Was thinking about how bombs work and came up with a question.

A layer of water between two solids can either decrease the friction between the two solids, eg. Machined steel and slip-n-slide. Or it can increase the friction between the two solids eg. Wet newspaper.

What I remembered was that sodium bicarbonate tends to reduce the friction due to water, ditto sodium hydroxide and at least some other alkalis.

But surfactants and acids tend not to reduce the friction much.

Chemically, what is going on here?

mollwollfumble said:

Was thinking about how bombs work and came up with a question.

A layer of water between two solids can either decrease the friction between the two solids, eg. Machined steel and slip-n-slide. Or it can increase the friction between the two solids eg. Wet newspaper.

What I remembered was that sodium bicarbonate tends to reduce the friction due to water, ditto sodium hydroxide and at least some other alkalis.

But surfactants and acids tend not to reduce the friction much.

Chemically, what is going on here?

Well now I would not expect alkalis to reduce the friction between, say, two pieces of metal. I’d expect it to do so with a person on a slip n slide, or other kinds of organic matter, because the alkalis can turn oils and other long chain molecules into soaps.

dv said:

mollwollfumble said:

Was thinking about how bombs work and came up with a question.

A layer of water between two solids can either decrease the friction between the two solids, eg. Machined steel and slip-n-slide. Or it can increase the friction between the two solids eg. Wet newspaper.

What I remembered was that sodium bicarbonate tends to reduce the friction due to water, ditto sodium hydroxide and at least some other alkalis.

But surfactants and acids tend not to reduce the friction much.

Chemically, what is going on here?

Well now I would not expect alkalis to reduce the friction between, say, two pieces of metal. I’d expect it to do so with a person on a slip n slide, or other kinds of organic matter, because the alkalis can turn oils and other long chain molecules into soaps.

That’s a darn good point, dv, I’ve only noticed it with organic matter. What about sodium bicarbonate (= baking soda)?

mollwollfumble said:

dv said:

mollwollfumble said:

Was thinking about how bombs work and came up with a question.

A layer of water between two solids can either decrease the friction between the two solids, eg. Machined steel and slip-n-slide. Or it can increase the friction between the two solids eg. Wet newspaper.

What I remembered was that sodium bicarbonate tends to reduce the friction due to water, ditto sodium hydroxide and at least some other alkalis.

But surfactants and acids tend not to reduce the friction much.

Chemically, what is going on here?

Well now I would not expect alkalis to reduce the friction between, say, two pieces of metal. I’d expect it to do so with a person on a slip n slide, or other kinds of organic matter, because the alkalis can turn oils and other long chain molecules into soaps.

That’s a darn good point, dv, I’ve only noticed it with organic matter. What about sodium bicarbonate (= baking soda)?

Yeah I dunno, that’s one of the thing MZL knows.

mollwollfumble said:

dv said:

Well now I would not expect alkalis to reduce the friction between, say, two pieces of metal. I’d expect it to do so with a person on a slip n slide, or other kinds of organic matter, because the alkalis can turn oils and other long chain molecules into soaps.

That’s a darn good point, dv, I’ve only noticed it with organic matter. What about sodium bicarbonate (= baking soda)?

The same thing? I know baking soda as a buffer rather than an alkali, but checking the web “When you’re mixing baking soda with water, the question is what’s the final pH of bicarbonate (HCO3-) and water (H2O). Here’s the chemical formula:

HCO3- + H2O → H2CO3 + OH-

“See what happens there? Because it’s a stronger base, it tends to create HO-, rather than H3O+. What this means is that when you dissolve sodium bicarbonate in water, the solution tends to be more alkaline.”