I have a life science degree and even worked in research for a few years. So I feel I should be able to answer this question for myself, but yesterday my daughter blindsided me by asking why, if sound and light are both waves, light can travel through the vacuum of space but sounds can't?

So, I told her that one was a mechanical wave and other was an electromagnetic wave and ... then realised that was the extent of my knowledge. I was parroting stuff I'd learn years ago without any real understanding.

Can someone explain to me, ideally with science but without maths:

• what the difference is?
• why one requires a medium for propagation and the other doesn't?
• how come electromagnetic waves can still propagate via a medium (i.e. heat waves still carry heat energy through air, or the body)?
• whether all electromagnetic waves are quantized (i.e. light waves are made of photons but ... heat waves are too, right?)
• whether it's possible for a wave of each type to exist at the same wavelength?

EDIT: stepping back, it appears I have caused confusion born of ignorance. Essentially, while I can understand the properties of a mechanical wave simply by observing it, I am struggling to understand how intangible things like heat and light can have the same properties.