PSLE 2012 - Science
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rains:
I think it is a typing error. It should be the science teacher saw the question and not the answer.Yapyap:
My bother, whose sc teacher saw the answers, says that she said the the answer to the frog/tadpole question is that the tadpoles don't compete with the frogs for food, and if predators eat the frog, they cannot eat the tadpoles.
Eh, you want to bluff also cannot bluff until like that lah. Psle marking hasn't started and the teacher got to see the answers ah? I think even principals also cannot see yet leh.
And tadpoles and frogs eat different types of food. How can competition for food be possible?
Tadpoles eat insects and frogs eat algae or plants ah? -
I have just gone through the previous postings on the friction question again. I saw a brilliant answer using static coefficient of friction to justify the existence of ‘potential friction’. This can only be from a student who read beyond the syllabus.
Can we justify penalising the exceptional students who have chosen the answers according to this concept?
I saw also arguments using "potential movement" to justify another answer. I have raised a counter example of a balancing force vector such that there will be no net force and therefore no friction but yet there is potential movement. If the concept is used to answer this question in physics, it would be marked clearly wrong. There is no such thing as potential movement.
Who do we penalise and who to reward?
I will also argue for those who are so affected that they cannot choose any answer and leave it blank. If you have been taught that friction exists during motion only, what would you have chosen? Would they be faulted or is it the P6’s teachers fault for not be able to bring across concepts of forces, equilibrium to a simple level so that the question can be tackled. And then again, doing so would require some degree of spotting the question? -
Also, I have mentioned that there is a possibility of a ‘frictionless surface’, ie,
object is free to slide down without any frictional force.
I feel they should omit the question. -
Friction is such a difficult topic. Perhaps it is good to remove it from the syllabus. If it is to remain, then it may be necessary to highlight all the more common \"exceptions\".
Just 2 examples of common misunderstanding regarding friction from past primary questions :
Question : Does a bald tyre has more or less friction than a normal tyre with threads? Why?
Standard answer : A bald tyre has less friction because it has no thread. The thread helps to increase the friction.
The truth : A bald tyre has the about same friction as a normal tyre if the road is dry. However, on a wet road, the friction of a bald tyre will be greatly reduced because there is a film of water acting as lubricant between the tyre and road surface. For a normal tyre, the threads provide gaps for the water to escape thus reducing this film of lubricant and increases the friction.
Standard Question : Does objects with smooth surfaces have more friction when they come into contact with each other than objects with rough surface?
Standard answer : Objects with smooth surfaces will have less friction when they come into contact with each other than objects with rough surface.
The truth : It depends. If the surfaces are highly polished and they are of the same material, the objects with smooth surfaces will have much higher friction if there is no dirt or oil on the surfaces. This is because the atom/molecules will develop bonds across the surface, causing the 2 surfaces to stick to each other.
Therefore, it is not very good to teach such topic to Pr kids without proper understanding. These wrong concepts will be carried to their adult life. -
AWSP:
It reminds me that there was a year where the MOE gave marks to all the students regardless of their answers. It was due to a flawed Math question. Maybe the kids can check the answer with their own school science teachers. The schools could clarify with MOE.I have just gone through the previous postings on the friction question again. I saw a brilliant answer using static coefficient of friction to justify the existence of 'potential friction'. This can only be from a student who read beyond the syllabus.
Can we justify penalising the exceptional students who have chosen the answers according to this concept?
I saw also arguments using \"potential movement\" to justify another answer. I have raised a counter example of a balancing force vector such that there will be no net force and therefore no friction but yet there is potential movement. If the concept is used to answer this question in physics, it would be marked clearly wrong. There is no such thing as potential movement.
Who do we penalise and who to reward?
I will also argue for those who are so affected that they cannot choose any answer and leave it blank. If you have been taught that friction exists during motion only, what would you have chosen? Would they be faulted or is it the P6's teachers fault for not be able to bring across concepts of forces, equilibrium to a simple level so that the question can be tackled. And then again, doing so would require some degree of spotting the question? -
mummy so kiasu:
Agreed. That is the right way to go about it, apart from having concerned forumers going to the proper authority which is the MOE to seek clarifications etc. I am sure any feedback obtained and posted to this forum will definitely benefit all.
Maybe the kids can check the answer with their own school science teachers. The school could clarify with MOE.AWSP:
I have just gone through the previous postings on the friction question again. I saw a brilliant answer using static coefficient of friction to justify the existence of 'potential friction'. This can only be from a student who read beyond the syllabus.
Can we justify penalising the exceptional students who have chosen the answers according to this concept?
I saw also arguments using \"potential movement\" to justify another answer. I have raised a counter example of a balancing force vector such that there will be no net force and therefore no friction but yet there is potential movement. If the concept is used to answer this question in physics, it would be marked clearly wrong. There is no such thing as potential movement.
Who do we penalise and who to reward?
I will also argue for those who are so affected that they cannot choose any answer and leave it blank. If you have been taught that friction exists during motion only, what would you have chosen? Would they be faulted or is it the P6's teachers fault for not be able to bring across concepts of forces, equilibrium to a simple level so that the question can be tackled. And then again, doing so would require some degree of spotting the question?
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however the problem is, which parent / p6 student will go clarify with their teacher now?? they are all enjoying and relieving themselves…
and again, even when a parent or student volunteers to ask their teacher, will the sci teacher give us a wrong answer since it seems to have so many different perceptions?
come to think of it, after reading the views of the friction question from so many "experts" here. will u agree to any of the answers that the teacher gives? that is, if the teacher says, "yes, friction exists in all surfaces of contact so all of the set ups have friction" — will all here agree??
and if the teacher says, "no, friction only occurs when there is motion force, since all objects are stationary, there is no motion force to oppose in the stationary set ups A and B so there is no friction between them and only in C." ---- will all agree this instead?
i have guts feel that the question posted should be whether gravitational potential energy exists in all 3 set ups, not frictional force.
re-quote the question posted by mum of 3 :
I believe the MCQ question that has been hotly debated is whether frictional force acts on the object shown in 3 pictures which are : A) stationary object on level ground B) stationary object on a ramp or slope C) object moving down a ramp or slope. The choice of answers includes (i) A, B & C (ii) B & C (iii) C only - not in order. -
verykiasumummy:
Yes, I have no doubt there will still be tons of views even after students verified their teachers. We just have to hope for the HOD for Science of schools pursuing this question on behalf of students will be proactive to seek clarification from MOE for the official version.however the problem is, which parent / p6 student will go clarify with their teacher now?? they are all enjoying and relieving themselves...
and again, even when a parent or student volunteers to ask their teacher, will the sci teacher give us a wrong answer since it seems to have so many different perceptions?
come to think of it, after reading the views of the friction question from so many \"experts\" here. will u agree to any of the answers that the teacher gives? that is, if the teacher says, \"yes, friction exists in all surfaces of contact so all of the set ups have friction\" --- will all here agree??
and if the teacher says, \"no, friction only occurs when there is motion force, since all objects are stationary, there is no motion force to oppose in the stationary set ups A and B so there is no friction between them and only in C.\" ---- will all agree this instead?
i have guts feel that the question posted should be whether gravitational potential energy exists in all 3 set ups, not frictional force.
re-quote the question posted by mum of 3 :
I believe the MCQ question that has been hotly debated is whether frictional force acts on the object shown in 3 pictures which are : A) stationary object on level ground B) stationary object on a ramp or slope C) object moving down a ramp or slope. The choice of answers includes (i) A, B & C (ii) B & C (iii) C only - not in order.
IMHO, a student could be expected to tackle this MCQ question in this manner:
Picture (c) - object moving down a ramp or slope
As stated, the object is in motion. This means that kinetic friction is at play because the frictional force is acting against the object zooming down the ramp/slope. Both the weight of the object and gravity contributed to the normal force. Therefore, there is force opposing force.
Picture (b) - stationary object on a ramp or slope
As stated, the object is stationary on a ramp or slope. So why did it not slide down like the one shown in picture(c) where the weight of object and gravity combined will generate the normal force? Here static friction is at play because the normal force is not able to overcome the frictional force. Thus the object stays where it is on the ramp/slope. Therefore, there is force opposing force.
Picture (a) - stationary object on level ground
Unless the object is a ball or an object without complementary flat surface to the ground it is resting on (i.e. can be affected by factors such as wind, etc), it is viewed as an object resting motionless on the level ground. The keyword here is 'level'. The full weight of the object is being pulled down by gravity alone. There is contact sure, but no force opposing force.
Therefore, (b) and (c) is the answer.
Unfortunately, students and parents of their DCs whose answer is other than the above will likely to disagree. Conversely, those whose answer is similar to the above will agree. I suppose this will always be the case even when we obtained the official answer. This is life, and perhaps life of a kiasu parent.
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MeKiasuLeh:
I am sorry to see the answer as such. What is normal force? (does the full force acts on it?) what is force opposing force? A garbled reasoning is as good as a wrong answer. The danger is as what atutor2001 posted about \"bringing forward a wrong concept into later stages of learning\".
IMHO, a student could be expected to tackle this MCQ question in this manner:
Picture (c) - object moving down a ramp or slope
As stated, the object is in motion. This means that kinetic friction is at play because the frictional force is acting against the object zooming down the ramp/slope. Both the weight of the object and gravity contributed to the normal force. Therefore, there is force opposing force.
Picture (b) - stationary object on a ramp or slope
As stated, the object is stationary on a ramp or slope. So why did it not slide down like the one shown in picture(c) where the weight of object and gravity combined will generate the normal force? Here static friction is at play because the normal force is not able to overcome the frictional force. Thus the object stays where it is on the ramp/slope. Therefore, there is force opposing force.
Picture (a) - stationary object on level ground
Unless the object is a ball or an object without complementary flat surface to the ground it is resting on (i.e. can be affected by factors such as wind, etc), it is viewed as an object resting motionless on the level ground. The keyword here is 'level'. The full weight of the object is being pulled down by gravity alone. There is contact sure, but no force opposing force.
Therefore, (b) and (c) is the answer.
:
The issue which I am pushing for is not about marks. The ambiguity of the question is not removed in this question. That is the fault of the setter. And further to that the fully correct answer can only be derived by drawing on knowledge of vectors and static equilibrium. Not by the few rules given to the students in P6. Are the teachers able to articulate the concept to students when they teach without drawing upon higher concepts like force vectorisation? Is the setter taking this into consideration when he set the question?MeKiasuLeh:
The big question goes beyond this exams. Questions like the frog and tadpole are another cause for concern. What is the expectation in the marking scheme? Is the examiner going to mark all else wrong unless it fits into a certain concept that is deemed as the only correct concept to apply? Where a long list of answer abounds?Unfortunately, students and parents of their DCs whose answer is other than the above will likely to disagree. Conversely, those whose answer is similar to the above will agree. I suppose this will always be the case even when we obtained the official answer. This is life, and perhaps life of a kiasu parent.
Could we allow this trend to continue for next year and so on? I heard from my child that some of his classmates cried. So what if everyone gets the same marks for the flawed questions, can we compensate for those who are so affected by these question that they did not perform to their standard? -
In certain societies around the world, the only acceptable answer to the question of why a tadpole lives in water and a frog on land would be : Because GOD made it so.
But this is a forum about PSLE Science, not religion. And one of the most wonderful things about scientist is that they never relied on assumptions. Why did no one wonder about why apples fall to the earth before Newton came to ponder the question? Isn’t it common sense that apples fall to the earth?
To me the bottom line is what are we training our kids? Do we train them to accept common sense assumptions and reason from there? Or do we train them to question all assumptions, to come up to test accepted boundaries? Push the limits.
This is just PSLE, the first of many major exams to come. Some students who do well in PSLE go on to barely making it through A Levels, while some whose grades are average or just above average at PSLE may do brilliantly in Uni.
As a society, its good to have a variety. Too many people pushing the limits may produce too many opposition politicians.
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