Part 2 - Finding an object’s weight or volume If an object is NEUTRAL, we can describe what would happen to it. If we were told how many kilograms of positive or negative buoyancy it had, we would be able to calculate the change, more on that later. However, if it is positively buoyant in fresh water it will certainly be positively buoyant in salt water. If an object is negatively buoyant in fresh water we cannot say what would happen to the object if it was moved into salt water. However, if it is negatively buoyant in salt water it will certainly be negatively buoyant in fresh water. If an object is positively buoyant in salt water, we simply cannot say what would happen to the object if it was moved into fresh water. Part 1- Describing what would happen to an object I mark buoyancy questions incorrect more often than any other in the PADI instructor development course than any other type of question. These questions seem to cause more confusion than many others. In general, if we know three of the four things, we should be able to provide the missing fourth piece of information. The current state of the object (floating, sinking or neutral). The volume (or displacement) of the object,Ĥ. There are 4 factors that we need to consider when looking at the buoyancy of an object.Ģ. Put another way, 1 Litre of Salt Water weighs a little bit more than 1kg. That number is 1.03ġ Litre of Salt Water weighs 1.03kg – That’s crucial knowledge. There is one number that we need to calculate the difference.

You need to wear more weight in salt water than when you are diving in fresh water. You probably already know that you are MORE buoyant in salt water than fresh. The difference in the weight of salt water compared to fresh water is what matters here. We have to know what type of water the object is in to answer buoyancy questions. With Buoyancy, the type of water is critical.

Everything we have done to date assumed salt water. I will return to some of the topics addressed in parts 1,2 and 3 to discuss how we would answer them if the question is about FRESH WATER. So far we have basically ignored the type of water. Buoyancy – PADI Instructor Course and Divemaster Exams

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