Why does water boil harder when you push a ladle to the bottom of the pot? I noticed this today while cooking. When I push a ladle to the bottom of my pot on my stove top, the boiling sound gets louder, and the bubbles rise to the top more aggressively. Can someone explain? 
 A: I see this effect on my electric stovetop.  The bottoms of my pots are no longer quite flat, and pushing downward on the pot improves the thermal contact between the pot and the heating element.  The effect is present whether I push down on the bottom of the pot with a ladle, or whether I push down on the handles on the outside of the pot.
On a gas stovetop, where the heat transfer is by convection, pushing down on the pot doesn't change the thermal conductivity between the pot and the heat source and so doesn't cause any change in the rate of boiling.
A: There’s either one or two factors at play, depending on what, “… push my ladle to the bottom of my pot…” means.
If you were pushing the ladle hard on a wonky old electric coil stove, then it could be what someone else eluded to: the force pushing down on the pot can effect how much of the pot is in direct contact with the heating element, more direct contact equates to more/quicker heat transfer, and lastly, better heat transfer equates to a stronger boil.
If you were not pushing the ladle down hard on the bottom of the pot (or you don’t have a wonky old electric coil stove), you could still notice the boil getting stronger if you depress something large enough deeper into the water. Obviously, it takes more time to get a pot full of water to boil, than a pot with just an inch of water.  By pushing something into the pot, you are displacing some of the water farther away from the heat source. Less water getting more direct heat will change it’s state of matter faster (boiling is just H2O going from a liquid to a gaseous water vapor) which makes the whole pot look like it’s boiling harder.
