PSLE 2012 - Science

[sammifan]

can i ask?

which of da following conclusions r correct?
did u put more stomata found on under or upper side of the leaves?

[Fun fun]

Stomata found underside of leave

[fantasy1]

Hi


If u chked the website for friction, it is stated that friction also acts on objects that are not moving

[verykiasumummy]

sammifan:

can i ask?

which of da following conclusions r correct?
did u put more stomata found on under or upper side of the leaves?

hello sammifan,

whether there are more stomata on the upper or under side of leaves, it depends if they are land plants or aquatic plants..

land plants have upper surface facing the sun, so they have more stomata on the underside so that they would not be losing too much water.

aquatic plants (floating or partially submerged plants) have more stomata on the upper side because their underside of leaves are in contact with water, hence it makes gases exchange more efficient when more stomata are located on the upper side of the leaves..

[verykiasumummy]

btw, u should post ur question in the relevant thread instead of creating a new thread… this saves time on the admin side as they will need to move it over for u…

[sammifan]

fantasy1:

Hi


If u chked the website for friction, it is stated that friction also acts on objects that are not moving

but this time its diff. friction yes correct but not frictional force

[sammifan]

for da stomata ques, is it

-more stomata found on underside or upperside of leaves?

[fantasy1]

I just got this information from yahoo website.

‘A book resting on a flat table, the frictional force is zero.There is no force trying to move the book across the table,so there is no need for a frictional force because there is nothing for the frictional force to oppose.’

[Monsterparent]

My dd's answer was A,B and C for the frictional force question, though I think at their level, stationary object should be taken as no friction because by definition, friction opposes motion.


Few websites mentioned about static and kinetic frictions exist for stationary and moving objects.
http://ffden-2.phys.uaf.edu/211_fall2002.web.dir/ben_townsend/staticandkineticfriction.htm

I wonder if this is a fair and good question to ask a P6 student if it can cause controversy

[creamyhorror]

Monsterparent:

My dd's answer was A,B and C for the frictional force question, though I think at their level, stationary object should be taken as no friction because by definition, friction opposes motion.


Few websites mentioned about static and kinetic frictions exist for stationary and moving objects.
http://ffden-2.phys.uaf.edu/211_fall2002.web.dir/ben_townsend/staticandkineticfriction.htm

I wonder if this is a fair and good question to ask a P6 student if it can cause controversy

The friction acting on the stationary box and surface is 0. This is actually quite clear, since there's no horizontal force acting on the box (meaning that there's no force for friction to oppose). The only controversial part IMO is, should P6 students be aware that a lack of force being applied (e.g. no one pushing the box sideways) means that there's no friction*?


* Which isn't actually true. If you consider a box sitting on a surface which is accelerating, then there is friction acting on the box, even though there's no horizontal force being applied besides friction. That shows that a lack of force applied to the box doesn't mean no friction is acting on the box.