Nevada Department of Education Standards. Forces and Motion (Physical Science Unifying Concept B)

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1 Simple Machines Through a series of activities and experiments, students will investigate work and its relationship to the six types of simple machines: inclined planes, levers, pulleys, screws, wedges and wheel and axles. Grade Level: 5th-8th Objectives: Students will differentiate the physics definition of work and the common perception of work. Students will formulate the work done on an object given the force and distance. Students will justify how simple machines make work seem easier. Students will categorize examples of simple machines used every day to make work easier Materials: Inclined planes (boards about 1x5x24 in) 1 per group Weights with loop or hook to attach to scale Pictures of each simple machine Examples of simple machines (optional) Spring scales Appendixes: Time Considerations: Activity 1: 10 to 15 minutes Activity 2: 15 to 20 minutes Activity 3: 20 to 25 minutes Related Lesson Plans: Geothermal Energy Nevada Department of Education Standards Forces and Motion (Physical Science Unifying Concept B) P.5.B.1 Students know that, when an unbalanced force is applied to an object, the object either speeds up, slows down, or goes in a different direction P.5.B.2 Students know how the strength of a force and mass of an object influence the amount of change in an object s motion Science Inquiry (Nature of Science Unifying Concept A) N.5.A.3 Students know how to draw conclusions from scientific evidence Background In physics, work is defined as force X distance. In other words, work results from moving an object a given distance by applying a force. Therefore without motion, there is no work being done. Simple machines are used to make work seem easier by providing a trade-off between the force applied and the distance over which the force is applied. For example, if you increase the distance over which you apply a force, you lessen the amount of force you Excellence in Environmental Education Guidelines Strand 1 Questioning, Analysis, and Interpretation Skills (A, B, C, D, F, G) Learners are able to develop question, design investigations, collect information, and draw conclusions in order to learn about the environment. Strand 2.1 The Earth as a Physical System (C, Energy) Students begin to grasp formal concepts related to energy by focusing on energy transfer and transformations. They are able to make connections among phenomena such as light, heat, magnetism, electricity, and the motion of objects. have to apply over that distance in order to do work. It is important to note that simple machines do not lessen the amount of work that is being done, they simply manipulate the variables (force and distance) so that the amount of work being done seems easier. There are six different types of simple machines: the inclined plane, lever, pulley, screw, wedge, and wheel and axle. We use these simple machines alone or in 1

2 combinations everyday to make work easier. An inclined plane is a flat surface set at an angle such as a ramp. It can be used to alter the effort and distance involved in doing work, such as lifting loads. The trade-off is that an object must be moved a longer distance than if it was lifted straight up, but less force is needed so the work seems easier. Everyday examples of inclined planes include: staircases and ramps. Fig. 1 inclined-plane.html A lever is a straight rod or board that pivots on a point known as a fulcrum. The fulcrum can be moved depending on the weight results in the upward motion of the opposite end. The longer the lever arm, the easier work seems. Everyday examples of levers include: a wheelbarrow, a hammer pulling out a nail, crowbars, and bottle openers. A pulley is a wheel that usually has a groove around the outside edge. This groove is for the rope or belt to move around the pulley. Pulling down on the rope can lift an object attached to the opposite end. A single pulley makes work seem easier because it changes the direction in which forces are applied. Block pulleys or pulley systems share the weight of the object being moved and make it seem lighter. Unfortunately, too many pulleys can make work seem harder by adding friction. Everyday examples of pulleys include: flagpoles and cranes. Everyday examples of screws include bolts, light bulbs, and jar lids Fig. 4 westernrifleshooters.blogspot.com/2009_07_01_archive.ht A wedge is two inclined planes joined back to back. Wedges are used to split things and make work seem easier by splitting things a little at a time over the length of the wedge. Everyday examples of wedges are axes, zippers and knives. Fig. 2 Time/Escapements/gearint.html of the object being lifted or the force you wish to exert. Pushing down on one end of a lever Fig. 3 physicsperttu3.blogspot.com/2012/09/ simple-machines-pulley-lab.html A screw is an inclined plane wrapped around a shaft or cylinder. This inclined plane allows the screw to move itself or to move an object or material surrounding it when rotated. Fig. 5 wedge.html 2

3 Lastly, a wheel and axle has a larger wheel (or wheels) connected by a smaller cylinder (axle) that is fastened to the wheel so that they turn together. When a wheel and axle are turned, the wheel will travel a greater distance than the axel but less force is required to turn it. Everyday examples of wheel and axles are doorknobs, screw drivers and steering wheels. Fig. 6 apps/photos/photo?photoid= Simple machines are all around and used everyday to make work seem easier. When more than one simple machine is put together like in a can opener for example, it is known as a complex machine. Preparation Gather all necessary materials. Make simple machine signs with the name and picture of each machine. Cut wood boards (inclined planes) if necessary and create or purchase weights for the experiment. Doing the Activity Activity 1: What is Work? Write work on the board and ask students what they know about work. Explain that in just a few minutes they will be conducting an experiment to determine whether it is more work to push a wall or a chair and justify their answer. Demonstrate how students should push against a wall for a few seconds thinking about how much work is being done and then go back to their seats and push against their chair while thinking about how much work it requires. After students have pushed against both the wall and their chair, they should have a seat and record in their science notebooks which one they think was more work and why. Ask students to share their ideas by a show of hands who thought pushing against the wall was more work and who thought pushing against the chair was more work. Allow at least a couple of students from each side to explain their reasoning. Note- if this is an introduction to work most students will say pushing against the wall was more work because they had to push harder and it didn t go anywhere. The big reveal: Would you believe that you actually did more work when you pushed your chair then when you pushed against the wall? In fact, when you were pushing the wall, no matter how hard you pushed you actually did no work whatsoever. WHY? Students should begin to identify that there was no work done because the wall didn t move. So, what is work? Allow students to think about this and make suggestions. By the end of this brainstorm the definition for work: Work = Force x Distance should be written up on the board Break down the definition and go through each part using the previous examples of pushing against a wall and a chair. Remind students what a force is (a push or pull). Next, connect the previous examples using arbitrary numbers and plugging them into the equation. For example, let s pretend the force applied to both the wall and the chair was 15 and the distance the chair moved was 2 and the distance the wall moved was 0: For the chair this would be: Work = 15 x 2 (30) For the wall it would be: Work = 15 x 0 Have students think about mathematical properties, What s any number times 0? (0) So, if an object doesn t move any distance, no matter how 3

4 much force is applied is there any work being done? (NO) Why? (Because, work is a force acting on an object to move it across a distance or, simply put, making something move. If the object does not move, no matter how much force is applied, there is no work being done) Activity 2: Simple Machines Tell students, today we will be taking a closer look at things we use every day to make work seem easier: simple machines. Write, Simple machines on the board and have students make a simple machines heading in their notebooks. Remind students to keep in mind the definition for work (Work= Force x Distance) throughout their investigations. Ask the students to identify any simple machines they know before explaining the structure of each simple machine and how each of the 6 machines makes work seem easier. Activity 3: Ramp Up the Science Explain to the class that the next experiment will show change when ramps are used to make work seem easier. Demonstrate to the class how to set up their board to create inclined planes of two different lengths. (one steep ramp, one gradual) Emphasize the correct usage of the spring scales and weights: Do not bounce or swing the weight. Pull evenly and with the scale parallel to the board. Start with the weight on the board. Read the correct numbers if your scales have more than one unit of measure. Divide the students into groups of 3-4 and instruct them to measure the force it takes to slowly pull their weight up a steep (short) and a gradual (long) inclined plane. #1- Which requires more force? Why? And #2 Which requires more work? Why? *Write these questions on the board If groups finish early, have the students use the force they measured and the length of the ramp to calculate the work done in each scenario. After all groups are finished and students have had time to record their conclusions, bring the whole class back together and talk about the two questions on the board. Start with force: have students raise their hands showing whether the longer or shorter inclined plane required more force. Next, ask students to raise their hands and show whether they thought the longer or shorter ramp was more work and allow students to defend their answers. EXPLAIN: If some students calculated the actual work done, use their answers to note that according to physics, using the longer ramp is more work. Remind the students that what many people think of as work is actually the amount of force applied, or how hard they have to push or pull just like the very first activity. Note that all the students discovered that less force was necessary to pull their weights up the longer ramp so the work SEEMS easier even though more work is really being done. (increased work may be due to frictional forces and other mitigating factors) Return to the work equation and demonstrate with easy numbers how changing the distance changes the force necessary. Activity 3: Machine Roundup Ask the students to identify either where the extra length is in each simple machine or tell how each machine makes work seem easier. Tell the students you are going to give examples of everyday simple machines and it is their job to determine which machine is part of that object. Give examples not previously discussed and have the 4

5 students move to the sign that gives the correct simple machine for that object. Conclusion Review the difference between what most people consider work and how work is defined in physics. Assessment Have students go for a simple machine hunt around the school or around their house. Extensions Have students go for a simple machine hunt around the school or around their house. Have students build simple machines and use them to accomplish work. Introduce students to the concept of complex machines (two or more simple machines combined together). Have students dissect complex machines and identify the simple machines that make Sources them up. Vocabulary Work: A force acting on an object to move it across a distance. (Force x Distance) Simple Machines: Inclined planes, levers, wedges, screws and wheel and axles which make work easier. Inclined Plane: A sloping surface, such as a ramp. It can be used to alter the effort and distance involved in doing work, such as lifting loads. Lever: A straight rod or board that pivots on a point known as a fulcrum. Pulley: A wheel that usually has a groove around the outside edge. This groove is for the rope or belt to move around the pulley. Work is made easier because pulling down on the rope is made easier due to gravity. Wedge: Two inclined planes joined back to back. Wedges are used to split things. Screw: An inclined plane wrapped around a shaft or cylinder. This inclined plane allows the screw to move itself or to move an object or material surrounding it when rotated. Wheel and Axle: A larger wheel (or wheels) connected by a smaller cylinder (axle) and is fastened to the wheel so that they turn together Images: Fig. 1 Fig. 2 Fig. 3 Fig. 4 Fig. 5 Fig

6 What is this Simple Machine? How is this simple machine used? (What is it used for?) How does this simple machine make work seem easier? (HINT: think about the equation for work: *Force x Distance*) What are some everyday examples of this simple machine? What is this Simple Machine? How is this simple machine used? (What is it used for?) How does this simple machine make work seem easier? (HINT: think about the equation for work: *Force x Distance*) What are some everyday examples of this simple machine? 6

7 SIMPLE MACHINE HUNT WRITE-UP Object: What simple machine is this object? SIMPLE MACHINES AROUND THE ROOM: (List as many simple machines you can find in the room) How is this object used? How does this object make work seem easier? SIMPLE MACHINE HUNT WRITE-UP Object: What simple machine is this object? SIMPLE MACHINES AROUND THE ROOM: (List as many simple machines you can find in the room) How is this object used? How does this object make work seem easier? 7