Question

An aluminium sphere is dipped into water at $10^\circ C$. The temperature is increased, the force of buoyancy:
A. will increase
B. will decrease
C. will remain constant
D. may increase or decrease depending on the $r$ of the sphere.

Answer 1

A material's density varies with temperature and pressure. Raising the pressure on an object lowers the object's volume and thereby improves its density. By raising its volume, increasing the temperature of a material reduces its density.

Complete step by step answer:
The force that induces objects to float is buoyancy. That is the force that is exerted on an object partially or completely submerged in a stream. The variation in pressure operating on opposite sides of an issue immersed in a stagnant fluid induces buoyancy. It is regarded as the buoyant force too.
The formula for buoyant force is given by,
Buoyant force $= {\rho _f}{V_g}$
Here, ${\rho _f}$ is the density of fluid.
${V_g}$ is the volume of an object submerged.

We know that, density of water goes down with increasing temperature.
Thus, buoyant force goes decreasing with increasing temperature.

So, the correct answer is “Option B”.

Note:
Buoyancy, either upthrust, is an upward force exerted that resists the weight of the object that is partially or completely immersed. In a fluid column, as a consequence of the weight of an overlying fluid, friction rises with volume.
Density is proportional to pressure directly and to temperature indirectly. If pressure rises, with constant temperature, density rises. Conversely, as the temperature increases, the density decreases with continuous pressure.
The sphere of aluminium is made of aluminium or of different alloys of aluminium. Aluminium alloy balls, malleable, ductile and non-magnetic, are preferred where lightweight materials are needed that have good surface finishing or wear resistance.