The lonely science post thread

[Chz]

Is there a name for the optical illusion whereby when you are watching a rapidly spinning object, such as the allow wheel of a fast moving car on the lane next to you, or the spinning propellers of an airplane as it increases its RPM, you see a kind of light pattern turning clockwise over the fast spinning object which sometimes seems to decelerate, stop, and start turning in the opposite direction?

It’s not just me seeing it, right?

It's rare(ish) to the naked eye in sunlight, but common enough in recordings or under a flickering light. It's called the "wagon wheel effect". Or temporal aliasing, if you're being all technical.

 

[petee]

pluto apparently

https://i.redd.it/lz1ewpw693t91.jpg

www.reddit.com

 

[two sheds]

Sort of evident but interesting, I thought:

Scientific literacy undermines conspiracy beliefs

New research shows that higher scientific literacy, encompassing knowledge and reasoning, reduces belief in conspiracy theories by improving evidence evaluation.

www.psypost.org

 

[PTK]

I was once holding one of those horns driven by compressed air. You press a button, and this causes the air to leave the cylinder, expand, and pass through the horn, making a noise. The cylinder soon became very cold.

Question: Why did the cylinder become cold?

 

[WouldBe]

I was once holding one of those horns driven by compressed air. You press a button, and this causes the air to leave the cylinder, expand, and pass through the horn, making a noise. The cylinder soon became very cold.

Question: Why did the cylinder become cold?

Evaporation.

 

[2hats]

Adiabatic cooling. The gas molecules move further apart and the energy to facilitate this comes from the surroundings. Some more heavily compressed gases additionally cool due to change of state (the pressurised 'gas' is actually [near-]liquid in the can).

 

[two sheds]

Reverse of why bicycle pump gets hot when you pump air into a tyre. In a fridge or heat pump the compressor heats up as the liquid is compressed and cools down in the evaporator.

 

[PTK]

Adiabatic cooling. The gas molecules move further apart and the energy to facilitate this comes from the surroundings. Some more heavily compressed gases additionally cool due to change of state (the pressurised 'gas' is actually [near-]liquid in the can).

Why do the molecules move apart?

 

[2hats]

They possess kinetic energy (they are not at absolute zero).

 

[PTK]

This is the problem that I have in understanding this.

The molecules of the fluid are moving around in the cylinder. Depressing the button opens a hole through which molecules escape, rather than bouncing off the inner surface of the cylinder. As the escaping molecules are already in motion, why do they require more energy to keep moving, and how do they acquire that energy?

 

[PTK]

I have just realised the answer!
The escaping molecules do not gain energy; the inside of the cylinders loses energy. The fewer molecules bouncing around in the cylinder, then the lower the total energy in the cylinder.

 

[farmerbarleymow]

Why do the molecules move apart?

They hate each other and want to be apart.

 

[PTK]

They hate each other and want to be apart.

Why then don't humans expand?

 

[farmerbarleymow]

I want to have a bath in tartrazine to see what happens.

Common food dye found to make skin and muscle temporarily transparent

Researchers say procedure not yet tested on people could eventually be used to help locate injuries or tumours

www.theguardian.com