**Ask a monkey a physics question thread**

[MadMojoMonkey]

What's the difference between an amorphous solid and a non-Newtonian fluid?

You're throwing me softballs, now.

Proof Non-Newtonian fluids are awesome.
This is not in English, but it doesn't matter. They have a decent sized pool of (I'm guessing) oobleck, or cornstarch and water.
Skip to 1:30 for the part where 1 person is submerged in the pool while another is running on the surface.

Making oobleck is a great way to kill an hour with any age group who hasn't played with it before.
I mean ANY age group - from toddlers up to "Am I dead yet?"

I'll talk about the physics in another post.

Is this why ketchup doesn't come out of the bottle?

Ketchup is a normal, Newtonian, viscous fluid.

Viscosity is "resistance to flow" and ketchup has it. It also has surface tension which tends to hold the surface of the fluid in place.
When you try to pour an old-fashioned glass ketchup bottle, especially if it's new, and full, with a smaller surface area, then the viscosity and surface tension teem up to restrict the flow of the ketchup in the small gap.

If you turn the bottle so point downwards and shake it, you have another problem. The whole mass of ketchup wants to move out the opening, but in so attempting, it creates a vacuum pressure behind it, which prevents it from flowing. The viscosity is thick enough to prevent "glugging" for a surface area that small.

If you lay the bottle sideways and give it a gentle back-and-forth wiggle, you can get the surface tension to break, and the ketchup will start to flow. Alternatively, you could just use a knife or any pokey-tool to mark the smooth surface of the ketchup in the bottle, and it would then flow.

If you bang it too hard would the bottle flow as well?
Could the ketchup and bottle form a colloidal suspension?

I think those are possible only if you bang it hard enough to pulverize the glass into sand, but I fear you're trying to trick me.

Is Renton correct that states of matter can appear relatively arbitrary?

Absolutely. There is gray area in this, and Renton is only talking about the 4 most common states of matter. We've not discussed super-critical fluids, or the super-fluid state of Helium, or the semi-fluid behavior of sand.

Atoms bond to each other in some blend of ionic and covalent bonding. It's never purely one or the other. Molecules bond many atoms together, with various strengths of ionic/covalent at each bond. It is the nature of the inter-atomic and inter-molecular bonds that determines the characteristics of a substance, along with temp., pressure, density.