activity Levers for Lifting BROWARD COUNTY ELEMENTARY SCIENCE BENCHMARK PLAN Grade Quarter Activity SC.C... The student understands that the motion of an object can be described and measured. SC.H... The student knows that it is important to keep accurate records and descriptions to provide information and clues on causes of discrepancies in repeated experiments. SC.H... The student knows that a successful method to explore the natural world is to observe and record, and then analyze and communicate the results. SC.H... The student knows that to work collaboratively, all team members should be free to reach, explain, and justify their own individual conclusions. SC.H... The student knows that to compare and contrast observations and results is an essential skill in science. SC.H... The student knows that a model of something is different from the real thing but can be used to learn something about the real thing. SC.H... The student knows that data are collected and interpreted in order to explain an event or concept. ACTIVITY ASSESSMENT OPPORTUNITIES The following suggestions are intended to help identify major concepts covered in the activity that may need extra reinforcement. The goal is to provide opportunities to assess student progress without creating the need for a separate, formal assessment session (or activity) for each of the 0 hands-on activities at this grade level.. Ask, Is it possible for two students on one end of a seesaw to balance with only one student on the other end? (yes) Have them draw a picture of the seesaw labeled as a lever with a fulcrum in the middle of the lever. Ask them to draw Xs where they would place the broward county hands-on science Quarter
two children on one arm and the single student on the other arm so they would balance. (The picture should show the two students very close to the fulcrum on one arm and the single student near or at the end of the other arm.). Use the Activity Sheet(s) to assess student understanding of the major concepts in the activity. In addition to the above assessment suggestions, the questions in bold and tasks that students perform throughout the activity provide opportunities to identify areas that may require additional review before proceeding further with the activity. 8 activity Levers for Lifting
activity Levers for Lifting OBJECTIVES Students are introduced to the first of six types of simple machines: the lever. The students name the parts of a lever use a lever to lift a load discover how the position of the fulcrum affects the amount of force needed to lift the load discuss the tradeoff between force and distance when using a lever to do work SCHEDULE About 0 minutes VOCABULARY arm effort fulcrum lever load pivot simple machine tradeoff MATERIALS For each student Activity Sheet, Parts A and B pr safety goggles* For each team of two fulcrum paint stirrer, wooden pencil* push-pull meter ruler, dual-scale* washers, metal For the class roll tape, masking Delta Science Reader Force and Motion *provided by the teacher PREPARATION Make a copy of Activity Sheet, Parts A and B, for each student. Each team of two will need a push-pull meter, a wooden paint stirrer, metal washers, a fulcrum, a ruler, and pieces of masking tape ( cm long, each). (Replace any push-pull meter rubber bands that have become stretched.) BACKGROUND INFORMATION Unlike complex machines, which have many moving parts and may be powered by gasoline engines or electric motors, a simple machine is a mechanical device that has just one (or no) moving part and requires only manual force from people or animals to perform work. There are six types of simple machines: the lever, wheel and axle, pulley, inclined plane, wedge, and screw. This activity introduces students to the lever. They will learn about the other five simple machines in later activities. A lever consists of a straight bar that rests on and pivots around a support. Applying force to one part of a lever produces a useful action at another part of the lever. Most levers help you do work by reducing the amount of force broward county hands-on science Quarter 9
you need to lift an object or pry something loose, although some levers work by increasing the distance and speed at which you can move an object. Load Effort (force) All levers have four parts: () a rigid bar, called the arm; () the fulcrum, or support around which the arm pivots; () the load, which is the object to be moved; and () the effort, or force that is applied to move the load. Arm Fulcrum There are three types of levers: first-, second-, and third-class levers. One type of lever is not better than another. Each simply has the fulcrum in a different location. In a first-class lever (the subject of this activity), the fulcrum is located between the effort and the load. Pushing down on one end of the lever causes the other end to lift up. In doing so, a first-class lever not only transfers but also changes the direction of the force. Figure - is a diagram of a first-class lever. When the fulcrum is dead-center (as it is in a seesaw, for example), you need only apply a force equal to the weight of the load in order to lift the load. However, moving the fulcrum closer to the load reduces the amount of force you need to lift the load. This makes first-class levers useful for lifting very heavy objects or prying things loose. Figure -. The first-class lever. But there s a catch: Moving the fulcrum closer to the load increases the distance that the effort end must move, while decreasing the distance that the load moves. And therein lies the tradeoff inherent in all simple machines: In order to use less force, that force must be applied over a longer distance (see Figure -). In this activity, students build a first-class lever and use it to lift a load. By moving the position of the fulcrum, they will see for themselves how levers can be used to make their work easier. Distance the load moves Figure -. Trading force for distance. 0 activity Levers for Lifting Distance the effort moves 0
Activity Sheet, Part A Activity Sheet, Part B Levers for Lifting Levers for Lifting. This is a drawing of a first-class lever. Label the arm, fulcrum, effort, and load in the drawing below. 6. How far did the effort and load move each time? Measure with a ruler. Write your answers in the table. load effort Position of Fulcrum Distance Effort Moved (cm) Distance Load Moved Middle Answers will vary. same as effort arm fulcrum Closer to Effort Closer to Load shorter than above longer than above longer shorter. Where is the fulcrum located? in the middle, between the effort and the load. How do the load and effort move? in opposite directions. How much force did you use to lift the load each time? Measure with your push-pull meter. Write your answers in the table. Position of Fulcrum Amount of Force Needed to Lift Load. You know that the closer the fulcrum is to the load, the easier it is to lift the load. But there is a tradeoff. Look at the table above. What is that tradeoff? The closer the fulcrum is to the load, the less force or effort is needed to lift that load. However, that effort moves over a greater distance. Middle Closer to Effort Closer to Load Answers will vary. more force less force. Finish the following sentence. It was easiest to lift the load when the fulcrum was located. closer to the load Guiding the Activity Review with students the definition of a machine: a mechanical device that helps us do work. Ask students to name some of the machines that they use every day. Additional Information Chances are, students will name complex machines machines with more than one moving part, powered by an engine or motor. Write the term simple machine on the board. Tell students that unlike complex machines that have energy sources like electricity or gasoline engines, simple machines have just one (or no) moving part and require only manual force from people or animals to perform work. In fact, simple machines are the basic parts of which complex machines are made. Tell students that there are six types of simple machines. Ask students if they can name any of them. Then tell students that in this activity, they are going to learn about one type of simple machine, called the lever. The six simple machines are lever, wheel and axle, pulley, inclined plane, wedge, and screw. broward county hands-on science Quarter
Guiding the Activity Write the word lever on the board. Ask, What is a lever? Distribute a copy of Activity Sheet, Parts A and B, to each student. Draw Figure - on the board. Explain that a lever is a straight bar that rests on a support and pivots around it. Tell students that there are four parts to every lever, and explain each part as you label the diagram. The arm is the rigid beam or bar. The fulcrum is the support that the arm rests on. The load is the object to be moved, and the effort is the force needed to move the load. Ask, What do you think happens when you push down on the effort end of the arm? Additional Information Students may know a lever as a projecting handle that is moved to adjust something or turn something on or off. Accept all reasonable answers. Students should realize that the arm pivots around the fulcrum, causing the load at the opposite end of the arm to be lifted. If necessary, review the definition of pivot: to swivel or turn around a fixed point. Tell students that this type of lever is called a first-class lever. In a first-class lever, the fulcrum is located between the effort and the load, and the effort and load move in opposite directions. Have students label the diagram of a firstclass lever at the top of their activity sheets and answer questions and. Then tell students that they are going to build a firstclass lever and use it to lift a load. Divide the class into teams of two. Distribute a wooden paint stirrer and a wooden fulcrum to each team. The paint stirrer will serve as the lever arm. Tell them to use their pencils to draw an X in the middle of the lever arm. Then they can position the fulcrum under the X. Tell the partners in each team to place their fingertips on the two ends of the lever and take turns gently pushing down. Ask, How does your lever move? activity Levers for Lifting Students may be interested to know that there are also second- and third-class levers. One lever is not better than another. Each simply has the fulcrum in a different location. (See the Science Extension connection for more information on second- and third-class levers.) Pressing down on one end of the lever causes the lever to pivot around the fulcrum and the other end of the lever to rise.
Guiding the Activity Ask, What does this remind you of? Tell students that a seesaw is a good example of a first-class lever, but that on a seesaw, the children at the ends take turns being the effort and the load. A seesaw works best when the people at each end are the same weight in other words, when the effort is equal to the load. Additional Information Students may suggest a seesaw. If there is a seesaw in the schoolyard, you may want to take the students outdoors for a demonstration (weather permitting). Explain that a lever can also be used to help lift a heavy load using less effort. The following demonstration will show how. Distribute twelve washers and three pieces of tape about cm ( in.) long to each team of two. Tell students to stack the washers and wrap them with two of the pieces of tape to hold them together. Tell them to place the stack of washers at one end of the lever. They can use their third piece of tape to hold it in place. The fulcrum should still be under the X, in the middle of the lever. Have students press down on the free end of the lever and observe what happens. The washers are lifted. Have students press down on the lever again, this time paying attention to the amount of force it takes to lift the washers. Tell students that in order to lift the stack of washers, they had to press down on the lever with a force that was equal to the weight of the washers. Ask, How could you make it easier to lift the stack of washers? Accept all reasonable answers. Have students move the fulcrum closer to the effort (farther away from the load) and press down on the lever again. Ask, Was it easier or harder to lift the washers this time? Ask, What do you think would happen if you moved the fulcrum closer to the load? Students should have discovered that it was harder to lift the washers with the fulcrum moved closer to the effort. Accept all reasonable answers. broward county hands-on science Quarter
6 Guiding the Activity Have students move the fulcrum closer to the load and press down on the lever again. Ask, Was it easier or harder to move the load this time? Tell students that they are going to confirm their observations by measuring the amount of force it takes to lift the load each time. Ask students, How can we measure this? Distribute a push-pull meter to each team. Have students reposition their levers so that the effort end extends several inches over the edge of their desk. Then have students repeat steps,, and 6, this time using their push-pull meters to measure the amount of force it takes to lift the load of washers (see Figure -). Tell students to record their results in the table in question of their activity sheets. When students have finished, ask them to compare the amount of force it took to lift the washers when the fulcrum was in the middle, closer to the effort, and closer to the load. Ask, Which took the least amount of force? Tell students to answer question on the activity sheet. Additional Information Students should have found that it is much easier to lift the load when the fulcrum is closer to the load. Students may suggest using their push-pull meters to measure the amount of force it takes to lift the washers. Students should press down with the pushpull meter very carefully just hard enough to lift the load of washers off the desktop. Pushing down too hard will cause the lever and washers to catapult off the desk. It was easiest (took the least amount of force) to lift the load when the fulcrum was located closer to the load. activity Levers for Lifting 8 8 6 6 O O 6 6 8 8 Figure -. Using the push-pull meter to measure the amount of force applied to a lever.
8 9 Guiding the Activity Finally, have students move their levers back to the middle of their desktops and set the push-pull meters aside. Tell them to repeat the lever experiment, this time observing and measuring the distance that the effort and load each moves (see Figure -). Tell them to record the measurements in the table in question 6. When all teams have finished measuring, ask, What did you notice about the distance that the effort and load moved each time? Tell students to answer question on the activity sheet. Then review their answers by discussing with students the tradeoff inherent in using a lever to do work: In order to reduce the amount of force you need to lift or move a load, you must apply the force over a greater distance. In other words, you trade force for distance. Tell students that this is true not only of levers but of all simple machines, as they will see in later activities. As appropriate, read or review page 6 of the Delta Science Reader Force and Motion. Additional Information To measure the distance that the load and effort each move, have students hold a ruler upright on the desk next to each end of the lever as it performs the work. Measure the effort end first and then the load end. Students should have discovered that when the fulcrum is closer to the load (and the load is easiest to lift), the effort end must travel a greater distance. 0 9 8 6 0 9 8 6 Figure -. Using a ruler to measure the distance that the effort and load each move. broward county hands-on science Quarter
R EINFORCEMENT How can you reduce the amount of force you need to lift the load, without moving the fulcrum? (Answer: Move the load closer to the fulcrum, or apply the force farther away from the fulcrum.) Have students try this themselves. Assessment Opportunity This Reinforcement also may be used as an ongoing assessment of students understanding of science concepts and skills. SCIENCE JOURNALS Have students place their completed activity sheets in their science journals. C LEANUP Collect the push-pull meters, levers (paint stirrers), fulcrums, and stacks of washers, and return them to the kit. Leave the washers taped together. SCIENCE AT HOME Encourage students to conduct their own experiments with levers at home using a ruler as the lever arm, a pencil as the fulcrum, and ten pennies as both the load and the effort. Remind students that they can change the position of the fulcrum, the load, and the effort. How many different ways can they balance ten pennies? 6 activity Levers for Lifting
Connections Science Challenge Introduce and explain the three types or classes of levers: first class, in which the fulcrum is between the load and the effort; second class, in which the load is between the fulcrum and the effort; and third class, in which the effort is between the fulcrum and the load. Use the diagrams shown below and the fulcrum and paint stirrer levers from the activity to illustrate the three types of levers. As you explain each type, identify one or two examples. Then challenge students to offer additional examples. L E F First Class crowbar, shovel, claw hammer used for prying L E F Second Class hinged door, wheelbarrow, bottle opener Science Extension E L F Third Class fishing rod, your lower arm, baseball bat Ask students to look at home and in the tool department of a hardware or gardening store for examples of levers. Ask them to list the examples they find. Point out that some tools such as scissors, pliers, and tweezers incorporate two levers. Ask students to include tools of this type as well. If students have done the Science Challenge connection, challenge them to list the levers by class. (Pliers and scissors are first-class levers, nutcrackers are secondclass levers, and tweezers are third-class levers.) In a follow-up discussion, encourage students to share the examples they have found. Ask volunteers to draw examples on the board and label the positions of the fulcrum, effort, and load. Ask students whether they have ever seen someone use a jack to lift a car in order to change a tire. Which part of the jack acted as the arm? The effort? Was the fulcrum closer to the car or to the person jacking it up? Why? (The handle that was used to pump the jack was the arm, and the pumping motion was the effort. The fulcrum was closer to the car so that less force would be needed to lift it.) Science and the Arts As a continuing project throughout this module, students can create a bulletin board display of various examples of simple machines, beginning with levers in this activity. Encourage students to use creative methods of representing the machines, such as three-dimensional models and actual objects (a pry-type bottle opener, for example) as well as pictures they have cut from magazines or drawn. Science and Health Tell students that the human body contains examples of levers. Encourage students to try to identify some of these. Have them do the following activity to discover one lever in the human body. Stretch out one arm on a desk and hold a ball or other object in your hand. Resting your elbow on the desk, pull your forearm up to your shoulder. Then return your arm to the desk. How does your arm work like a lever? (The forearm is the arm of the lever, the elbow joint is the fulcrum, the object is the load, and the muscles in the forearm and upper arm exert the force to raise the object.) If possible, borrow a model of a human skeleton so that students can observe such levers directly. Science and Social Studies Suggest that students research the use of catapults in ancient times. Some catapults, called ballistas, used huge levers to hurl boulders. The discovery of gunpowder and the invention of the cannon made catapults obsolete. broward county hands-on science Quarter
8 activity Levers for Lifting