Q&A - P3 Science

[tianzhu]

JayneLL:

could you let me know where you get these questions.

Hi

This question may be from Toanan Science SA2 2009.

Please go to page 7 of this link to see Q8.
http://www.orlesson.org/orp/09Sc/P4-09-Sc-SA2-TaoNan.pdf

Best wishes

[atutor2001]

match3frog:

A picture showing 3 plastic bags tied at the top. Bag A is the smallest in size, Bag B is bigger than Bag A and Bag C is the biggest.

3) The mass of air in B is bigger than that in A and smaller than that in C

Can I know why the 3rd answer if not true? Won't a bigger bag contain more air and therefore has a bigger mass than a smaller one?

Thanks!

Hi match3frog

I always visualise air as tiny little dots (molecules) floating about. Its volume depends on the space given for these dots to wander about. The volume of \"1 dot of air\" place in a 10 cu cm tube is considered to have a volume of 10 cu cm. \"1000 dots of air\" in a 5 cu cm tube is considered to have a volume of 5 cu cm. But the mass of 1000 dots of air is definitely more than 1 dot of air although its volume is smaller (as it is placed in a smaller tube). Therefore, we cannot judge whether which bag of air is heavier by looking at the volume alone.

[match3frog]

Dear elkniwt, tianzhu & atutor2001,


Thank you all for the clear and concise explanations!

[peggy]

Can anyone help with this P4 qtn ?


John was running around the field during recess before his teacher brought the class into an air-conditioned room. He felt cold after he entered the room.

A) Explain why John felt cold in the air conditioned room.
B) There are air spaces in a woollen jacket.
When John put on his jacket, he felt warm. Explain how the jacket had kept John warm.


Many thanks in advance !

[iFruit]

peggy:

Can anyone help with this P4 qtn ?


John was running around the field during recess before his teacher brought the class into an air-conditioned room. He felt cold after he entered the room.

A) Explain why John felt cold in the air conditioned room.
B) There are air spaces in a woollen jacket.
When John put on his jacket, he felt warm. Explain how the jacket had kept John warm.


Many thanks in advance !

1) Heat transfers/travels from Johns body to the surrounding cold air and hence he feels cold.

2) Wool is a poor conductor of heat so the air spaces in the jacket retain the heat keeping John warm.

HTH

[Laurenwkids]

tianzhu:

JayneLL:

could you let me know where you get these questions.

Hi

This question may be from Toanan Science SA2 2009.

Please go to page 7 of this link to see Q8.
http://www.orlesson.org/orp/09Sc/P4-09-Sc-SA2-TaoNan.pdf

Best wishes

Thanks Tianzhu for the link. I was :? when I saw the question.
Got to read up more to help my daughter.

[tianzhu]

peggy:

Can anyone help with this P4 qtn ?


John was running around the field during recess before his teacher brought the class into an air-conditioned room. He felt cold after he entered the room.

A) Explain why John felt cold in the air conditioned room.
B) There are air spaces in a woollen jacket.
When John put on his jacket, he felt warm. Explain how the jacket had kept John warm.

Hi

In this question, we are given a situation with John running around the field during recess. He was then brought to an air-conditioned classroom.

Therefore, it’s important to give answers that connect to the situation in the question.

Under the topic of heat in P4, students learned that heat always flows from a hotter to a colder place or object.

Some thoughts that may be helpful in answering this question.

(a)Exercising ----- higher body temperature ------ heat lost from body to cooler surroundings ----- John felt colder.

(b)Body warm the air near it ----- a layer of air is trapped by the woolen jacket ----- woolen jacket with air spaces ----- a poor conductor of heat -------reduce heat loss ----- keeps John warm

Best wishes

[tianzhu]

Laurenwkids:

Thanks Tianzhu for the link.

Hi

You're welcome.

Best wishes

[peggy]

Thanks Tianzhu. Very well explained.

[atutor2001]

peggy:

Can anyone help with this P4 qtn ?


John was running around the field during recess before his teacher brought the class into an air-conditioned room. He felt cold after he entered the room.

A) Explain why John felt cold in the air conditioned room.

The key point to note in this question is that he was running around before going into the air-con room, i.e. he is hot with perspiration.


In the air-con room, he will feel colder when he is hot & wet than if he is dry. The reason for feeling colder are :

1. The difference in his body temp and the surrounding temperature increases causing the body to lose heat faster.

(second reason - not in syllabus but sometimes tested)
2. The perspiration on his body evaporates faster in an air-con room because the humidity is lower (air-con remove water vapour in the air). Faster evaporation means heat is lost by the body to the sweat at a faster rate i.e. feeling colder.


In my opinion, the most kiasu answer will be :

Running causes his body temperature to increase while the air-conditioner causes the room temperature to decrease. Therefore, the difference in temperature between his body and the surrounding air increases causing his body to lose heat at a faster rate which is why he feels cold.

(the underlined words should be what the marker is looking for)