and the _weight_, are always necessary when the lever is used. Which of these three things are movable? The power and the weight are movable. Which one does not move? The fulcrum does not move. How many kinds of levers are there? There are three kinds of levers. What is the first kind of lever? It is where the fulcrum is between the power and the weight, as is shown in Fig. 41. [Illustration: Fig. 41.] When the fulcrum is under the middle of the lever, how can the lever be kept balanced? The lever will remain balanced, so long as the power and the weight used are equal to each other. When the lever is moved, so that the fulcrum is nearer the weight, which arm of the lever is the heavier? The arm towards the power, because it is the longer arm. Will the power applied to the long arm of the lever be as heavy as the weight? No; the nearer the fulcrum is to the weight, the less will be the power needed to balance that weight. How will it be when the fulcrum is nearer to the power than it is to the weight? Then the power must be heavier than the weight. When the long arm of the lever is twice the length of the short arm, what will be the difference in the weights? One pound applied to the long arm will then balance two pounds applied to the short arm. Upon what does the power of a lever depend? It depends upon how much nearer the fulcrum is placed to one end of the lever, than to the other end. Of what use is the lever? It is very useful in raising heavy bodies. [Illustration: Fig. 42.] What is the weight to be lifted in Fig. 42? The stone is the weight to be lifted. Where is the fulcrum placed? The fulcrum is placed near the stone. Where is the power applied? The power is applied by the hand to the long arm of the lever. How may a see-saw be made? A see-saw may be made by placing a plank or a board across a rail in a fence, so that it will balance.