We're all probably a little too familiar with the frustrations of trying to get ketchup and chili sauce out of a glass bottle
Unfortunately, slapping the bottom of the bottle to get the sauce out has only two possible results: You get nothing, or you get a sauce avalanche. There's no in-between.
Turns out we've been doing it all wrong! Holding your bottle straight-down and hitting the bottom won't actually make the sauce come out. In fact, it forces the sauce back inside the bottle.
In order for the sauce to flow out of the bottle, air has to squeeze in on one side of the bottle's neck. Also, ketchup and chili sauce have the unusual condition of being both solid and liquid, which means they respond to different Newtonian laws.
According to a TED-Ed video by George Zaidan, their thickness and viscosity change based on how long, how hard and how fast you push. When you hit and shake the bottle gently, the sauce behaves like solid and remains in the bottle. When you hit the bottle hard and vigorously, the spherical particles break down and flow too easily out of the bottle, resulting in all that messy glob on your food.
There's actually a perfectly simple way to get your sauce out of the bottle according to the amount you want! All you need to do is hold your bottle at an angle and tap the neck area.
And voilà - perfect amount every time!