PADI IDC Theory - Physics

Test yourself with these questions

PADI Dive Theory - Physics

I’ve met loads of people who tell me that they’re hopeless when it comes to Physics.  

Does that sound like you? 

In a moment, I’ve got a few physics practice questions for you to try out. 

But for now, let’s find out what you DO know about physics. 

It’s easier than you think!

You already know a lot about physics

You know that you breathe more air the deeper you go. 

Balloons get smaller and so does the effect of the gas that you breathe.

Oxygen can become harmful, and Nitrogen can become narcotic. 

You already know this stuff. 

It’s physics. But it’s just diving too. PADI IDC Theory physics isn’t too difficult! 

PADI IDC Theory Physics

Ok, let’s take things one step at a time.
Here we’ll talk about THREE major topics that come up time and time again on PADI Physics exams.

1. Calculating Pressure

2. The Effects of Pressure

3. Displacement

In each of the areas, I’ll give a few tips, and show you a video.

Then you’ll get a chance to answer some questions.

Each of the videos are from my Online Preparation Course. 

You can watch the video first, or you can steam straight into the questions. 

Good luck! 

1. Calculating pressures underwater

The Basics

Being able to calculate pressures  in seawater is essential.

Without this knowledge, you’ll  struggle with some PADI Physics exam questions.

Like where they ask you what size a balloon will be when you take it to 30 metres / 99 feet.

The good news is that it’s easy! 

How it's done

For every 10 metres or 33 feet, the water (or gauge) pressure changes by 1 atm.
The total pressure at depth includes both gauge and atmospheric pressure. 
So, pressure at 10 metres or 33 feet = 1 atm for the gauge pressure, and 1 atm = 2 atm.  

This might help

For every one metre in sea water, pressure changes by 0.1 atm. Example: at 23 metres pressure is: 23 X 0.1 = 2.3 atm for gauge, +1 = 3.3 for absolute. 
For every foot of sea water, pressure changes by 0.0303 atm. Example at 76 feet pressure is 76 X 0.0303 = 2.3 atm for gauge + 1 = 3.3 for absolute
Fresh Water
In fresh water, it’s much the same, but for metric use 0.097 for every metre, and in imperial use 0.0294 for every foot.Effe

PADI IDC Revision - Physics - Pressures Underwater

OK, let’s test yourself with these questions.  

PADI IDC Exam Questions

How did you get on? Check out this video for lots more information

2. PADI IDC Theory: Physics - Effects of Pressure

Let’s move on to Effects of Pressure.

These ones are so important. 
Usually PADI Physics exams have over more questions about the effects of pressure than any other subject. 

You can go straight to the questions or take a look at this first. 

The Basics

These questions usually make up around 40% to 50% of all PADI IDC Physics exams. Anything to do with  changes at depth: Balloons, Breathing rate, Density, Partial Pressure of gasses, How much air needs to be pumped from the surface etc.  

How it's done

Watch the video to get a really good tip on how to work these out!  
As you get deeper, some things get smaller (e.g volumes)  and some things get larger (e.g.density, breathing rates) 
First, work out whether the answer will be larger or smaller. That will tell you whether you’ll multiply or divide. 

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PADI IDC Exam Physics Effects of Pressure Questions

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3. PADI IDC Revision - Physics - displacement

Now we’ll move on to the displacement topic. 

This is the Archimedes principle, where back in ancient Greek times He stated: a body immersed in a fluid experiences an upthrust equal to the weight of the fluid displaced.

Which simply means that if you jumped into the sea, with all your kit on, water would be displaced. 
Now, IF the weight of that displaced water weighed the same as you – well, you’d be in luck! because that would mean that you’d be neutrally buoyant! 

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The Basics

his subject is much simpler than some instructors make it out to be. 
Take a look at the video with an open mind and you’ll be surprised at how easy it is.  

How it's done

In fresh water, it’s often as simple as taking one number (displaced water) from another (weight). 
In salt water, first divide the weight by 1.03, and then go ahead as with fresh.
Multiply the cubic feet of displaced water by 62.4 in fresh water, or 64 in sea water, then deduct that number from the weight of the object. Divide that number by either 62.4 or 64 depending on fresh or sea to get the answer in cubic feet.

Now we move onto the displacement questions. Make sure that you read the question! 
Check if it’s in salt or fresh water!

PADI IDC Exam Questions

How did you get on?

Don’t worry if you got a bit confused with these questions. They’ll become clearer with practice. 

The more that you practice, the more you’ll understand and the more confident you’ll get. 

Mock IDC Theory Exam papers

If you enjoyed answering these questions, you could answer a LOT MORE! 

Click the link to find a whole load of Replica Mock PADI IDC Exam Papers.
For both Theory and Standards.

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PADI Revision - skills and environment