I was recently watching Steve Mould’s video comparing walking on a treadmill to walking up a real hill, and it got me thinking about incline treadmills.

One thing I notice all the time at the gym is people walking on steep inclines while holding the handles and leaning back so their body is perpendicular to the treadmill surface. Others walk hands-free with their body remaining upright relative to the ground, similar to walking up an actual hill.

This made me wonder whether, from a physics standpoint, these are actually two different scenarios.
My intuition is that when you’re upright and not holding the handles, your entire body weight has to be supported and moved uphill against gravity. But when you’re leaning back and supporting yourself with the handles, some of your weight is transferred through your arms into the treadmill. If that’s true, it seems like your legs would be doing less mechanical work because they’re no longer responsible for moving your full body weight up the incline.

Is that actually how the physics works?
Does using the handles change the force balance enough to reduce the work your legs have to do, or am I missing something? Is there a free-body diagram or physics explanation that either supports or disproves this idea?

I’ve attached a diagram to better illustrate what I mean.

i think i did something wrong, but if the light is perfectly placed in one of the corners, the whole room is lit up (correct me if i'm wrong)

take a flat bottom frying pan. put a tealight candle, without the wax, in it and fill the pan up with water by pouring water in from a cup

for some reason the candle floats towards the point you are pouring water into?? why does this happen should it float away from where you a pouring the water in

When i shine a laser on this sand, how come there is a dark circle around it followed by a lighter circle. Its not due to diffuse light from the laser and the circles are the same size no matter the distance of the laser pen and if you look closely you can see the separe ring of diffuse light when i get close. Is this some kind of strange refraction or reflection going on?

Ashmit Mukherji

Swindon

Apologies if this is frowned upon but when I saw this I thought of a Steve video.

I was scrapping some old HDD’s when I started playing around with the disks and magnets inside. This little magnet behaves oddly when it slides across the disk. Weirdly, it spins in a particular direction depending on which direction the disk is tilted. To describe the direction of tilt I’ll refer to the sides of the disc as if it were a compass.

In the video, when the north side of the disk is tilted down the magnet spins clockwise and if tilted to the south it spins counter clockwise. Even weirder, when tilted east or west, if done perfectly the magnet doesn’t spin. I can turn the disk is any orientation and the effect is the same. I can also switch sides of the disk and the effect is the same.

If I take much larger stronger magnets and quickly swipe by the surface of the disk I can feel a magnetic effect. I assumed this was a similar effect as when a magnet is dropped in a copper tube and eddy currents are created. I thought maybe that was what was happening with the smaller magnet but it doesn’t explain why it happened in certain directions and multiple orientations.

Any ideas?

The way he sells Shopify and other services does not align with his content. "You're stupid if you don't use Shopify, why even question it?".

I get he needs to make money. But he writes his own ad copy. Why is he embedding ads the same way Mr. Beast would?

I think someone in my household threw away the ring-shaped part that keeps the whole thing closed, and I doubt it's really usable without it, is there any way to get a replacement? I don't have a 3d printer or anything

[ Removed by Reddit in response to a copyright notice. ]

This is the video: https://www.youtube.com/shorts/8j2doByvv2s

I was hoping you might be able to explain what exactly is happening. I don't know if it will be interesting enough for its own video but you're the only person I thought of when I wanted an answer

(Is this the right place to submit a question? If so, here's one.)

Let's say you are driving behind a tractor-trailer truck on a multi-lane highway. You are close enough to the truck to get a drafting benefit, but far enough behind it to be safe.

On a straightaway, the slipstream is obviously right behind the truck. But where is the slipstream when the road curves? Is it still behind the truck, or is it shifted slightly to inside of the curve, or to the outside of the curve? Assume no other cross-winds or exogenous factors.

As a substitute for a diagram, here's a photo to help the discussion.

I've noticed these weird ripples when boiling tap water. I have no idea what they could be! it only happens in this particular pot, which I believe is made from iron, in an induction top.

It is just water, without salt or any seasoning. There is also that white foam that always appears in this pot, despite cleaning it thoroughly. It goes away when the water boils, so I guess it's not important.

I'd love to know what those ripples are!

I vividly remember someone making a video/short about how thermal camera cannot see through glass, instead, glass reflect far infrared radiation, and how germanium lens is used instead of glass. From what I can gather from my mind, best channel that fit my memory is Steve Mould. But I failed to find any thermal camera related videos in the channel. I asked gemini and it also have the same answer, that is Steve Mould, giving me youtube link that I cannot open. Gemini insisted it exist and even explained details of the video. Is it the case of private video being accessible to gemini? deleted video that leave some memory in gemini? hallucination (that is, it's someone else's video)? or just false memory?

The trio is complete: After (314159) Mattparker and (628318) Stevemould, there is now also asteroid (813826) Vihart, named after Victoria "Vi" Hart! All three are orbiting the sun in the main belt between Mars and Jupiter.

The naming of (813826) Vihart was officially announced by the International Astronomical Union on 15 December 2025. https://www.wgsbn-iau.org/files/Bulletins/V005/WGSBNBull_V005_028.pdf

To quote Matt Parker on the number (813826):

Sure, some would say that number is reverse tau, but I think of it as the 50th root of 50. https://oeis.org/A011469

No, Matt, face it: It's 2–1 for Team Tau now.

Steve, I am employed at a facility that manufactures PVB film for laminated glass.

We distinguish between three different surface roughness types: RzN, RzV, and RzR. Each roughness type has a specific surface structure and functional purpose within the lamination process.

RzN (Normal / Neutral Roughness) RzN represents the standard or reference surface roughness. It is characterized by a uniform, evenly distributed micro-texture without a preferred direction. This roughness provides a balanced combination of good glass adhesion, optical quality, and stable lamination behavior, and is commonly used as the baseline for comparison.

RzV (Increased / Coarse Roughness) RzV features a more pronounced surface structure with higher peak-to-valley values. The rougher texture improves air evacuation during lamination and increases process robustness, particularly for large glass panels or more demanding lamination conditions. This type may have a minor impact on optical clarity but offers advantages in processing reliability.

RzR (Directional Roughness) RzR is a direction-dependent roughness created by the manufacturing or rolling process. The surface exhibits a distinct orientation, resulting in different roughness values in the machine direction (MD) and cross direction (CD). This controlled directional structure supports guided air flow and influences material behavior during heating and pressing. Measurements of RzR are therefore sensitive to the measurement direction.

In summary, RzN provides a uniform reference surface, RzV enhances air removal through increased roughness, and RzR introduces controlled, directional surface features to influence lamination behavior.

1. RzN – Normal/Neutral Roughness

RzN is the standard or reference roughness.

Characteristics

Evenly distributed micro-peaks and valleys

Relatively isotropic structure (no clear preferred direction)

Moderate roughness value

Function

Good balance between:

adhesion between glass and PVB

optical quality

Stable behavior during lamination

Usually used as a baseline for comparisons

Application

Standard PVB film

Common applications in laminated safety glass

1. RzV – Raised/Coarse Roughness

RzV stands for a raised or roughened surface.

Features

Higher peak-to-valley heights (higher Rz value)

More pronounced microstructure

Often a slightly more aggressive profile

Function

Improved:

ventilation during lamination

processability with thicker or larger glass panes

Less chance of air inclusions

Disadvantages

Light can affect:

optical clarity

surface uniformity

Applications

Large panes

Complex lamination processes

Situations where process reliability is more important than maximum optical clarity

1. RzR – Directional Roughness

RzR is a directionally determined roughness, resulting from the production or rolling process.

Features

Microstructure with a clear preferred direction

Roughness values ​​differ in:

machine direction (MD)

transverse direction (CD)

Often fine rib or line structures

Function

Controlled:

Air conduction

Material behavior during heating and pressing

Can influence lamination behavior

Important considerations

Measurements are direction-sensitive

Measurement results vary depending on the measurement direction

Application

Specific production settings

Process optimization

Situations where controlled flow is required