Presenting to middle-schoolers on black holes - suggestions?

[Ghostcrown]

My professor wants me to make a 15 minute oral presentation on black holes for an event we have going on on campus. How should I structure it? I think I have a pretty good understanding of the concept of a black hole, but I don't want to get caught off guard during the 5 minute Q&A section. My other question is - what questions should I prepare myself for? Keep in mind that these are kids, not astrophysicists.

 

[UncertaintyAjay]

You should start with a basic sort of explanation of what a black hole is, how light cannot escape from it etc ( i'd say avoid talking much about event horizons and such). Then about how they form, so a short summary of the life cycle of a star, followed by a small bit about the Chandrasekhar limit . And include some cool pictures.
I'm in my last year of high school so all i know about black holes is what I've read in Stephen Hawking's The Theory of Everything. It was explained very nicely and with no mathematical arguments. So a condensed, slightly simplified version of that might be along the lines of what you're looking for.

 

[mgkii]

If you want to avoid difficult questions - and by that I don't mean questions you can't answer, I mean questions you are going to find difficult to explain in the language of middle-school in a 5 minute Q&A!... then I would suggest you steer clear of absolutes that just beg the questions "Why?".

So, for example; rather than stating that nothing can travel faster than light ("Why Sir?", "How do you know sir?") you can build up to the concept in a meaningful way without digging yourself a trap of questions - for example:

- The reason you feel heavy on Earth and not in space (**) is down to gravity, and the more massive an object is, the greater its gravitational pull will be.
(** Yes yes - we all know this is not quite true and means "far far outer space" rather than in orbit... but you don't need to explain that :-)
- We can see this in our own solar system - if you go stand on the moon you would feel lighter, and if you were able to stand on Jupiter you would feel heavier.
- We also know that gravity can even bend light! You need whole galaxies of mass to see it easily, but with really careful measurement we've even managed to observe it around our own sun. It was a tiny tiny bend, but it was there...
- So our sun can bend light a little. So let's imaging something that can bend light a lot...
- Let's imagine something that is so massive that not only can it bend light; any light trying to escape from it would get bent straight back at it. Well if no light can get away from it, then it would be black. That takes care of the first part of "Black Hole".
- So this Black "thing" is massive. So you'd think it would also be Huge yes? Well... no actually. Its gravity also works on itself, squisihing (technical term :-) it down into a something so small we can't can't even measure how small it is! That's where the hole comes in!
- And so on...​

Its rough, so please take it with best intentions

Regards
Matt

 

[ogg]

If you "have a pretty good understanding of the concept of a black hole." then consider a thought experiment where the Moon is suddenly replaced by a b.h. of the exact same mass and orbit. I find certain aspects of the other two posts (so far) problematic. IMHO, the most common question about bhs is "what happens when you fall in?" Are you able to handle that? You also have to decide on what perspectives you use. A couple of points: 1st: BHs are theoretical, not yet demonstrated. New physics is required for there to be any objects with finite density between BH & neutron (or quark) density, but that doesn't prove that what we are claiming are BH's are not something else. (There's articles about future satellites which will begin to observe near bh horizon). 2nd decide what a bh is (or to discuss that question). Is it everything inside event horizon or the singularity? Not discussing EH is lame. Note that EH is the end of both space and time. 3rd BHs might come in sizes (and evaporate). Almost all galaxies have one or more BHs in their centers. 4th: if the Moon were replaced with a BH (if you don't know this, then you're not ready to present to anybody) then we'd notice this because it disappeared, not because it would "suck" Earth into it. Tides wouldn't change. (I'm not sure what effect frame dragging will have...). 5th. Is it meaningful to SCIENTIFICALLY discuss what happens (what "is" ) inside the EH? 6th With a sufficiently large BH, tidal effects might be sufficiently weak for a probe to NOT be shredded at the EH, but so what? 7th The accretion disk (and jets) are the spectacular aspects of BHs. Most Middle Schoolers will have heard of BHs, why not Google "BH Myths", since the amount of material to cover for even a basic discussion is far more than 15 minutes worth - which is why I wrote that you have to decide on what you want to cover. I'd suggest looking at Yahoo! Answers to get a feel of the common questions. You'll tell by their sophistication whether they're written by kids or not. 8th since what happens inside BH depends heavily on the quantum physics of gravity (which we don't have a clue about), there are things we know about (or think we do) that don't (yet) fit into a neat scientific world view. Talk about what's interesting to you.

 

[sophiecentaur]

There are a number of misconceptions about BHs that would be worth dispelling. For a start, a BH doesn't 'suck everything inside itself'. Things need to be traveling fairly close to it, fairly slowly and towards it. The possibility of orbiting for ever round a BH is not considered by the 'public'. (The Moon question, above is along these lines, too.)