Balanced and Unbalanced Forces

Transcription

1 1 Balanced and Unbalanced Forces Lesson Created by Carlos Irizarry, George B. Swift Specialty School, Chicago, Illinois Purpose To fully appreciate and make a connection to Newton s Laws, students must explore how unbalanced forces cause an object to move. Students must also be able to quantify force to better understand the nature of balanced and unbalanced forces. Overview Students will use the Fourier force meters to investigate the net force of a sliding block and observe how greater unbalanced force results in greater motion. Students will also observe how balanced opposing forces create net zero force which results with zero motion. Students may also explore how greater or lesser weight of an object requires greater or lesser force to move that object. Using the HP force meter and tablets, students are able to record their observations quantitatively. Students also develop force diagrams to publish their findings. Student Outcomes Illinois State Standards: 11.A.3c: Collect and record data accurately using consistent measuring and recording techniques and media. 11.A.3f: Interpret and represent results of analysis to produce findings. 12.D.3a: Explain and demonstrate how forces affect motion. National Science Education Standards: 8ASI1.3: Use appropriate tools and techniques to gather, analyze, and interpret data. The use of tools and techniques, including mathematics, will be guided by the question asked and the investigations students design. The use of computers for the collection, summary, and display of evidence is part of this standard. Students should be able to access, gather, store, retrieve, and organize data, using hardware and software designed for these purposes. 8ASI2.4: Technology used to gather data enhances accuracy and allows scientists to analyze and quantify results of investigations. 8BPS2.1: The motion of an object can be described by its position, direction of motion, and speed. That motion can be measured and represented on a graph. Balanced & Unbalanced Forces Teacher Overview 3 pages

2 2 Time One 45- minute class period Level 8 th Grade Physical Science Materials and Tools HP tablet computer HP 39gs graphing calculator emulator software HP force meter (DT272) HP StreamSmart 400 Multiple weighted blocks Rubber bands String, yarn, etc. Preparation Test all force meters and HP tablets and make certain they are operational. Ensure that there are enough materials available to students to support student autonomy. Students will need a large, flat working surface. Prerequisites Students should have a working understanding of forces, friction, weight, gravity, and resistance. Force diagrams should have been modeled and practiced prior to this activity. Background Students should also be well trained in using the HP force meter and gathering data on the HP tablets. Balanced & Unbalanced Forces Teacher Overview 3 pages

3 3 Teaching Notes A class tug- o- war activity can be a very fun and powerful activity to help solidify their budding understanding of these concepts. Weighted blocks can be substituted for any other materials that have some weight and small resistance to moving. This work is supported by a grant from Hewlett- Packard under the HP Catalyst Initiative. However, any opinions, findings, conclusions and/or recommendations are those of the investigators and do not necessarily reflect the views of the funders. Balanced & Unbalanced Forces Teacher Overview 3 pages

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5 1 Review: Balanced and Unbalanced Forces It is important to remember that force can be described as a push or a pull. When one object pushes or pulls a second object, one can say that the first object is exerting a force upon the second object. Much like when a soccer player kicks a soccer ball, the soccer player (the first object) kicks the ball (the second object) thereby exerting a force onto it. You exert a force whenever you lift, turn, carry, or throw something. You exert a force even when standing still! Remember: what s the force that is always exerted upon us while we are on Earth? We try to resist this force every time we stand, walk, run, climb, etc. Remember also our discussion on balanced and unbalanced forces. When the forces put upon an object are balanced, the forces will not change the object s motion. However, when the forces are unbalanced the object s motion will change. Remember net zero force means zero change in motion. How is standing still an example of forces in balance? How is falling downstairs an example of forces that are unbalanced? Do NOT demonstrate! Challenge: Today we will explore how an object s mass, the force(s) exerted upon it, and the changes in its motion are all interrelated. Think aloud with your group Does the amount of force exerted upon an object affect its motion? How does changing the mass/weight of the object affect the amount of force needed to set the object in motion? Balanced & Unbalanced Forces Student Guide 3 pages

6 2 Procedure 1: 1. Place one block upon the table, and hook two force meters to it (one to each side as previously demonstrated). 2. Two group members should each take a force meter and pull the block so that it reads 1 N on each meter. 3. Observe the block. In your science notebook, draw a force diagram similar to the example below. On your force diagram record the forces on the block from Step 2. Discuss with your team and explain in your notes why the block is not in motion. 4. Have one group member gently pull the block with the force meter at 1.5 N, while the other group member pulls steady with the force meter staying at 1 N. 5. Observe the block. In your science notebook, draw another force diagram. On your force diagram record the forces on the block from Step 4. Discuss with your team and explain in your notes why the block IS in motion. 6. Give other members of your team the opportunity to carry out Step 4 and observe changes in motion with changes of force. 7. Discuss with your group: Does the amount of force applied to the block change its motion (direction and speed)? Draw conclusions and record your group s thoughts in your notes. 8. Discuss with your group: Which force diagram should be labeled Zero Net Force? Which force diagram should be labeled Non- zero Net Force? Which diagram shows balanced forces? Which diagram shows unbalanced forces? 9. Label each diagram accordingly. Force Diagram Template N Block N Balanced & Unbalanced Forces Student Guide 3 pages

7 3 Procedure 2: 1. Have one group member attach one force meter to the ½ kilogram block and gently increase the amount of force used to pull the block until it begins to move. In your science notebook, record the minimum amount of force required to set the ½ kilogram block into motion. 2. Repeat Step 1 using the 1 kilogram block. 3. Repeat Step 2 using the 3 kilogram block. 4. Organize your information into a clear and comprehensible data table of your own design. 5. Allow all members of your group the opportunity to manipulate the blocks with the force meters. Discuss your observations. 6. Think and discuss with group: What seems to be the relationship between the mass/weight of an object and the amount of force required to set it in motion? 7. Organize your thoughts with your group and be prepared to share out your group s theories. Use your data table to support your thinking. Balanced & Unbalanced Forces Student Guide 3 pages