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Title
89
AskScience Panel of Scientists XVIII
270
AskScience AMA Series: "I am Rhett Allain, physicist and technical consultant on Mythbusters and MacGyver. Ask me about the physics of pretty much anything!
22505
Why is it that during winter it's not uncommon to have days with abnormally high temperature and summer-like weather, but in the summer it never drops to winter-like weather for a day?
172
If 2 people dislike the same food, are they then more likely to dislike other similar foods?
54
Does the Mach Cone occurs only appears when crossing the 1 Mach speed or it can also appear later during the supersonic flight (> 1 Mach)?
23
What was going on in the science community when the first dinosaur bones were discovered? Did we realize early on what we were looking at? What was the attitude of the community towards the discovery?
536
Can dogs observe and recognize aging in adult humans? Do they differentiate between young adult, middle-aged and elderly humans?
15
Could a planet with a highly eccentric orbit be tidally locked?
5
At what frequency does a repetitive sound become a solid sound?
23
Why don't the palms of our hands and the soles of our feet tan or burn?
6
Why are there so few species of mammals?
11
Is it possible to trigger or "activate" a volcanic eruption?
5
Are there any known mutations in drosophila melanogaster that cause a phenotype of folded downward wings?
11003
When does a mushroom die? When it's picked? When it's packaged? Refrigerated? Sliced? Digested?
5
Does the gravitational force of the sun and moon affect the atmosphere the same way it affects the tide? Is there an increase in oxygen during high tide/low tide?
6
Are blood bags usually sealed (in a vacuum)?
5
Is white light dispersed by a prism always the same? (angles to colour)?
9
When you physically break or shatter a flash storage chip, to what degree is the data still readable from the fragments?
3
Does energy accumulate in geographical faults in such a manner that the longer that energy isn't released, the bigger energy-releases we can expect at once? (i.e. earthquakes, volcanos).
37
Is it possible to transform martian soil into fertile soil through bacteria and fungi?
21
Do cats purr voluntarily or unvoluntarily?
1
When receiving donated blood, how do u screen for blood diseases before releasing them to hospitals?
5
How do processors make sure their calculations are done correctly when out of the billions of transistors they have, a few will surely fail over time?
4
Are seatbelt/phone detection cameras a real thing? And if so, how do they work?
14
What is the most amount of electrons forcibly added to an atom?
10
Why does the taste of tap water vary between locations?
6
Is there Ice at the bottom of Challenger Deep?
5
Can the Maillard reaction be reversed? Or, Is it possible to untoast bread?
50
Why do things like saliva or melted cheese pull into strings when you try to separate them?
0
How was the square mileage (or kilometers for the metric folk) calculated before satellites?
31
I think I understand the difference between aleph-null and aleph-one as countable and uncountable infinities, but what is aleph-two?
8
Do any of the stars we can observe with tbe naked eye at night have planets orbiting them?
8
How do developers of Nuclear Weapons either keep (or protect themselves from) radioactive materials like Plutonium-239 from potentially ‘leaking’ out particles? Are there any methods to contain these particles from escaping the material so they won’t hurt biological matter near the material?
10
If the vaporization point of water can be changed by increasing pressure, is the freezing point also affected by pressure?
2
Alternates to Xenon for Electric Propulsion?
9
How do we know what an asteroid is made of?
5
If wind is primarily generated by the rotation of the Earth, then how are some days windier than others?
8
The failed recovery of the Falcon Heavy's central core was attributed to the booster running out of TEA-TEB. How does this happen if the amount of fluid needed to ignite the engine, and the number of ignitions required is known beforehand?
4
What do we know about the effects of nanoparticles on the human body?
4
How did scientists determine where the Milky Way Galaxy begins and ends?
5740
Does a Mayfly, which only lives a day, evolve fast than a human?
10
How does a "loop sensor" in a street work?
195 RobusEtCeleritas In a beta-plus decay, it's not a single neutron which is decaying into a proton, it's an *entire nucleus* decaying into a new species. While a free proton can't decay into a neutron, beta particle, and neutrino due to energy conservation, an entire nucleus can decay to a species of lower mass by converting one of its protons into a neutron.
78 somedave An isolated proton is less massive than an isolated neutron yes, but a bound state of a neutron and proton is less massive than two isolated protons. This is due to the binding energy of the proton and neutron. Remember E = mc^2, so as the two isolated protons had more mass, they had more potential energy that the deuterium nucleus, this energy is released in a positron and neutrino that are emitted after fusion. Edit: Typo
20 [deleted] [removed]
7 centurion236 Classical physics gives us conservation of mass and energy, but these are approximations. Einstein proposed a system in which mass and energy are interchangeable, and mass-energy is conserved. You'll notice that every element is slightly lighter than the sum of its neutrons and protons. That "mass defect"is related to the forces and energy that holds the nucleus together. To enable positron decay, the decay must release enough energy to make up for the mass that is "spontaneously" created.
3 DrFeathers The whole system must have more energy than the state it wants to decay to. In the case of a free neutron you only have the neutron's mass to work with. Once you are in a nucleus, then you are considering the mass of all of the protons and neutrons as well as the binding energy. A proton can sort of "borrow" energy to allow a decay to happen, as long as the mass of the resulting nucleus will be lower.
195 0 RobusEtCeleritas In a beta-plus decay, it's not a single neutron which is decaying into a proton, it's an *entire nucleus* decaying into a new species. While a free proton can't decay into a neutron, beta particle, and neutrino due to energy conservation, an entire nucleus can decay to a species of lower mass by converting one of its protons into a neutron.
77 0 somedave An isolated proton is less massive than an isolated neutron yes, but a bound state of a neutron and proton is less massive than two isolated protons. This is due to the binding energy of the proton and neutron. Remember E = mc^2, so as the two isolated protons had more mass, they had more potential energy that the deuterium nucleus, this energy is released in a positron and neutrino that are emitted after fusion. Edit: Typo
19 0 [deleted] [removed]
5 0 centurion236 Classical physics gives us conservation of mass and energy, but these are approximations. Einstein proposed a system in which mass and energy are interchangeable, and mass-energy is conserved. You'll notice that every element is slightly lighter than the sum of its neutrons and protons. That "mass defect"is related to the forces and energy that holds the nucleus together. To enable positron decay, the decay must release enough energy to make up for the mass that is "spontaneously" created.
3 0 DrFeathers The whole system must have more energy than the state it wants to decay to. In the case of a free neutron you only have the neutron's mass to work with. Once you are in a nucleus, then you are considering the mass of all of the protons and neutrons as well as the binding energy. A proton can sort of "borrow" energy to allow a decay to happen, as long as the mass of the resulting nucleus will be lower.