AWSP:

I have a little parody on the question on friction.

A teacher is teaching students John and Mary how to answer a question on friction. (Reference a,b,c).
Teacher: In c, the object is moving down the slope because the gravitational force is greater than friction. Whereas, in b, the gravitional force is less than friction so it is not moving.
John: But teacher, I thought gravitational force is the same no matter how steep is the slope. Does it mean that there is greater gravitational force when we stand on the top of the stairs?
But the teacher cannot teach vectorisation of forces.
Teacher: No, gravitational force is the same on top of the stairs as below. But on the slope, it is greater. TRUST ME. This is PSLE science WANTS you to know. Remember you slide down easier when the slope is steeper.
Teacher: Now in a, there is no movement so there is no friction.
John: But in b, there is also no movement so there is no friction.
Teacher: In b, the gravitational force is greater than on b. TRUST ME. This is PSLE.
During PSLE, the same question came out. (Note this is only a hypothetical play).
John asks Mary: Did you get the question on friction correct? I got confused because I start asking the same questions again.
Mary: Yes, I got it right with a lot TRUST.

MeKiasuLeh:

IMHO, @verykiasumummy and @atutor2001 answers to the frog/tadpole question would readily be acceptable. I did not read all threads so there might be more worthy ones.


This is a booklet B question, and I believe most questions in booklet B require students to demonstrate their knowledge of Science, it's application, as well as reasoning skill. And for this reason, PLSE markers will be asked to mark \"holistically\", a terminology used widely in the answer key found in RGPS exams marking scheme. Probably RGPS uses the same format (answer key) as MOE or vice versa. I also believe, like in most schools, each paper is marked then verified by another before the final score is set in stone.

How do one tackle such a question? First, we know its biology we are dealing with and one of the first things that should come to mind is that a tadpole is the young of a frog and a frog is an amphibian, both of which are living things that need a conducive habitat to survive in. Next, we ask ourselves a series of questions e.g. Do they live on their own? Does one need to know about life cycle of a frog? Where is the food source of a frog and tadpole? Also, do we need to consider the stages that a tadpole has to go through before being an adult? Articulating the answer would be the challenge but I believe keeping within these premise should be safe and it is best to keep the answer within a natural setting (i.e. avoid throwing disasters, like fire, drought, etc into the mix).

I am inclined to answer this way .....

A frog is an amphibian which lay eggs on water, leaving their young, the tadpole, to survive on their own in its life cycle. Frogs feed mainly on insects and other small creatures that can be found mostly on land whereas tadpoles feed primarily on plants, mainly aquatic plants which can be found mostly in water. Frogs are more agile on land than on water, and this helps them avoid predators and find food better, thus ensuring their survival. On the other hand, tadpoles, which do not resemble their adults particularly in their initial stage of development, has no or ineffective limbs. Therefore, tadpoles are inherently adaptable to water than on land, allowing them to move better to find food and avoid predators. These are the advantages for frog to live on land and for tadpoles to develop into adulthood in water.

How much to write? I will use the space provided in the booklet as a guide. Now, I truly do not know what the right answer is, or will my proposed answer be acceptable. It might just managed to elicit a sly smile from the marker but no marks! But so long as a student keep it within a logical framework and mentioned key things like \"survival\" and \"Food source\" and relate these to land and water and demonstrate what habitat means, I believe he/she should be safe.

For those die die must know 'the right answer' then I suggest he/she tap on VitaMindZ. I heard the folks there used to set PSLE Science questions and the top PSLE girl last year had her tuition in that centre. But for me, I believe a student should practice using his/her own intuition, learn to perform own research, interact with fellow students and consult teachers/parents as much as they can for the real challenge is after P6.

creamyhorror:

atutor2001:

...


A force on objects or substances in contact with each other that resists motion of the objects or substances relative to each other. Static friction arises between two objects that are not in motion with respect to each other.

Friction is the force between surfaces in contact that resists their relative tangential motion. Static friction occurs when the two surfaces in contact are not in relative motion; that is, when one surface is stationary relative to the other surface.

....

\"Static friction occurs when the two surfaces in contact are not in relative motion\"
[*] Similarly, this definition doesn't use \"occurs whenever\" or \"occurs every time when\", and so does not cover all cases where surfaces are in contact without relative motion. What it's actually doing is defining a negative condition (\"not in relative motion\") in order to distinguish static friction from kinetic friction.

creamyhorror:

Really, there's no point in debating what the proper answer is, because it's a matter of definition. What most of us can agree is on is that a P6 student can't be fairly expected to answer the question, if (1) the knowledge to answer it is beyond the syllabus, and (2) there are grounds for alternative answers given the definition of friction that is taught.

This is the sort of question that should be considered for nullification/striking off. I appreciate AWSP's arguments against questions that may accept too narrow a range of acceptable answers: if you ask an application question that isn't clear-cut, you should be willing to accept a broader scope of reasonable answers. This is the same thing we saw in the PSLE Chinese exam: multiple MCQ options that are acceptable (e.g. 偏僻，寂寞，孤单), but probably only one correct answer based on a narrow view of what counts as \"proper style\".

A stiff-minded approach to setting acceptable answers - or setting overly ambiguous questions - is simply a bad way to set exams.

Nebbermind:

Adding on to MeKiasuLeh's reply,

MeKiasuLeh:

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.

This setup is not in equilibirum. Therefore, if you draw a http://en.wikipedia.org/wiki/Free_body_diagram, u will have one force acting normally on the object by the slope, another (gravitational) force pointing vertically down from centre of the object, and another one parallel to the slope, pointing from the object to the end of the slope. As there is no info on whether the slope is frictionless or not, we may or may not have a (frictional) force component acting upwards along the slope due to the object accelerating down the slope.

So no way to tell if there is frictional force or not, unless we assume that any surfaces in contact should have some and frictionless contact does not exist.

MeKiasuLeh:

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.

MeKiasuLeh:

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.

MeKiasuLeh:

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.

MeKiasuLeh:

verykiasumummy:

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.

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.

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.

atutor2001:

From the above 2 sites, the definition of friction are :


A force on objects or substances in contact with each other that resists motion of the objects or substances relative to each other. Static friction arises between two objects that are not in motion with respect to each other.

Friction is the force between surfaces in contact that resists their relative tangential motion. Static friction occurs when the two surfaces in contact are not in relative motion; that is, when one surface is stationary relative to the other surface.


Unfortunately, in primary school, they only emphasizes that \"friction opposes motion\". I believe the definition of friction was not taught. Neither is the existence of static friction (as given by physics definition) being explained. This gives rise to questions as to whether there is friction when the object is stationary with no lateral force being applied. However, if the definition of friction is accepted and known to every student, then there will be no ambiguity. Everyone will accept that a stationary object has static friction, as defined by the definitions on friction.

AWSP:

MeKiasuLeh:

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.
:

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\".

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:

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.

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?

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?

MeKiasuLeh:

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.
:

MeKiasuLeh:

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.

verykiasumummy:

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.

mummy so kiasu:

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?

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?

rains:

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?

Nebbermind:

rains:

Aiya, so incidental that I happen to be the marker lor - that's how I know he's bluffing! Ya lor. Psle over one week already. What's there to discuss? Then you still come and discuss for what?

:rotflmao:
Good one there!

atutor2001:

AWSP:

....
But, what are we testing? ....Why does the turtle lay eggs on the beach? Why is it that caterpillar and butterfly are both on land?
Is it just randomness of nature in the frog's evolution?
What if we put randonmness of nature in the frog's evolution - will that be right or wrong? Why should we mark it wrong?

You have brought up a very valid point i.e. what is the purpose of this question. Hope the authority does follow this forum and take note of your point.