Question

While making tea or something on a gas stove in a metal beaker . Why don't the metal beaker don't expand because of heat?

Answer 1

It is because this heat is not enough for the metal to expand it will only expand at higher temperatures
It depends on the expansion coefficient of the metal which is a material specific property.

The expansion in length is proportional to the product of the thermal expansion coefficient (K) with the temperature gradient. Therefore if the material expansion coefficient is not same inspite of the temperature gradient remaining same the material will expand unequally.