Some brain teaser for the scientific-minded

[motorbiking]

Did you not learn that in science lessons at school?

school?

 

[motorbiking]

9.81m/s2

is that when it comes unstuck?

 

[MNW67]

is that when it comes unstuck?

Not specifically

 

[motorbiking]

Providing the adhesive is applied to the entire surface, it will scale up just fine. The only issue is that if an edge, begins to peel, that can drag the lot down, and so edge support might be needed, until the adhesive drys.

Compare it to wallpapering a ceiling...

A small piece of wallpaper will easily stick to a ceiling, a full length will be more difficult, because the ends will tend to unstick, and once the ends unstick, the lot comes back down.

Yep - size matters:

Pressure-Sensitive Adhesives (PSAs)

The basic concepts, formulations, and test methods of pressure-sensitive adhesives are presented. The importance of interfacial interactions, viscous loss, and extensibility are stressed. The common rheological tests are described and the equivalence of deformation...

link.springer.com

 

[noseall]

Did you not learn that in science lessons at school?

Ahh, gotcha.

When I think of steel pins these days only one comes to mind...

 

[henry1]

Did you not learn that in science lessons at school?

I didn't expect that for pins. I know some spiders can walk on water.
The pin floats because the weight is not enough to break the surface tension. If you put 1000 pins next to each other, I would expect them to float as well as long the surface tension is the same. In reality I suppose the presence of 1000 pins will disturb the surface tension, which is why we don't see a Youtube video of 1000 pins floating.

 

[henry1]

Providing the adhesive is applied to the entire surface, it will scale up just fine. The only issue is that if an edge, begins to peel, that can drag the lot down, and so edge support might be needed, until the adhesive drys.

Compare it to wallpapering a ceiling...

A small piece of wallpaper will easily stick to a ceiling, a full length will be more difficult, because the ends will tend to unstick, and once the ends unstick, the lot comes back down.

Who wallpapers a ceiling?

So the tile can be infinitely large (and heavy) and as long as the adhesive's strength is higher than the force of gravity per unit area, it will always hold?

 

[Harry Bloomfield]

So why do the ends unstick! Another science question. I have no idea.

Two reasons..

1. the edges will have more inclination to curl, and push away from the ceiling.

2. an edge, has less supporting it - no support next to it, versus further towards the centre.

 

[Harry Bloomfield]

I didn't expect that for pins. I know some spiders can walk on water.
The pin floats because the weight is not enough to break the surface tension. If you put 1000 pins next to each other, I would expect them to float as well as long the surface tension is the same. In reality I suppose the presence of 1000 pins will disturb the surface tension, which is why we don't see a Youtube video of 1000 pins floating.

Greasing, oiling, or waxing the pins helps. Dip the pins in soapy water, first, and they will immediately sink in the plain water.

 

[Justin Passing]

If I have an adhesive that holds a 1 cm x 1 cm tile onto the ceiling, will the same adhesive hold a similar tile 2 m x 2 m onto the same ceiling? If not, why not?

Before you say it's heavier, consider that the adhesive is providing the same force per unit area for both tiles, and the force of gravity per unit area for both tiles is also the same...

I asked 2 different AIs this question. One said it was due to imperfections, as if there are no imperfections in the 1 cm x 1 cm tile scenario. The other AI in the end agreed with me because I was relentlessly harassing it!

Yes
unless
the ceiling's not flat.

 

[Harry Bloomfield]

Who wallpapers a ceiling?

Once more common, than now, but people do paper ceilings even now.

 

[MNW67]

In reality I suppose the presence of 1000 pins will disturb the surface tension, which is why we don't see a Youtube video of 1000 pins floating.

It is a complex interaction of surface area and wetting angle. Things I barely remember. If all the pins are touching in one big mass then it will sink. But if there is a sufficient gap between each pin they will float.

 

[Harry Bloomfield]

It is a complex interaction of surface area and wetting angle. Things I barely remember. If all the pins are touching in one big mass then it will sink. But if there is a sufficient gap between each pin they will float.

Is the correct answer! If you imagine the surface tension, as an elastic surface - the elastic will only support a certain weight, in an area, before it fails.

 

[motorbiking]

Surface tension creates a film on the water, the water molecules are attracted to each other. The pin has a greater mass than the displace water, if you dropped the pin in, it would sink, but place it carefully and it floats on the surface tension. The temperature of the water is relevant. It doesn't work with hot water.

 

[Harry Bloomfield]

The temperature of the water is relevant. It doesn't work with hot water.

Hot water landing in the sink, from a tap, makes a very different noise to cold water landing in the sink, due to the surface tension. I make use of the change in noise, when doing the washing up - hot tap on, going to waste, until the noise changes, then swing the spout over the washing up bowl.

The lower surface tension of hot water, itself makes wetting the washing up easier.