Red River Catastrophe Project

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1 Newton s Third Law INVESTIGATION LESSON Author(s): Date to be taught: Week 1 Technology Lesson: Yes No Course Description: Lesson Source: Name: Physics Grade Level: 12 th Grade Honors or Regular: Regular Stanbrough, J.L. (2009, January 01). Physics 1 newton's third laws. Retrieved from Experiment 7: newton's third law. (n.d.). Retrieved from Accommodations for Learners with Special Needs (ELL, Special Ed, 504, GT, learning styles, etc.): Give clear definitions of vocabulary Check over lab set-up and apparatus when they are working in lab Check over data after the gather before they can do calculations Group students in a cooperative learning environment to help one another Concepts: As a result of the lesson, students will become familiar with Newton s third law. The students will already have covered vectors and equilibrium. Here the students will gain a better understanding of how their bridges will fell the force of the hanging weights. Definitions: Newton s 3 rd Law if two objects interact, the force exerted by object 1 on object 2 is equal in magnitude and opposite in direction to the force exerted by object 2 on object 1. Objectives: SWBAT, explain Newton s Third Law based on the activity that they did SWBAT, relate Newton s Third Law to their bridge project since they will be hanging weights from the bridge to create an equal and opposite force. Texas Essential Knowledge and Skills (TEKS): Physics (c) Knowledge and skills. (1) Scientific processes. The student conducts investigations, for at least 40% of instructional time, using safe, environmentally appropriate, and ethical practices. These investigations must involve actively

2 obtaining and analyzing data with physical equipment, but may also involve experimentation in a simulated environment as well as field observations that extend beyond the classroom. The student is expected to: (A) Demonstrate safe practices during laboratory and field investigations (2) Scientific processes. The student uses a systematic approach to answer scientific laboratory and field investigative questions. The student is expected to: (E) design and implement investigative procedures, including making observations, asking welldefined questions, formulating testable hypotheses, identifying variables, selecting appropriate equipment and technology, and evaluating numerical answers for reasonableness; (F) Demonstrate the use of course apparatus, equipment, techniques, and procedures, including slotted and hooked lab masses meter sticks, scientific calculators, graphing technology, computers (I) identify and quantify causes and effects of uncertainties in measured data; (J) Organize and evaluate data and make inferences from data, including the use of tables, charts, and graphs; (K) communicate valid conclusions supported by the data through various methods such as lab reports, labeled drawings, graphic organizers, journals, summaries, oral reports, and technologybased reports; and (L) Express and manipulate relationships among physical variables quantitatively, including the use of graphs, charts, and equations. (3) Scientific processes. The student uses critical thinking, scientific reasoning, and problem solving to make informed decisions within and outside the classroom. The student is expected to: (A) in all fields of science, analyze, evaluate, and critique scientific explanations by using empirical evidence, logical reasoning, and experimental and observational testing, including examining all sides of scientific evidence of those scientific explanations, so as to encourage critical thinking by the student; (F) Express and interpret relationships symbolically in accordance with accepted theories to make predictions and solve problems mathematically, including problems requiring proportional reasoning and graphical vector addition. (4) Science concepts. The student knows and applies the laws governing motion in a variety of situations. The student is expected to: (D) Calculate the effect of forces on objects, including the law of inertia, the relationship between force and acceleration, and the nature of force pairs between objects; (5) Science concepts. The student knows the nature of forces in the physical world. The student is expected to: (A) Research and describe the historical development of the concepts of gravitational forces; (B) Describe and calculate how the magnitude of the gravitational force between two objects depends on their masses and the distance between their centers; CCRS: I. Nature of Science: Scientific Ways of Learning and Thinking A. Cognitive skills in science 4. Rely on reproducible observations of empirical evidence when constructing, analyzing, and evaluating explanations of natural events and processes B. Scientific inquiry 1. Design and conduct scientific investigations in which hypotheses are formulated and tested. C. Collaborative and safe working practices 1. Collaborate on joint projects 3. Demonstrate skill in the safe use of a wide variety of apparatuses, equipment, techniques, and procedures.

3 E. Effective communication of scientific information 1. Use several modes of expression to describe or characterize natural patterns and phenomena. These modes of expression include narrative, numerical, graphical, pictorial, symbolic, and kinesthetic. 2. Use essential vocabulary of the discipline being studied. III. Foundation Skills: Scientific Applications of Communication A. Scientific writing 1. Use correct application of writing practices in scientific communication VIII. Physics B. Vectors 1. Understand how vectors are used to represent physical quantities 2. Demonstrate knowledge of vector mathematics using a graphical representation 3. Demonstrate knowledge of vector mathematics using a numerical representation. C. Forces and motion 2. Understand forces Materials List: Each group will need the following: Two force probes and a LabPro Logger Pro A skateboard (use the round red skateboard) and string Two Spring Scales Two Pasco Carts with force probe holders attached Masses to place on the carts to increase mass Advanced Preparations: Safety: Get copies of lab. Have students set up apparatus the first day of lab. Closed toed shoes are required in lab.

4 5Es: ENGAGEMENT What the Teacher Will Do Have the students play a game of tug-of-war. Students can go outside and play a quick game of tug-of-war to get their mind thinking about the forces that are being exerted. There are many situations where objects interact with each other. In this investigation we want to compare the forces exerted by the objects on each other. Probing/Eliciting Questions What forces are we experiencing when we play tug-of-war? What factors might determine the forces between the objects? Is there some general law which relates these forces? Is there some general law which relates these forces? Time: Minutes Student Responses and Misconceptions [Force on each other] [Force of the rope] [Mass of the object] [Distance between the objects] [One of Newton s Law] [For every action, there is an equal and opposite reaction] We will begin our study of interaction forces by examining the forces each person exerts on the other in a tug-of-war. Evaluation/Decision Point Assessment Students will be able to state Newton s Third Law. They will realize that the lab will be about equal and opposite forces exerted on each other. Student Outcomes Students will be able to relate Newton s Third Law to the lab and to their bridges.

5 EXPLORATION What the Teacher Will Do Explain to the students the lab. The majority of the work will be left to the students. The students will be finding out Newton s Third Law on their own by the Investigations. Probing/Eliciting Questions Ask the student s questions as you walk around the labdifferent groups of students will have different questions. Some questions are as follow: Why is there an equal and opposite reaction? How does Investigation 1 differ from Investigation 2? Students may also have questions about the LoggerPro software. Time: Minutes Student Responses and Misconceptions Evaluation/Decision Point Assessment Students will complete lab. Student Outcomes Students will have an idea of how their lab defines Newton s Third Law. Also, students will be able to see how this relates to their bridges.

6 EXPLANATION What the Teacher Will Do The fundamental law governing interaction forces between objects is Newton's Third Law, which can be stated: If one object exerts a force on a second object, then the second object exerts a force back on the first object which is equal in magnitude and opposite in direction to that exerted on it by the first object. Go over Investigation 1. Probing/Eliciting Questions How did the two pulls compare to each other? [Equal] Time: Minutes Student Responses and Misconceptions Was one significantly different from the other? [About the same] How did your observations compare to your predictions? [Our predictions are the same] Go over Investigation 2. How did the two pulls compare to each other? [Equal] Was one significantly different from the other? [About the same] How did your observations compare to your predictions? [Our predictions are the same] Evaluation/Decision Point Assessment Students correctly answered the questions. Student Outcomes Students completed lab and correctly answered the questions.

7 ELABORATION What the Teacher Will Do Probing/Eliciting Questions Do your observations in Investigations 1 and 2 support Newton's Third Law of motion? Time: Minutes Student Responses and Misconceptions [Yes, because of an equal and opposite reaction] When you pull on an object with a force probe, does the probe measure the force it exerts on the object or the force exerted on the probe by the object? (Does this distinction have any meaning?) Explain. Lead the class in a discussion about how this will relate to their bridges. IF TIME PERMITS: Talk about collisions. What about unbalanced forces and the result of unbalanced forces? How does this relate to our bridge project? [Unbalanced forces will have different results] [The force on the bridge] [Since we are hanging weights in the center of the bridge, we will experience force in the middle] Newton actually formulated the third law by studying the interaction forces between objects when they collide. It is difficult to fully understand the significance of this law without first studying collisions. Evaluation/Decision Point Assessment Students had thorough discussion on bridges and how Newton s Law relates. EVALUATION Student Outcomes Students will be able to see how the two Investigations and Newton s Third Law relate to their bridge projects. Time: Minutes What the Teacher Will Do & Evaluation/Decision Point Assessment Have students complete Newton s Third Law Quiz. Students will discuss the questions in their groups and then discuss the answers as a class. (

8 Newton's Third Law To every action there is always opposed an equal reaction, or the mutual actions of two bodies upon each other are always equal, and directed to contrary parts. If you press a stone with your finger, the finger is also pressed by the stone. If a horse draws a stone tied to a rope, the horse (if I may say so) will be equally drawn back towards the stone.... Isaac Newton Principia (1686) OVERVIEW We would like to turn our attention to the mutual forces of interaction between two or more objects. This will lead us to a very general law known as Newton's Third Law which relates the forces of interaction exerted by two objects on each other. You will be asked to make some predictions about interaction forces and then be given the opportunity to test these predictions. Investigation 1 Prediction 1 Suppose that you have a tug-of-war with someone who is the same size and weight as you. You both pull as hard as you can, and it is a stand-off. One of you might move a little in one direction or the other, but mostly you are both at rest. Predict the relative magnitudes of the forces between person 1 and person 2. Put an X on your prediction! person 1 exerts a larger force on person 2 the people exert the same force on each other person 2 exerts a larger force on person 1 Activity 1 1. Plug the two force probes into Channel 1 and 2 of the LabPro. Put the eyehooks (top of red box) on the force probes. Make sure both force probes are switched to the same range. 2. Open the Logger Pro. 3. When you are ready to start, Zero both of the force probes. (Click on Zero under the Experiment menu) Then hook a short loop of string between them, hit Start and begin a gentle tug-of-war. Pull back and forth while watching the graphs. Do not pull too hard, since this might damage the force probes. It may be more instructive to make one of the forces negative so you can see them both. If so, under the Experiment menu, go to Setup Sensors, LabPro1, Ch 1, Reverse Direction. 4. Repeat with different people pulling on each side. 5. Sketch one set of graphs on the axes above, or print the graphs and affix them over the axes.

9 Questions (a) How did the two pulls compare to each other? (b) Was one significantly different from the other? (c) How did your observations compare to your predictions? Investigation 2 Prediction 2 Suppose now that you have a tug-of-war with someone who is much smaller and lighter than you. As before, you both pull as hard as you can, and it is a stand-off. One of you might move a little in one direction or the other, but mostly you are both at rest. Predict the relative magnitudes of the forces between person 1 and person 2. Put an X on your prediction! person 1 exerts a larger force on person 2 the people exert the same force on each other person 2 exerts a larger force on person 1 Activity 2 In this activity you will test your prediction about the interaction forces when you are pulling someone on roller skates or a skateboard along the floor. 1. You will use the Spring Scales and the roller cart (or your own skates) for this part. Do not use the Force Probes, you will damage them. Make sure you zero the scales. Hook the two Spring Scales together and pull someone along on the board. Questions (a) How did the two pulls compare to each other? (b) Was one significantly different from the other? (c) How did your observations compare to your predictions?

10 Comment: The fundamental law governing interaction forces between objects is Newton's Third Law. Which can be stated: If one object exerts a force on a second object, then the second object exerts a force back on the first object which is equal in magnitude and opposite in direction to that exerted on it by the first object. Follow Up Questions (a) Do your observations in Investigations 1 and 2 support Newton's Third Law of motion? (b) When you pull on an object with a force probe, does the probe measure the force it exerts on the object or the force exerted on the probe by the object? (Does this distinction have any meaning?) Explain. Comment: Newton actually formulated the third law by studying the interaction forces between objects when they collide. It is difficult to fully understand the significance of this law without first studying collisions.