Europe
News and information from Europe ๐ช๐บ
(Current banner: La Mancha, Spain. Feel free to post submissions for banner images.)
Rules (2024-08-30)
- This is an English-language community. Comments should be in English. Posts can link to non-English news sources when providing a full-text translation in the post description. Automated translations are fine, as long as they don't overly distort the content.
- No links to misinformation or commercial advertising. When you post outdated/historic articles, add the year of publication to the post title. Infographics must include a source and a year of creation; if possible, also provide a link to the source.
- Be kind to each other, and argue in good faith. Don't post direct insults nor disrespectful and condescending comments. Don't troll nor incite hatred. Don't look for novel argumentation strategies at Wikipedia's List of fallacies.
- No bigotry, sexism, racism, antisemitism, islamophobia, dehumanization of minorities, or glorification of National Socialism. We follow German law; don't question the statehood of Israel.
- Be the signal, not the noise: Strive to post insightful comments. Add "/s" when you're being sarcastic (and don't use it to break rule no. 3).
- If you link to paywalled information, please provide also a link to a freely available archived version. Alternatively, try to find a different source.
- Light-hearted content, memes, and posts about your European everyday belong in other communities.
- Don't evade bans. If we notice ban evasion, that will result in a permanent ban for all the accounts we can associate with you.
- No posts linking to speculative reporting about ongoing events with unclear backgrounds. Please wait at least 12 hours. (E.g., do not post breathless reporting on an ongoing terror attack.)
- Always provide context with posts: Don't post uncontextualized images or videos, and don't start discussions without giving some context first.
(This list may get expanded as necessary.)
Posts that link to the following sources will be removed
- on any topic: Al Mayadeen, brusselssignal:eu, citjourno:com, europesays:com, Breitbart, Daily Caller, Fox, GB News, geo-trends:eu, news-pravda:com, OAN, RT, sociable:co, any AI slop sites (when in doubt please look for a credible imprint/about page), change:org (for privacy reasons)
- on Middle-East topics: Al Jazeera
- on Hungary: Euronews
Unless they're the only sources, please also avoid The Sun, Daily Mail, any "thinktank" type organization, and non-Lemmy social media. Don't link to Twitter directly, instead use xcancel.com. For Reddit, use old:reddit:com
(Lists may get expanded as necessary.)
Ban lengths, etc.
We will use some leeway to decide whether to remove a comment.
If need be, there are also bans: 3 days for lighter offenses, 7 or 14 days for bigger offenses, and permanent bans for people who don't show any willingness to participate productively. If we think the ban reason is obvious, we may not specifically write to you.
If you want to protest a removal or ban, feel free to write privately to the primary mod account @EuroMod@feddit.org
view the rest of the comments
No, that's not the case. What's relevant, especially with a difference of mass so large, is the relative speed of the two objects, which is 30 km/h.
@Alerian@sh.itjust.works
Suppose the impact coefficient k is similar, it does make a difference whether a bike crashes into a standing car (case 1) or a car crashes into a standing biker (case 2).
collapsed inline media
The thing is: You are using velocities v1, v2 which are relative to Earth. But none of the two vehicles collide with Earth - they collide with each other, thus the thing that matters is their relative speed, thus the difference of their velocities relative to Earth.
(That's also why the speed at which both Earth, the car, and the motorized bike move around the sun does not matter - relative speed is all what matters).
The other thing is that a human colliding with an object of several tons weight with a speed of, say, 36 km/h is not "elastic". 36 km/h is 10 meter per second, which is equal to about one second of free fall (accelerating with a= 9.81 meter per square second to the ground), which is equivalent to a fall height of h = a/2 * s ^2 or 5 meters.
Somebody falling from 5 meters hight on hard concrete ground will not bounce up but will likely have some broken bones, or a broken skull. What happens is that all parts of thier body is decelerated to a speed of zero within a distance of one or two centimeters, which involves massive forces that easily break bones.
And a speed of 14 m/s, or 54 km/h corresponds to a fall of ten meters depth - almost certainly lethal if hitting a two-ton concrete block.
The formula includes the relative speed (v_2 - v_1) of both bodies. Derivation, see Wikipedia or a book on engineering mechanics.
case 1, k=0. Fortunately, a car is not solid rock. I don't know about a typical of k for collissions of humans with a car, but if you say it's 0, that's actually good for the biker, as the forces then acting on their tissues is smaller than if that would not the case.
So concluding. If the collision of the biker and the car is completely inelastic, it doesn't matter if the biker crashes into a resting car or the car crashes into a standing biker. The only thing that matters is the relative velocity of the two objects.