Q&A - PSLE Science

[kelly1]

atutor2001:

kelly1:

This is referring to the question about how the stem of a flower is slit in half, then dipped in coloured water on each side. The correct solution says that the xylem tubes in each half will take on the respective colour of the water where that half is dipped. My question is, can the stem also absorb water? The roots have been cut off in this diagram.

Yes, there is a special mechanism in the xylem that enables the water to flow upwards. Sugar cane (a stem) left standing with its cut end resting on dirty wet floor in hawker centre will absorb the dirty water and caused food poisoning. It happened locally before.

Thanks! Now the question makes sense...

[James Ang]

The whole of science is nothing more than a refinement of everyday thinking.

Albert Einstein

[tianzhu]

Thank you for your help.


1) SwimTeam Company wants to make swimming boards and chose styrofoam as a material. Which of the following properties make styrofoam a suitable material for making swimming boards? (a) Styrofoam can float on water (b) Styrofoam does not break or tear easily Styrofoam is light so it can be carried easily (d) Styrofoam is soft so it would not injure anyone. Answer options -> (1) a, b and c only (2) a, c and d only (3) b, c and d only (4) all of the above.


2) What must happen for an egg to hatch? (a) The egg must be fertilized. (b) The egg must be given food and water. The egg must be kept warm by the hen for 21 days. Answer options - > (1) a and b only (2) a and c only (3) b and c only (4) All of the above.

[Tang]

tianzhu:

Thank you for your help.


1) SwimTeam Company wants to make swimming boards and chose styrofoam as a material. Which of the following properties make styrofoam a suitable material for making swimming boards? (a) Styrofoam can float on water (b) Styrofoam does not break or tear easily (c) Styrofoam is light so it can be carried easily (d) Styrofoam is soft so it would not injure anyone. Answer options -> (1) a, b and c only (2) a, c and d only (3) b, c and d only (4) all of the above.

Answer given in the worksheet is not correct. It should be (4). The styroform must not break or tear easily, otherwise the person using it may drown. Styroform used for making swimming boards and boxes can be very robust and will not tear or break easily.


2) What must happen for an egg to hatch? (a) The egg must be fertilized. (b) The egg must be given food and water. (c) The egg must be kept warm by the hen for 21 days. Answer options - > (1) a and b only (2) a and c only (3) b and c only (4) All of the above.

Answer is (2).

[Cando]

[Moderator's note: Topics merged.]


I was asked this question : why do we need to sprinkle water on clothes while ironing? Does it help to straighten the wrinkle? How?

Can anyone help?

Thank you in advance.

[Cando]

I was asked this question : why do we need to sprinkle water to clothes while ironing? Does it help to straighten the wrinkle? How?


Can anyone help?

Thank you in advance.

[TTLauPeh]

Synthetics don’t wrinkle so I assume the question refers to cotton garments. What you spray water on cotton material and then iron it, what happens is:

1) The fibres in the cotton material absorbs the water.
2) The water molecules in the fibres are attracted to one another and the air between the fibres is forced out, flattening out the wrinkle and making the fabric tighter. [Similarly, cotton balls shrink when you wet them and wrinkling in curtains can be reduced by just vacuuming them].
3) Heat from the iron evaporates the water, leaving a wrinkle-free patch of cotton fabric.

[Cando]

tianzhu:

Rate of evaporation


One of the factors affecting the rate of evaporation is temperature.

When we are talking about temperature, does it refer to temperature of the source or temperature of the surroundings? For example a cup of hot water as compared to a cup of warm water in airconditioned/non airconditioned room, clothes left to dry under shade or out in the sun.
Please share your view.

Thank you for your reply

[kelly1]

Question about Gravitational Potential Energy:

1) Object on ground, near a well
2) Object in the well.
Do they both have no GPE, or does the object on the ground still have some GPE (just because the object shown relative to it is actually below ground level, in the well)?

What about objects lying on the floor, but say in a high-rise apartment?
TIA

[atutor2001]

kelly1:

Question about Gravitational Potential Energy:

1) Object on ground, near a well
2) Object in the well.
Do they both have no GPE, or does the object on the ground still have some GPE (just because the object shown relative to it is actually below ground level, in the well)?

What about objects lying on the floor, but say in a high-rise apartment?
TIA

You have brought up a very good question which highlights the inadequacy of the way science is thought in primary school.

By definition, an object will possess GPE if it has the potential to do work (i.e. to move to the centre of the Earth) due to gravity.

Therefore, as long as an object is not at the centre of the Earth, it possesses GPE.

Unfortunately, primary students are told that an object at the bottom of a slope has zero GPE. The correct term should be \"it has minimum GPE\" as compared to positions above the slope.

In higher study, we usually need to set a \"reference level\" for purpose of calculation. This level is set as \"zero GPE\". However, I believe many students didn't realise that the absolute/actual GPE at the that level is not zero. What they are usually calculating is the \"change in GPE\" and not the actual GPE.

When I was faced with this problem with my kids, I tried my best to explain that for simplicity, we set a certain level for GPE to be zero. That level is up to us. However, the actual GPE there is not zero. I can only pray that they get to understand it later in life.