Fish & Buoyancy

Today let's revise some form 4 topics on  Buoyant Force. In SPM, we learned that buoyant force depends on its volume of water displaced. The larger the volume displaced, the greater the buoyant force. Buoyant force also depends on density of the water, i.e greater water density produce greater buoyant force.

As i told u last time, learning physics will be interesting if u are able to blend its concept with nature & things around u. When i was a kid, i loved to keep fish as a pet and guppy was one of my favorites. Fish is very mobile in water. They are able to swim to the surface, stay in the middle of the water or sink to the bottom.

Ok how they did it.. I mean to float and sink?? Basically fish is able to do it through air filled bag called swim bladder. This bladder has nothing to do with its urine product. In fact swim bladder helps most fish to maintain its  buoyancy. To swim upward a fish fills the bladder with oxygen through the gills. When the bladder is filled with oxygen, the fish has a greater volume and its bladder is expanded. This displace more water and so it experiences a greater buoyant force.

In order to sink,air is removed from the bladder that causes decrease in its volume. Thus its average weight will be greater greater than buoyant force which then pull it towards ocean floor.

To float at certain level, the bladder is filled with air until it displaces a volume of water to produce a buoyant force that equal to its weight. In this case, the weight & buoyant force are in equilibrium. Thus it stays at that level. The same concept is applied in submarine except submarine needs a ballast tank to increase or decrease its buoyancy by adding or removing sea water inside it.

SPM Physics: Archimedes Principle

In  form 4 chapters, there are some important physics principle need to be mastered now b4 its too late. In each principle u must understand and able to do the following:
i.state the principle
ii. relate the factors that affect the principle
iii. understand the experiment (if available)
iv. the calculation part (if available)
iv.describe its application

Among those requirement, most students have been focusing too much on doing calculation. Bila jumpa formula jer,  u guys are keen to do exercise on solving the mathematical problems.In the end u 've ignored one of the most important part, i.e its application. Usually the application part will be asked in the paper 2 either section A, B or C. The application part requires u to explain almost everything on how the things work based on relevant physics concept.

As a continuation from our previous discussion regarding hot air balloon, i want u to recall about its famous physics principle i.e Archimedes Principle. Watch this video for a better understanding about it...





If u've gone through the videos or revised this principle through reference books, make sure that u are able to describe the following applications by relating it to Archimedes principle:
1. submarine
2.hydrometer
3.cargo ship
4.hot air ballon
5.plimsol line and others

U may discuss about it with others in the comment section or the chat box. Enjoy your revision :)
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Archimedes & Hot air Balloon

Ok..today i'm gonna answer my previous question on hot air balloon...some of u did answer it with some common sense on why the balloon rises easily in the early morning..
However in SPM, using common sense only isn't enough for u to get full mark..u must relate your answer with relevant physics concepts or principles.

...Physics concept??? What physics concept???
To make it simple, if hot air balloon rises, it needs a larger force pulls it up  to counter its  weight that pulls it down.
In SPM, this upward force is called buoyant force..atau in bahasa melayu we call it 'daya apungan'.Thats why the balloon can rise & float, coz ada 'force' yang tolong mengapungkannya. So the question is how to have this 'daya apungan' big enough to pull the baskets??

This buoyant force concept comes from a famous principle called 'Archimedes Principle'.Now, lets analyse how can we can relate it to this principle...

Archimedes Principle
Mr Archimedes states that...
If an object is fully / partially immersed in a "FLUID" the buoyant force is equal to the weight of the fluid displaced.


The term 'fluid' is used in the statement above..do u understand what fluid is? Senang cerita fluid ni adalah benda yang mengalir such as liquid & gas. In the case of hot air balloon, the object is the balloon. The fluid is the surrounding air ( udara) which is the one that was displaced.

THEN according to archimedes principle..we can deduce a formula like this:

Buoyant force  = Weight of AIR  displaced  ( since W=mg)
Buoyant force  = mg  [(mass of air displace ) x (g)]
(since density ρ = m / V ,  so m = ρV)

Therefore,
Buoyant force  = ρVg (air displace)
                          ( ρ =density, V =volume)

From the formula, Buoyant force depends on the air density.
We can say that the bigger the density, the larger the buoyant force...
Ok this is the key factor to determine the right time for hot air balloon to take off .
..
Early in the morning, the air is cooler than in the afternoon. Cooler air is denser  than hot air, i.e it has higher density. According to the relationship above, cooler air will result in bigger buoyant force. So the balloon has a larger buayant force to counter its weight. Thus the balloon will be easier taking off in a cool temperature rather than during hot tempperature. This explain why the organiser choose those two session, i.e early in the morning and in the evening.

Another point,when buoyant force is bigger, so we can carry more loads. Thus if the same no of 'burners' is used,more participant can be carried in the morning compared to afternoon.

Please noted this discussion is only concerned about the air density surrounding outside the balloon. 

There are many other factors that allow the balloon to rise faster..so its your task to figure it out yourself  :) 

haha ni ada sikit clue, cuba u all masak maggi, then observe..asap dia naik ke turun :) ????

tapi kalau bukak freezer peti ais cuba tgk asap dia naik ke turun??

May b u can also try this activities at home..

Hot Air Balloon in Putrajaya

Recently i managed to catch a closer look on hot air balloon event which was held in Putrajaya. Unfortunately when my turn was almost there, the lightning flashed and the sky rained on us. Well at that time i would rather stay on the ground rather than risking my life a close encounter with the lightning :).. In the end the organiser had postponed the balloon from taking off .
Here is some of the interesting shots to be shared during the event..

The picture looks interesting rite :)...anyway i have some questions  to all of u. During the event, the organiser allowed spectators to ride the ballon only for these 2 sessions, i.e


i. as early as  8am  to  11am, or
ii. ..from 6pm  to  8pm

Haha..by using relevant physics concept :), can u explain why these two session are chosen? Why can't it be at 12pm, 3pm or 4pm?
Lets share your answer in the comment section..let's see who can give the most accurate answer :)