Getting Leverage

Getting Leverage Background: Students should be introduced to the concepts of forces, gravity, and mass. Teachers should have the same background plus an understanding of levers and the relationship between force and the distance from the fulcrum that the force is applied. Abstract: Students will balance various masses on each side of a meterstick. These masses will be at different lengths along the meterstick. The students will then record each mass and it‟s distance from the fulcrum. After all the data is collected, they will attempt to find a relationship between the mass and distance used on one side of the stick compared to the mass and distance used to balance it. Lesson Plan: Goal: Students will use metersticks and masses as an adjustable balance to discover the relationship between forces and the distances they act from the fulcrum as compared to the resulting forces on the other side of the fulcrum. Thus developing an understanding of “leverage.” Content objectives: Knowledge of the properties of levers. Materials: Per group (one meterstick, one 3-4” long dowel stick or a pencil, several blocks (or books), 2 large paperclips, heavy wire (like tying wire), 2 mass hangers and sets of weights) Estimated time: one class period (about 50 minutes) Procedure: Before class attach pieces of dowel rod to the 50cm mark of the metersticks at a 90 degree angle using heavy wire. The idea here is to create an axle for the meterstick to rotate under (not over the axle because it is too unstable). Bend each large paperclip into an „S‟ shape. Instruct the students to place the blocks in two stacks next to each other an inch or two apart. Then place the dowel across the gap between the blocks so that the meterstick swings freely in the gap between the blocks. Two masses will be hung at different distances on each side of the fulcrum by hanging the S-hook paperclips from the meterstick and the mass hangers from the S-hooks. The distances are easy to measure, just use the marks already on the metersticks! Have each group write down different masses and distances in the first two columns and then find masses and distances that will balance them when placed on the other side of the fulcrum (Note that the teacher may have to tell groups not to use only identical sets of numbers for each side; though this will work in every case it is the “trivial” case and need only be done once or twice per group). Then the students will record these masses and distances in the second two columns. Have the students write the proper units for the measurements at the top of each column on the handout. Closure, results and follow through activities: To finish up, ask the students to find a relationship between the masses and distances they used to balance the levers with. Write down on the board and/or have the students write down their ideas on the board and in their science journals. They may not express it this way but some variation or set of conditions should be found that leads to an expression like: mass1 * distance1 = mass2 * distance2 Though not necessarily in this mathematical form, it may be a series of statements of conditions to be met in order to achieve balance. The teacher should lead the class from their conclusions to the above form, not merely state it as a fact. To tie this back to a more “real” application point out that the forces used in many levers are not produced by weight from masses but instead from springs, muscles, and other such sources. Discuss other uses and places of use for levers and why they are used where they are. Standards: PS.1.3, PS.2.6, PS.3.1, PS.3.2, PS.3.4, NPO.2.2 Assessment: In addition to getting an understanding of which students understood the concepts during the class discussion, review the class science journals and check to see if their responses were well thought out. Even if a student is wrong in their details, a logically constructed set of conditions means that the student understood a great deal. Remember when looking through the journals that the entries were preliminary to the discussion and will very likely have errors. The emphasis in reviewing the journals is to determine if the individual student was thinking about the problem in a logical manner before the class discussion took place and the class as a group found the „right‟ answer.