name the following
measure of the effect of weight of air on all objects.
pls answer quickly its urgent.
Answers
Answer:
The real weight is the weight of the object in a vacuum. The apparent weight is the weight of the object when partially or totally immersed in a fluid e.g. air or water. (And before anyone tries to correct me, a fluid is something that flows; i.e a liquid or a gas.)
Apparent weight = weight in a vacuum - upthrust
In order to understand this, we need a bit of physics and a bit of maths.
I’ll keep things simple by considering a cube with the upper and lower faces horizontal. You don’t have to, but the maths gets very messy if you consider a complex object … and the result is the same. This is a simple analysis that a Y10 or Y11 student can understand.
The physics we need is that P = F/A; pressure is force divided by area. You can rearrange this formula to give
F = P x A.
The second bit of physics we need is to know that the pressure in a liquid increases with depth. Pressure due to the weight of a liquid of constant density is given by:
P=ρgh
where
P is the pressure,
h is the depth of the liquid,
ρ is the density of the liquid, and
g is the acceleration due to gravity.
(Some people might now be getting worried that we are mixing up vectors and scalars willy-nilly. For now, please just take my word that it’s OK.)
WE can combine these two equations to get
F = =ρghA
We can shift things around a little to make that
F = =ρgAh
and realise that, for a cube, Ah = the volume, V, so it becomes:
F = =ρgV and this is the weight of the fluid displaced.
Now the only problem is to understand which direction this force acts. Well, it acts upwards because the force on the lower face of the cube is greater because of the greater depth. We call this the upthrust.
Since the density of water is greater than the density of air, the upward force is greater. And because of this, the apparent weight is less.
Note, we don’t normally consider the variation of air pressure with height. That’s because the air pressure at the ceiling of a room is pretty much the same as the air pressure at floor level. But the physics is the same. To make life simpler, we consider that the actual weight of an object is equal to its weight in air.