On using Geometer's Sketchpad to teach relative velocity

Transcription

1 Asia-Pacific Forum on Science Learning an Teaching, Volume 4, Issue 2, Article 8, p.1 (Dec., 2003) National Institute of Eucation Nanyang Technological University Singapore Receive 9 Oct., 2003 Revise 8 Dec., 2003 Contents Introuction Computer software an learning of Geometry Example 1: Crossing the river Example 2: To reach the other shore in the quickest possible time Example 3: Concept of the actual system an relative system. Teachers' content knowlege Value ae by using GSP Feeback on using GSP to teach relative velocity Conclusion References Introuction In the current Aitional Mathematics syllabus (Ministry of Eucation, 2000), the topic Relative Velocity has been introuce. This topic involves abstract Mechanics concepts, which are ifficult for both stuents an teachers. Many junior teachers might not have stuie an unergrauate Mechanics course in their unergrauate ays. As Leong & Lim (2003) foun out, effective use of Geometer's Sketchpa * (GSP) was * Geometer's Sketchpa - this is a useful tool in teaching concepts of geometry to Seconary School stuents. It has an official website which is locate at

2 Asia-Pacific Forum on Science Learning an Teaching, Volume 4, Issue 2, Article 8, p.2 (Dec., 2003) able to improve stuents' spatial ability measure by the stuents' performance in geometry achievement test. Since Mechanics, an Relative Velocity in particular, are built up from geometry concept, the use of GSP may be able to offer some hope in assisting stuents to visualize some concepts for this topic. In this note, the uses of GSP to enhance stuents' unerstaning of some ruimentary kinematics concepts will be iscusse. It is hope that teachers will be able to illustrate the concepts without getting stuents into the rigors of teious mathematical computation. All the complicate mathematical computation coul be left to post-seconary level when the stuents take up a course in Applie Mathematics. Computer software an learning of Geometry Some senior teachers groan over the fact that the rigor of geometric proofs, which is very useful to train the stuents in logical thinking, is no longer in the current curriculum. The introuction of computer software into the curriculum always invites fear among the teachers of the loss of stuents' basic mathematical ability. For example, with the introuction of calculators, some teachers complaine that stuents might lose their sense of estimates for basic operations on simple numbers. The same reasoning extens to the use of computer in eucation: with the use of GSP, woul the rigor of training in logical training an the stuents' ability to solve geometry problems be affecte? Hoehn (1997) gave sample activities of exploring worksheets that coul be one with GSP. He suggeste that activities that involve the proof of theorems on geometry coul be one with the software. It is implie that more abstract results on geometry can be taught by focusing on improving stuents' spatial ability. Hoehn further suggeste that stuents coul be aske to attempt to generalize existing theorems an state an verify their conjectures. All this is in line with our new Problem-Solving Approach in the syllabus (Ministry of Eucation, 2000). As Leong & Lim (2003) pointe out, the key features that make the software GSP suitable for teaching transformation geometry are (a) it enables objects to be transforme on the screen; (b) it allows easy measurement of istances, angles an areas; (c) it has the click-an-rag feature that enables users to experiment ifferent cases () it allows animations of motion to be one. Here the above features will be mae use of to enable the teaching of concepts of mechanics more visual than rigorous proofs.

3 Asia-Pacific Forum on Science Learning an Teaching, Volume 4, Issue 2, Article 8, p.3 (Dec., 2003) Example 1: Crossing the river For most stuents learning Relative Velocity, one of the main ifficulties is the resolution of vectors. Thus it is important to ai stuents in visualizing projection of vectors before plunging into the actual concepts of Relative Velocity. Here GSP can be useful to assist stuents in visualizing concept of projection of vectors. One main setting of Relative Velocity is the scenario on "crossing the river". We shall assume that the banks of the river are two parallel lines, as shown in the Figure 1 below. The istance between the two parallel banks, as represente by the two parallel lines, is unit. We shall further assume that the true spee of the boat is kept constant at v at an angle q to the bank θ v True istance Then the time taken by the boat to cross the river Figure 1 true istance true istance = = true spee v...(a) By consiering the projection along the irection marke by the istance in Figure 1 above, another way to compute the time taken to cross the river = v sin θ....(b) Both ways of computation, (A) an (B), give the same time for the boat to cross the river. It may not be easy to convince Seconary school stuents that (A) an (B) give the same time, since the concept of "projection" is not in their Seconary School Science curriculum. For a stuent who is not particularly well verse in trigonometry an geometry, GSP can be use to illustrate this clearly. The worksheet using GSP is introuce in Figure 2 below.

4 Asia-Pacific Forum on Science Learning an Teaching, Volume 4, Issue 2, Article 8, p.4 (Dec., 2003) Figure 2: Worksheet for Example 1 In the above worksheet, the stuents click the button Animate Point on the screen to start the animation of the two points A an B. Initially both points A an B coincie with the point X. Upon clicking the Animate Point button, both points start to move from left to right as shown in the above iagram. The point B represents the actual boat crossing the river while the point A is another particle that is epenent on the movement of B such that (i) AB is always parallel to the bank; an (ii) A an B reach the other shore at the same time. true istance The time taken by the boat B to cross the river can be calculate as, where v the true istance refers to the actual istance travele by the boat B. The time taken by the particle A, through the series of prompting questions in the worksheet (see Figure 2), can be compute as. Since both particles A an B reach the other shore at the v sin θ same time, another way of computing the time taken to reach the other shore can be taken as. In many of the numerical questions in the typical examination questions, the v sin θ use of to compute the time taken to cross the river may be much more v sin θ

5 Asia-Pacific Forum on Science Learning an Teaching, Volume 4, Issue 2, Article 8, p.5 (Dec., 2003) straightforwar. Example 2: To reach the other shore in the quickest possible time Another problem that can be clearly illustrate by using GSP is to fin the shortest time taken to cross the river. Suppose a current flows at a certain velocity w ownstream. A boat is steere at a constant spee v. The irection the course taken is to be etermine by the boat. The question is: what is the irection the boat shoul steer in orer to reach the other sie of the bank in the shortest possible time? θ v True istance Figure 3 We construct the worksheet as in Figure 4 below. In Figures 4 an 5 below, the unit of measurement of time is in secon. The stuents are aske to rag the arrow, the irection of which represents the irection the boat is steere. Once ecie on the irection the boat be steere, the button ANIMATE POINT on the screen can be clicke to emonstrate the path the actual boat travels (see Figure 5). The irection the boat travels represente by GE in Figure 5 will not be the same as the irection of steer of the boat, represente by GD. The point E represents the actual position of the boat while D is the position of the boat if there is no current ownstream. Both points D an E have the same projection along the irection perpenicular to the two parallel river banks. Stuents click an rag the course taken by the boat to allow for ifferent choices of irections steere by the boat. By altering the course to be taken by the boat, the actual path travele by the boat will be altere accoringly. This is immeiately visible from the worksheet itself. The stuents can then be aske to explore on the course taken by the boat in orer to reach the other shore in the quickest possible time by taking ifferent courses in still water.

6 Asia-Pacific Forum on Science Learning an Teaching, Volume 4, Issue 2, Article 8, p.6 (Dec., 2003) Figure 4 Figure 5 The stuents will iscover that the course that the boat shoul take in orer to reach the

7 Asia-Pacific Forum on Science Learning an Teaching, Volume 4, Issue 2, Article 8, p.7 (Dec., 2003) other shore in the quickest possible time is that perpenicular to the two parallel banks. The mathematical rigors of projection will be ispense with while the objective is met. As a bonus to the use of GSP in this case, the stuents will be able to make the following observations with the above file: a. If the boatman steers upstream, the spee of the boat is slowe own compare with the spee he steers, an hence it takes a longer time to reach the other shore; b. If the boatman steers ownstream, the spee of the boat is increase from the spee he steers the boat (the further ownstream, the faster the spee of the boat). However, the istance it has to take to cross the river is much longer, hence the time taken to reach the other shore is also increase. Observations (a) an (b) above are ifficult to emonstrate with the mechanical computation itself; with the use of such animation, the observations are quite visible to the stuents. Example 3: Concept of the actual system an relative system The metho of teaching Relative Velocity is usually the "Reuction to Rest" metho, see National Institute of Eucation 2003, Pp In a system when two particles A an B are moving with constant velocity, it is equivalent to another system where one of the particle (say B) is resting while A is traveling with the relative velocity of A with respect to B. The former system is calle the "Actual System" while the latter system the "Relative System with respect to B". The question which naturally arises is: why are these two systems equivalent? From the geometry point of view, it is just a translation of the origin to the point A, which is suppose to be reuce to rest. However, this is abstract for most stuents as it implicitly involves translation of the system. With the use of animation, the concept of equivalence can be easily brought out. Figure 6 shows the case when both the Actual System an the Relative System (B reuce to rest) are shown in parallel. As the animation button is clicke, both systems will start to move (as in Figure 7). In the Actual system, both particles A an B move whereas in the Relative Velocity, only particle A moves while B is at rest. Stuents will observe that at any point in time, the vector AB, the relative isplacement of A from B, in either the Actual System an the Relative System are equal.

8 Asia-Pacific Forum on Science Learning an Teaching, Volume 4, Issue 2, Article 8, p.8 (Dec., 2003) Figure 6 Figure 7 Stuents can change the initial points of A an B by ragging them to ifferent positions, but the vectors AB in both the Actual System an Relative System will always be equal, regarless of whether A an B are in motion or stationary. The physical meaning of the Relative System is clearly brought out. This is an alternative approach to mechanically "converting" the Actual System into the Relative System by reucing B to rest.

9 Asia-Pacific Forum on Science Learning an Teaching, Volume 4, Issue 2, Article 8, p.9 (Dec., 2003) Teachers' content knowlege In orer to be able to esign worksheets suitable for their stuents, teachers nee to have soun peagogical content knowlege - the amount of knowlege require in the Aitional mathematics syllabus alone is not sufficient. Usiskin (2001) classifies the peagogical content knowlege that a teacher nees to have uner three categories: (1) generalize knowlege from what is require in the syllabus; (2) concept analysis an (3) problem analysis. Possibly one of the reasons why current in-service teachers fin this topic ifficult is that they o not have sufficient peagogical content knowlege for this topic. As such, they fin it ifficult to teach this topic or to esign suitable activities to facilitate their stuents' learning. Value ae by using GSP Consier Example 1: stuents coul acquire a soun unerstaning of the concept of projection of a vector (in this case velocity vector) along a given irection (the irection that is perpenicular to the two parallel river banks) by visual impact, rather than by the true istance traitional rote memory of equating the two expressions = (see true spee v sin θ Example 1). Resolution of vectors forms the founation of Relative Velocity. To be confient in esigning worksheets pertaining to this area, teachers nee to be able to see this from the geometrical concept of similar figures an the relate mechanics concept of resolving vectors. Example 2 is another ifficult concept for stuents to visualize: irregarless of the water spee of the boat, the boat must be steere perpenicular to the two parallel banks in orer to reach the other shore in the shortest possible time. However, with the use of GSP, the following facts can be easily visualize by ragging the ifferent irections of the boat: if the boat is steere upstream, it takes a longer time to reach the other shore since the true spee of the boat is reuce; if the boat is steere ownstream, even though the spee of the boat is increase, it has to travel a much longer istance in orer to reach the other shore. Thus, in orer to reach the other shore in the shortest possible time, he must steer perpenicular to the two parallel banks. Example 3 nees the physical interpretation of the subtraction of two vectors AB as 'treating' A as the origin. So, it is geometrically equivalent to translating the point A back to the same point at all time. The vector AB is the same in both systems. This was the relation of the Relative System an the Actual System. Thus, the concept of "Reuction to Rest" metho of solving problems involving Relative Velocity can be given a more meaningful physical interpretation by using GSP.

10 Asia-Pacific Forum on Science Learning an Teaching, Volume 4, Issue 2, Article 8, p.10 (Dec., 2003) Feeback on using GSP to teach relative velocity The author has conucte a 12-hour workshop on Teaching Relative Velocity for in-service teachers in Singapore. A total of 2-hour was spent on using GSP, with hans-on practice for teachers with the use of appropriate worksheets. At the en of the entire course, participants' feeback was collecte. Two questions pertaining the use of GSP to teach the above concepts relate to Relative Velocity were aske an the feeback were as follows: Questionnaire I think the use of GSP is useful to illustrate the relate Mechanics concepts I woul want to try out using GSP to teach Mechanics Strongly Disagree Agree Strongly Not Disagree Agree Applicable Out of the 35 participants, 18 of them (more than 50%) regare the GSP section of the workshop as being the most useful of the entire course. Currently, the author is working with two schoolteachers who will be teaching Relative Velocity in 2004 in orer to obtain any effect on the stuents' performance after attening lessons on Relative Velocity using GSP. Conclusion Teachers can esign iscovery worksheets to allow stuents to iscover an verify the necessary an sufficient conitions for two particles moving with constant velocities an with ifferent starting points to intercept. All these activities enable stuents to make sense of all the stanar results of Relative Velocity without having to get into the rigors of mathematical computation. The above iscussion gives three examples on how GSP can be use to facilitate stuents to visualize some key concepts in the topic of Relative Velocity. It shoul be note that the above are some recommenations on how the software can be use for teaching; it oes not exhaust all possibilities on how the software can be use in teaching the topic. The rest epens on the teacher's creativity in esigning their files an relate worksheet for their stuents. Eucators shoul not overlook what matters most in ensuring the effective use of technology in classrooms (Bliss T.J., Bliss L.L., 2003). Besies having a soun peagogical content knowlege, teachers must be equippe with reasonable level of

11 Asia-Pacific Forum on Science Learning an Teaching, Volume 4, Issue 2, Article 8, p.11 (Dec., 2003) proficiency of the tool itself. In aition, teachers shoul constantly bear in min that the use of GSP or any other eucational technology is to enhance stuents' learning. References Bliss, T.J. & Bliss, L.L. (2003). Attituinal Response to Teacher Professional Development for the Effective Integration of Eucational Technology. Journal of In-Service Eucation, 29(1), Hoehn, L. (1997). A Concurrency Theorem an Geometer's Sketchpa. The College Mathematics Journal, 28(2), Leong, Y.H. & Lim-Teo, S.K. (2003). Effects of Geometer's Sketchpa on Spatial Ability an Achievement in Transformation Geometry among Seconary Two Stuents in Singapore. The Mathematics Eucator, 7(1), Ministry of Eucation. (2000). General Certificate of Eucation (Orinary Level / Normal Level): Mathematics Subjects Syllabuses, UCLES/MOE, Singapore. National Institute of Eucation. (2003). The Green Book: Resources an Ieas for Teaching Seconary School Mathematics, Singapore. Usiskin, Z. (2001). Teachers' Mathematics: A Collection of Content Deserving to be a Fiel, The Mathematics Eucator, 6(1),