We know that Density is equal to the mass of the object divided by the volume of the object. But how does this formula tells us about our every day experience like why cruise can float on the water even though it’s very heavy, why iceberg floats in water and not fully submerged? If you ever wear a life vest or jacket before going out to water activities like canoeing, wind surfing and wakeboarding, you will notice that you can float in the sea water when you have it on. However, without it, you will find that it is harder to float in the water! Intuitively, adding more additional materials onto our body should make us sink into the water but why with life vest, it is the opposite? Take a few minutes to think…
Well, it depends on what kinds of materials you are carrying. Strictly speaking, it is the density of the material that makes the different. Let’s take the life vest as an example. By wearing the life vest, you are actually increasing the volume of your body size. If you have ever held a life vest before, you will find that it is quite light in weight. A light weight life vest means that it's mass is small too, since from W = mg, we know that weight of the object is proportional to the mass of the object as the gravitational field strength is assumed to be
10 N/kg (constant) on earth. As Density = Mass/Volume, small mass divided by a BIG VOLUME (body + life vest) will give you a small density value. That’s why you could float much easier in sea water if you have a life vest on. Could you imagine what will happen if you wear a life vest made of metal? You could try this by finding any piece of metal and place it into water, but please don’t try wearing one of this life vest (if it’s available), as you could probably guess what will happen to you…
The web-link below will show you a video on how density is an important consideration for a scuba diver to submerge in a swimming pool water and sea water. Will the scuba diver sink into the water in the same way for both water conditions? Make a guess and find out from this video to see if you are right…
For more exploration on density and buoyancy, refer to this video from YouTube...
31.
ReplyDeleteGreat.
i thought i knew all about density.
but nevertheless, i learnt something new through the video:D
36. The video is a little confusing in the starting but as i view for a few time i slowly understood yay;)
ReplyDelete6. i learnt alot more on density, mass and volume after reading this post. i learnt bout the factors affecting density
ReplyDelete9. hehe, wow. I knew about the life vest thing but i never thought that it could be linked to this...
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ReplyDeletehahas. i think the video is real interesting..like how they use a huge cruise ship to tell us that whether an object floats or sinks does not depend on its weight but its density. cool...
Oh most parts of it we learnt last year, but I didn't know anything about the lifevest thingy.
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23. Interesting how these theories go beyond simple school examinations...
ReplyDeleteI learned that a possessing a body of larger volume, coupled with a small mass = small density value, derivable from the equation of density which is Mass/Volume.
Thanks.
19 says wow!Now i learnt more about the practical applications of Mass and Density.All the while we were learning the thoery part of it.Thanks Mr Koh.Maybe next time you can include practical applications with every physics topics to make it more interesting.
ReplyDelete4. Wow! It is very interesting. It also shows us that physics is not a subject that we study just to pass exams and when we start working, we can thrash it aside. It is actually a very useful subject which can help us in our everyday life. The life vest was a great example to learn about density. small mass divided by a big volume (body + life vest) will give you a small density value.
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ReplyDeleteohh! there are so many factors that affect density, i did'n know some of them until now!=]
5. Yeah, we learnt about most last year, but i understand everything better now, and im clear about the live vest thing. however, im quite mixed up sometimes about which thing is denser and less dense. im always mixing them up.
ReplyDelete16:the video's explanations were quite clear and easy for me to understand and the examples shown like the cruise ship and hot air balloon were interesting.
ReplyDelete7.oh i didn't know that density help us a lot in our everyday life.I did not get a better understanding until I see the video,it is very interesting as it tell us how important is density and how it is applied to our surrounding things.
ReplyDeleteI think I learnt something from here instead- that there are factors that affect density..
ReplyDelete30-i learn more about density.and the examples are interesting
ReplyDelete3. I learn more about density, mass and volume.
ReplyDeleteI didn't really understand the topic, but now i understand(:
18: This topic is very useful for daily application (:
ReplyDelete10. I think density this topic is very interesting, and the applications are very fun!
ReplyDelete27.
ReplyDeleteoh yea nice video it was also very helpful
27.
ReplyDeletei didn't know bout the lifevest thing xD