if someone is drowning in a pool why can't he pull himself up the surface by pulling on his own hair upwards?

The reason someone cannot pull themselves up to the surface of a pool by pulling on their own hair is due to Newton's Third Law of Motion, which states that for every action, there is an equal and opposite reaction.

Here are the steps to understand this:

1. When you pull your hair upwards while in water, you are applying a force to your hair.
2. According to Newton's Third Law, your hair will also apply an equal and opposite force back onto your hand.
3. This means that the force you are applying to your hair is counteracted by the force your hair is applying to your hand.
4. Therefore, the net force is zero, and you will not move upwards.
5. In addition, your body's buoyancy and the density of the water also play a role in this. Even if you could exert a force by pulling your hair, it would not be enough to overcome the buoyant force exerted by the water, which is pushing you downwards.
6. Lastly, pulling your hair would likely cause pain and could potentially cause injury, which would not be beneficial in a situation where you are trying to save yourself from drowning.

In conclusion, it's physically impossible to pull yourself up to the surface of a pool by pulling on your own hair due to the principles of physics and the properties of water.