Frequently asked intresting facts - 3

When you don't know swimming your body will drowned into water but when you are dead your body floats on the surface? 

A body will float when the weight of the body is less than the weight of the fluids it displaces.

When a body start to drown in water firstly the air in the lungs is replaced by the water and hence density of the body is much more than density of water therefore firstly the body sinks. 

But after sinking the bacteria in the body start decomposing the body due to which gasses like methane, carbon-dioxide are released due to which body starts to bloat or swells up and increases in the volume so that average density of body decreases and now it can displace more water, as density of body became less than water now body start to floats on surface. This happens approximately after 24 hours of drowning.

High speed wind tends to lift the roof why?
Hey guys before understand this first go through the relation between pressure and velocity which is mentioned in my Lecture - 10. Now after this I am assuming that all of you guys know when velocity of particles increases they creates a low pressure zone.
When the kinetic energy of air above the roof is high than it creates a low pressure zone or we can say that the pressure present above the roof became low, which creates a sucking effect above the roof top.
On the other hand air inside the house is static and hence the static pressure inside the house is more. And hence strong winds creates the high pressure difference which generates lift force and causing the house roof to fly off.