Hello all,
Today's blog is divided in two parts-
1.Secondary Level.
2.Senior Secondary Level.
As the title suggests an iron needle sinks but ship floats.We are going to discuss the reasons in two different levels targeted at two different groups of students.
Talking about secondary level,all the students of class 7th or 8th must have witnessed this question in their science books right.As far as my case is concerned I was in class 8th when this case was discussed in science book in very small part.The reason given for floating of ship and sinking of iron needle made of same material was explained to be related to density.Since iron needle had greater density than water itself so it sank whereas ship floated being less in density compared to water.Thats it.It was supposed to be the answer of 2marks.Then I moved to 9th standard and all of a sudden my father and brother both asked me to answer the same question as they knew in class9th there is mechanics,so they wanted to test me.I replied the same as mentioned above(about density).Both of them were not satisfied with my answer and told me to learn Archimedes's principle and find the correct answer.I was in a state of dilemma that the answer that gave me 2 marks in standard 8th is all of a sudden challenged in 9th.Then I learnt about Archimedes's principle and cleared my paper accordingly.But frankly speaking at this stage also I was confused.
Now come to senior secondary level,here I got to learn about Archimedes's principle in detail and stuffs like bouyancy,centre of mass etc.Now let me quote what Archimedes's principle states-'It states that any body partially or completely immersed in water will experience an upward thrust(buoyant force) which is equal to the weight of water displaced by the body.'Now for an object to float the buoyant force must be equal to or greater than weight of water displaced by the object or else it will sink.The reason why an iron needle sinks and ship floats is that the needle is unable to displace that volume of water whose weight is equal to needle or greater than needle.See the funda is very simple you take a 50Newton needle which displaces 20N water,then buoyant force be also 20Newton but 50Newton acting downwards and 20Newton upwards,obviously the needle will sink(as per mechanics of equilibrium).So far so good.Now you need to understand the primary force and secondary force.As it is said no action no reaction.Here the object's weight is primary force,weight of water displaced is secondary force and buoyant force is reactive force.Thus to keep the object floating,design of the object should be such that it displaces equal or greater weight of water so that in reaction buoyant force is equal or greater than object's weight to keep the object floating.Naval Architects design ship keeping in mind the above factor.I hope it's clear now.Always try to understand definition,it will help you in critical thinking.
Thanks...
Today's blog is divided in two parts-
1.Secondary Level.
2.Senior Secondary Level.
As the title suggests an iron needle sinks but ship floats.We are going to discuss the reasons in two different levels targeted at two different groups of students.
Talking about secondary level,all the students of class 7th or 8th must have witnessed this question in their science books right.As far as my case is concerned I was in class 8th when this case was discussed in science book in very small part.The reason given for floating of ship and sinking of iron needle made of same material was explained to be related to density.Since iron needle had greater density than water itself so it sank whereas ship floated being less in density compared to water.Thats it.It was supposed to be the answer of 2marks.Then I moved to 9th standard and all of a sudden my father and brother both asked me to answer the same question as they knew in class9th there is mechanics,so they wanted to test me.I replied the same as mentioned above(about density).Both of them were not satisfied with my answer and told me to learn Archimedes's principle and find the correct answer.I was in a state of dilemma that the answer that gave me 2 marks in standard 8th is all of a sudden challenged in 9th.Then I learnt about Archimedes's principle and cleared my paper accordingly.But frankly speaking at this stage also I was confused.
Now come to senior secondary level,here I got to learn about Archimedes's principle in detail and stuffs like bouyancy,centre of mass etc.Now let me quote what Archimedes's principle states-'It states that any body partially or completely immersed in water will experience an upward thrust(buoyant force) which is equal to the weight of water displaced by the body.'Now for an object to float the buoyant force must be equal to or greater than weight of water displaced by the object or else it will sink.The reason why an iron needle sinks and ship floats is that the needle is unable to displace that volume of water whose weight is equal to needle or greater than needle.See the funda is very simple you take a 50Newton needle which displaces 20N water,then buoyant force be also 20Newton but 50Newton acting downwards and 20Newton upwards,obviously the needle will sink(as per mechanics of equilibrium).So far so good.Now you need to understand the primary force and secondary force.As it is said no action no reaction.Here the object's weight is primary force,weight of water displaced is secondary force and buoyant force is reactive force.Thus to keep the object floating,design of the object should be such that it displaces equal or greater weight of water so that in reaction buoyant force is equal or greater than object's weight to keep the object floating.Naval Architects design ship keeping in mind the above factor.I hope it's clear now.Always try to understand definition,it will help you in critical thinking.
Thanks...
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