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"Physics Question: How slippery is sand?" Topic

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altfritz03 Aug 2020 6:36 a.m. PST

Assume you are intrepid archaeologist Indiana Jones and you have come across a lost tomb entrance hidden in a cleft in some rock outcrop. It is an open entrance with stairs descending into the darkness. Over time sand and rocks and other debris has blown or fallen into the entrance and is scattered all over the stairs.

Question: How stable is your footing? Are you liable to slip and slide down the stairs?

Lucius03 Aug 2020 7:55 a.m. PST

In true war-gamer fashion, the answer is that it depends what KIND of sand it is. I remember reading a book about a guy on a British commando team who repeatedly risked his life to bring back sand samples from various parts of the Normandy coast, because there were some beaches on which the footing was too unstable.

So, roll a D6, and pray it isn't a "1" . . .

Frederick Supporting Member of TMP03 Aug 2020 7:56 a.m. PST

It depends on a few things

If the sand was wet and a bit compacted then it may not be slippery at all

If very dry, certainly could be – also depends on the depth of the stairs. Having walked up and down the Great Pyramid of the Sun I would say that Mayans must have had small feet; I had to walk sideways to avoid falling down

Personal logo Editor in Chief Bill The Editor of TMP Fezian03 Aug 2020 8:25 a.m. PST

Can't imagine Indy sliding down the stairs. grin

whitphoto Supporting Member of TMP03 Aug 2020 9:08 a.m. PST

Can't imagine Indy sliding down the stairs. grin

Yeah. And Indy would never ride bit….. eeeerr….. 'tandem' on a motorcycle either….

Personal logo Grelber Supporting Member of TMP03 Aug 2020 11:41 a.m. PST

A line from The Fellowship of the Ring that always seemed odd to me describes Legolas running across the mountain snow: "Then swift as a runner over firm sand he shot away."
This never quite matched my experience with sand on hard surfaces, which would give you a very unsure footing. I assume that JRRT knew whereof he spoke, and may even have been thinking of some classical or Medieval source.
Which seems to mean I agree with Lucius: "It depends."


altfritz03 Aug 2020 1:31 p.m. PST

Well, people race motorcycles and cars – and achieve speed records – on stretches of beach so presumably it is firm. We're talking desert sand, however.

thosmoss03 Aug 2020 1:57 p.m. PST

Also consider the stairs – softer stone,worn by hundreds of slaves marching up and down the flights? A slight dip downward might help the water drain, but it could make a dangerous ramp if it was sandy.

Thresher01 Supporting Member of TMP03 Aug 2020 2:08 p.m. PST

Sand on stairs and rocks can be rather dicey.

Very different than sand on sand.

Sgt Slag03 Aug 2020 2:12 p.m. PST

In tropical Minnesota, we often throw sand on top of snow and ice, to gain traction with our rubber tires. We do the same thing for foot traction, with our shoes, in the downtown areas' sidewalks -- prevents slipping/falling to a very great extent. On bare concrete, it is somewhat slippery, but not too bad -- nothing like rubber/plastic soled shoes on ice; on ice, it is a life-saver, providing critical traction.

Visited Corpus Christi, TX, around 16 years ago, walked, and drove, on the beach: the sand was hard, compacted, and similar to driving/walking on concrete! I knelt down to look at the marks we left in the sand: none, with our rented 15 passenger van. A huge front-end loader drove by, scooping up garbage washed ashore. I looked at his tracks (4-foot tall rubber tires!), and he only left very slight marks in the top surface of the beach sand. Never seen anything like it before, or since. Cheers!

Zephyr103 Aug 2020 2:37 p.m. PST

If the sub-surface is hard, and the sand is thin and dry, it would almost be like walking on a floor covered with marbles, you are going to skid pretty good…! ;-)

Acronim03 Aug 2020 2:58 p.m. PST

The sand does not slip, as abrasive it is, it tends to give grip. Historically, it has been used precisely to provide a firm, dry, and at the same time relatively soft surface; in the Roman circus, in the bullrings … Only when the layer of sand is very very thin and the bottom surface hard can be slippery, although you can hardly slip enough to make you fall. However, the antlion uses the sand as a trap, but not because it slips, but because it collapses.

In summary and answering the question; Indy doesn't go downstairs, roll the whip onto a ledge and jump.

Personal logo etotheipi Sponsoring Member of TMP05 Aug 2020 2:16 p.m. PST

you can hardly slip enough to make you fall

To quote the kids of today, "You don't know me!" :)

To the OP, I would think stair subjected to centuries of sand and wind would become a ramp.

Personal logo Narratio Supporting Member of TMP06 Aug 2020 11:56 p.m. PST

Another with "It depends". The sand we use in construction is angular and gritty, the particles are quite large with lots of edges. This helps it link together to create a semi stable surface. The particles of sand you find in children's play pits are smaller, more rounded so can be dug up and moved around, you use water to join it together but, once dried out, it flakes away very easily. The sand particles found on the tops of sand dunes or blowing across dried lake beds are almost round and quite small, it really is slippery stuff. You can't use it to make concrete, the resultant stuff just collapse.

So yeah, it depends.

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