Recent comments in /f/askscience

DucksVersusWombats t1_j4v2ooo wrote

Reply to What happens to the energy of sound in space? by full_hammer

But space is filled with gasses of varying degrees of rarefaction. How dense does gas have to be to propagate sound waves?

Space is filled with periodic and aperiodic events; can't some of them be interpreted as sound?

What frequency or amplitude of vibration in a gaseous medium do we decide isn't sound?

1

SethSky t1_j4v2lgd wrote

Reply to What exactly happens in your body when you touch or consume a radioactive substance i.e U235 or Pu239. What happens on the cellular level and how the brain & nervous system deals with it? by Baby-saint

When a radioactive substance is touched or consumed, the radioactive particles release energy in the form of ionizing radiation. This radiation can damage or kill cells in the body, leading to various health effects depending on the amount and duration of exposure.

At the cellular level, ionizing radiation can damage DNA and other cellular structures, leading to mutations and cell death. This can increase the risk of cancer and other diseases. The brain and nervous system can also be affected by ionizing radiation, leading to cognitive impairment and other neurological effects.

Our body does not naturally build a defense mechanism against ionizing radiation.

7

SethSky t1_j4v1sw4 wrote

Reply to What determines the lifespan of a species? Why do humans have such a long lifespan compared to say a housecat? by Forking_Shorts92

The lifespan of a species is determined by a combination of genetic and environmental factors. Genetic factors include the presence or absence of certain genes that are associated with aging and disease, while environmental factors include access to food and water, exposure to toxins and pollutants, and susceptibility to predators and disease.

Humans have a relatively long lifespan compared to many other species, including housecats, due in part to genetic factors such as the presence of telomerase, an enzyme that helps to maintain the integrity of chromosomes and therefore the longevity of cells. Additionally, humans have a relatively low rate of predation and access to medical care and other forms of protection from disease, which also contribute to our longer lifespan.

Early human life expectancy was ably about only 20 years too.

3

MoodiusJ t1_j4uy70q wrote

Reply to What happens to the energy of sound in space? by full_hammer

The energy is contained in the wave motion of matter. To set up this problem you need some Region of matter ie fluid or solid then a boundary with vacuum. This boundary will have conditions imposed on the pressure, fluid velocity or lattice displacement wave equation of the sound. With a solid-vacuum boundary it will cause a full reflection of the wave at the boundary and the energy will remain constrained in the matter region and eventually be dissipated in the solid.

With a fluid vacuum boundary things are a bit more interesting because typically that boundary will not be sharp because of diffusion. For exampke,, in the upper atmosphere of earth you will get a gradient of air density with altitude. The sound's wavelength and speed will be a function of density and temperature and therefore altitude as will its impedance per unit length so if you launch a wave up from the surface it will both spread out transversely and some of the power will be reflecting back toward the surface as it moves per unit length.

2

MrNobleGas t1_j4uwokd wrote

Reply to comment by JonJackjon in How does lightning illuminate the sky? by AverageMan282

You're thinking of black-body radiation, the phenomenon where an object emits electromagnetic radiation purely because it has a temperature greater than zero.

There are electric charges inside the object - nuclei and electrons. This creates electric fields. When an object has temperature, its particles move around, which means they undergo acceleration. A charge undergoing acceleration in an electric field scatters that field (which also happens when that field is what caused it to move), which creates propagations in that field - electromagnetic waves - light. The higher the temperature, the higher the energy, and Planck gives us a direct relation between energy and frequency. Higher frequency means shorter wavelength. Sufficiently hot objects will therefore emit visible wavelength, while something as warm as, say, a human body emits lower-energy infrared radiation.

2