# Listing all forces on someone swimming in a pool

1. Apr 20, 2006

### sauri

I have this assignment where I am supposed to list all the forces acting on someone who is swimming in a standered olyimpic sized pool.
The obvious force to me was the mass of the swimmer acting downwards and presuming the guy was swimming forward there would be a drag force acting backwards. Also as he is swimming, there will be the force of the water pushing his hands forward. (Action reaction force). This is al the forces I can think of...is there anymore? and am I correct so far?

2. Apr 20, 2006

### Integral

Staff Emeritus
You need something to counter the gravitational force on the swimmer. Why does he stay up?

3. Apr 20, 2006

### pcxmac

how about the viscosity of the water, the forces are man, gravity, water (resistance). The man burns calories, the earth has gravity, and water acts as resistance to man going from one end to the other. I would think it possible to derive more specific forces from those three. buoyancy would be the the difference between man and water, man can drowned though.

4. Apr 21, 2006

### sauri

ok, so to oppose the downward gravitational force we have the upward force provided by the water, which gives us buoyancy. Can we call this the normal force?. So apar from this are there any other force that need to be accounted for?

5. Apr 21, 2006

### gem0688

Have a look at the first picture on this gallery. This may help you solve your problem:

http://wings.avkids.com/Book/Sports/gallery2.html

Hope it helps

x- Gema -x

6. Apr 21, 2006

### Staff: Mentor

Swimming is mostly about lift and drag (in addition to the buoyancy balancing your weight). The force that a fast swimmer generates with their hands is not just "pushing" the water back. It's using your hands as wings or propeller blades, to generate lift. You shape your hands like wings, with the back of your hands rounded a bit. Your pull moves your hand through the water in a path that generates the most lift off your hand (water going over the rounded top of the hand goes faster than under the flatter palm area, generating lift just like a wing).

When you swim fast, the movements of your body in the water up and down and in rotation are very important to optimizing your speed. In butterfly, for example, the better your dolphin kicking motion and body movement up and down, the smoother and faster your overall stroke is. So from a force perspective, you are applying forces to the water with your hands, arms, body, legs and feet that aren't directly for pushing you forward, but are very necessary for a good stroke. Another example is how getting a lot of rotation into your freestyle stroke is important for good medium and long distance speed and endurance.

Also don't forget that you do get a little propulsion from your feet, although mostly the kicking motion is for upper body balance (except for short sprint races). Finally, remember that part of the body is out of the water, so you will get some very small air (drag) forces too.

7. Apr 21, 2006

### sauri

That helps a lot thanks..one other thing though. If we were to fnd the speed of the swimmer, is it still applicable to use the linear equations of motion?

8. Apr 24, 2006

### Staff: Mentor

What do you mean by linear equations of motion? Lift and drag are not linear....

9. Apr 25, 2006

### sauri

Well i was wondering what kind of calculations could be counducted on a swimmer and how they could be resolved?

10. Apr 25, 2006

### Staff: Mentor

Yoiks! That would be a pretty complex set of calculations! Worse than any boat calcs, since the body is moving and changing so much through each stroke.

You need to simplify the heck out of the situation, I would think, before you can do any calculations. The simplest version would be some boat-like body in the water that does not change shape, has some drag, and has some constant means of propulsion (like a rear-facing water jet). The next more complex model would still keep the constant drag body, but model a propeller's hydrodynamics (lift and drag) in the water as the means of propulsion. The next step would be to make the propulsion a mix of pulsed lifts, with changing drags (kind of like the hands and feet produce). The next step would be to modulate the drag to start to simulate the changing body shape with the stroke motion.

Are you using hydrodynamic equations for this motion in the water? Or are you wanting to just use simple F=ma kinds of equations? Are you looking for closed-form equations, or will you be using finite element analysis (FEA) software for the analysis?