Can someone explain Happy Quinn jokes in the Scorpion episode "Crazy Train"?

Basic puns, word-play jokes, based on math, chemistry, and physics.

Knock, knock! Who's there? Matthew. Matthew who? "Math-you" could never do unless you had an IQ of 184.

Math is hard. Unless your really smart.

Ammonia and sodium hypochlorite hook up at a bar. Everyone inside dies.

Sodium Hypochlorite is in most houses. It's called Chlorine Bleach. Mix it with Ammonia and you get Chlorine Gas. And Die. (For real, it's dangerous. Says so right on the bottle. Also don't mix Chlorine with Vinegar or basically any other cleaner. It's dangerous to clean a house right!)

I've been reading this great book on antigravity. I can't put it down.

Gravity, putting things down, I get it. It's a double entendre.

I have this new theory on inertia, but it's not gaining any momentum.

Inertia and Momentum are two basic properties of an object. An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force. as stated in Newton's First Law of Motion. Inertia is what keeps things not moving, from not moving, unless you add energy (I.E. Momentum). Here's Newton's First Law for Dummies.