#summerofphysics — Public Fediverse posts

This Altalena Gigante has a rope length L of 3.2m, which increases the duration T of one swing to 3.6 seconds, as T = 2 π √(L/g), with g = 9.81 m/s² (yes, irrespective of mass and amplitude, for small swings! This property was very important for timekeeping, using pendulum clocks). #SummerOfPhysics Acceleration (versnelling) measured with #phyphox app from @phyphox

The warmer an object, the more (infrared) radiation being emitted. This is detected by a thermal camera (typ. in the range from 3 to 14µm). Germanium is transparent for this IR (but not in the visible!), making it one of the materials used for #thermal camera #optics. #SummerOfPhysics 20/n

"Water boils at 100°C". Looks like a fundamental 'constant', but it is only true for a specific (atmospheric) pressure. Video of water boiling at about 60°C, using a syringe and some force to lower the pressure. Easier than taking the class to Mt Everest. #SummerOfPhysics #Physics #ITeachPhysics 19/n

Water isn’t colourless.
It absorbs longer wavelengths (red light) stronger than shorter ones (blue). If white #light can travel a long distance (deep pool, or in compressed #glacier #ice without scattering air bubbles), mostly blue light will remain. #SummerOfPhysics 18/n

@Hashtags @freyablekman 
One more #physicist here! 👋 Now running a thread #SummerOfPhysics on everyday #physics observations and experiments. In case you’re interested ;)

White objects are actually made of optically transparent, non-absorbing material. They appear white because light is scattered (= changed direction) multiple times due to roughness at the microscopic level. Think of snow ❄️, versus water or air-free ice. #SummerOfPhysics 17/n

Periodic reminder there’s gravity in space (see map below).
The #ISS #SpaceStation experiences a gravitational pull by the Earth of ~88% compared to the one at sea level. Thanks to its speed (~28000 km/h), this leads to a constant, almost circular fall around 🌍. #SummerOfPhysics #physics 16/n

The typical drawing of an #iceberg (first image) is physically not possible. It will rotate to a stable position (second image), making it more difficult to pass them safely (#Titanic!). Try it yourself with your own shapes: https://joshdata.me/iceberger.html. #SummerOfPhysics 15/n

The same thin film interference effect is used for lens #coatings (and glasses) to minimise reflection, and to max transmission. As this process depends on the wavelength, it doesn’t work equally well for all colours, leading to slightly coloured glasses. #SummerOfPhysics 14/n

The colors of #soap bubbles are caused by the thickness of the soap film (~0.0001mm) and the viewing angle. Light, being an electromagnetic #wave, reflects at top AND bottom of the soap film. #interference of both paths enhances/suppresses certain colours. #SummerOfPhysics 13/n

It takes a minute for the (#colour sensitive) cones in your #eyes to adapt to the dark - and +10’ for the rods - so, keep one eye closed if you have to go to the bathroom at night. When you switch off the 💡again, that eye has maintained its dark adaptation. #SummerOfPhysics #Optics 12/n

The #Moon close to the horizon only appears bigger, but isn’t. Test this by stretching your arm and looking at your little finger’s top. This gives an angular size of about 1°. The size of the 🌒 (and ☀️) is about 0.5°, so you can always cover it (see ALT text for photo). #SummerOfPhysics 11/n

At cruising altitude, air pressure is only 0.25 bar, while ✈️ cabin pressure is kept around 0.7 to 0.8 bar. The pressure difference is used to flush toilets. This leads to a small, yet detectable (with @phyphoxorg’s app) pressure drop in the cabin (➡️ALT). #SummerOfPhysics 10/n

The main reason why candles and torches have a (relatively cold) flame and #soot emission is… #gravity! This makes the less dense hot air rise fast, leading to an upward flame and incomplete burning. In the #ISS, a sphere-like, blue flame is formed.
#SummerOfPhysics 9/n

A rainbow is caused by water droplets, similar to a prism splitting white light in colors (☀️↦🔼↦🌈). Just before sunset, the sun is reddish, as blue-green has already been scattered in the sky. Hence, 💧can only 'reflect' (and disperse) orange-red light. #SummerOfPhysics 8/n

With every heartbeat, your chest moves up and down. So, according to Isaac Newton, there must be acceleration. The accelerometers in your phone are sensitive enough to pick up this signal. (Read out via @phyphox app; lying down with📱on my chest). #SummerOfPhysics #ITeachPhysics #PhysikEdu 7/n

Een #hagel steen van 4cm heeft een kinetische energie die ± 300x groter is dan een van 1cm, wegens E = ½mv².
Massa m is 64x groter (=4³), omdat het volume schaalt met (diameter)³.
Eindsnelheid v is ook groter, ± 100km/h ipv 40 km/h (door effect luchtweerstand; hangt af van precieze vorm). #onweer #CodeOranje #SummerOfPhysics

This water filled lavatory sink acts as a giant magnifying glass. Without water, the curved bottom of the glass sink hardly distorts the image, like a plane window. #optics #bananaforscale #SummerOfPhysics 6/n

One of my favourite demonstrations of #Archimedes’ principle. Put a dropper in a closed bottle. By squeezing the bottle, pressure increases, compressing the air inside. The water level increases in the dropper and the dropper sinks as the buoyancy decreases. #Physics #ITeachPhysics #SummerOfPhysics 5/n

An ⚡️charged PVC tube can bend a water flow. The H₂O molecules orient themselves (➕side is attracted by the ➖charges on the tube). The Coulomb force is distance dependent, so the attractive force is a tiny bit larger than the repulsion from the 💧's➖. #SummerofPhysics 4/n

A final pool experiment, with the
@phyphox app (➡️ALT). Every meter below the surface, pressure increases by ~ 100 hPa (or 0.1bar). Consequently, the pressure at the Titanic - at a depth of 4 km - is about 400 bar and the air column at sea level is equivalent to 10 meter of water. #SummerOfPhysics #physics 3/n

While you can look at any angle into a pool, the opposite is not true. Looking up from the bottom of a pool, you'll see - from a certain angle - the reflection of the floor instead of the air, due to total internal reflection at the water-air interface.
#SummerOfPhysics #Optics #Physics 2/n

Although this pond has everywhere the same depth, it appears a lot deeper on the near side. Light rays are bent when they cross the water-air interface (Snell’s law), distorting the image. The more perpendicular you look (near side), the less it’s distorted. #SummerOfPhysics (A daily toot on physics in everyday life. That's the plan.) 1/n