What kind of investigations allow for the control of variables

The radiation of the fire causes the saucepan to heat up. the conduction of the saucepan then to distribute the heat over the saucepan and to give heat to the water. the convection of the water distributing the heat within the water, till all the water is boiling

That big glowy thing in the sky is called the sun

How are period and frequency related to each other? dperiod is the reciprocal of frequency.