Why some almonds float on surface of water while some settle at bottom?
You might have observed, when almonds are soaked in water some of them float on surface of water while some settle at bottom. Why this happens? To understand this you have to understand What is upthrust (buoyancy) force.
Upthrust force (buoyancy):
If you lift a heavy stone by a rope and then dangle it in water you will find it appears to weigh less, this is because of the upthrust of the water on the rock. It is much easier to lift things in a swimming pool – the upthrust of the water helps support them.
If you lift a heavy stone by a rope and then dangle it in water you will find it appears to weigh less, this is because of the upthrust of the water on the rock. It is much easier to lift things in a swimming pool – the upthrust of the water helps support them.
Things float because the pressure of the water underneath them pushes up and supports them; in other words, water pressure (upthrust) pushing upward balances weight (the force of gravity) pulling downward. That's one of the reasons why we swim in a horizontal position: spreading the body flat makes it work more like a raft, so there's more upthrust from the water below.
Upthrust is defined as the upward force on the object provided by the liquid because the object has "displaced" some of the fluid. The volume below the water level that is now occupied by the object used to be filled with water and if the object has a different density than water there will be an upward force on the object. If this force is less than the weight of the object the object will sink.
We can calculate upthrust of any fluid on any object by this formula:
Buoyancy = (ρ)(V)(g) = weight of displaced fluid.
Here ρ is density of fluid, V is volume of object immersed in fluid and g is gravitational acceleration. It is constant. g=9.80665 m/s2 (approx. 10 m/s2).
This is also called principle of floatation and Archimedes principle. Archimedes' principle is named after Archimedes of Syracuse, who first discovered this law in 212 B.C.
Any object, wholly or partially immersed in a fluid, is buoyed up by a force equal to the weight of the fluid displaced by the object.
According to Archimedes principle if an object have greater volume it will accommodate greater upthrust force and if density of fluid increases, it will also cause increase in upthrust force. That’s the reason why a needle sink in water but a ship do not.
Now back to almonds, you might have observed some almonds that are hollow from inside which means they have air inside them, which makes them less dense than other almonds and water. Almonds which are less dense but are same in volume than others, float on the surface of water.
Sources
http://www.explainthatstuff.com/swimming-science.html
