Define pressure. Give its SI unit.
The total force applied per unit area is called pressure.
Mathematically,
Pressure (P) = Force (F) / Area (A)
Its SI unit is pascal (Pa).
An iron nail sinks water but floats on mercury. Why?
We all know that the density of mercury is greater than that of water. Also, density ∝ upthrust. So, more upthrust is exerted by mercury than by water. So, an iron nail floats on mercury but sinks on water.