I have to write an assignment (1000-1500 words) with a topic from physics. I have been thinking for a month now, but still can’t find a suitable topic which I could expand to 1000 words. So, I was thinking, why not ask here.
Does anyone have any suggestions on what to write? I want something fun and appealing to general public but still a bit “professional”. And if it is about unicycling or juggling, even better. 
Roller coasters. You could design your own ride and analyse the motion in the turns and loop-to-loops (to make sure noone dies 
). You can make it as simple or as complicated as you want. I did this in my senior physics, t’was alot of fun 
if you’re doing calc based physics, and you’ve gotten through torques, angular momentum and rotational motion in general then you could analyze the various contact forces and torques between unicycle, rider and ground to display the details of what is dynamically taking place while someone rides a unicycle
What’s 1k words, about a page and a half? You can BS just about any topic you want in 1k to 1.5k words. Pick something, make an outline (that’ll help you brainstorm) and go for it. You’ll have 1k words before you know it. In fact, it should be hard for you to keep it under 1.5k words. That’s what I would worry about.
Try how the earth’s rotations cause different climate areas around the world - including why the equator is dry, and then the tropical regions around 30deg, then deserts, then temperate. You could write 10 pages on that after you research it, easy. Give lots of examples. Examples fill up pages. Oh, an don’t forget rotation driven ocean currents. You can give cool facts like how Rome and Minneapolis are at the same lattitude, but have hugely different climates because of ocean currents. (likewise England’s N lat put it right in the middle of canada - if it weren’t for their nice Atlantic currents they’d be freazin’ their buns off.)
Or try how electricity works, AC vs DC, how it’s transported and made, how a transformer works - that’s a 5 pager right there - 10 if you add in history.
Think of anything interesting, research it online and take notes, outline it, and poof, done paper.
write about black holes. theyre extremely interesting and you can easily write a long report on them.
string theory?
he’s only 17
write about the standard model, which is a theory that encompasses practically everything
good stuff
or you could write about the ol cliched double slit experiment
i don’t think its gonna be possible to have a unified theory. different laws govern the big and the small.
Just don’t let the universe know or it will fall apart.
Hmmm… But first take a three year course on group theory, field theory, quantum mechanics and relativity. 
The history of particle physics that led to the standard model is interesting and accessible. As are the things the model does not explain, such as the existence of mass.
Or go earlier: Rutherford scattering (Rutherford scattering - Wikipedia), Thompson and the electron, and other experiments leading a good understanding of atoms. These are simple experiments which had world-changing consequences.
If you want something topical, you could see what you can make out of a layman’s review of Loop Quantum Gravity, one promising alternative to String Theory. The exciting new Large Hadron Collider is surely worth a mention in this context.
The maths of general relativity is not even worth considering, but a qualitative explanation of its main ideas (surprisingly simple), predictions,
and experimental tests might be interesting.
Wave particle duality is always worth a go.
Al
That are awesome suggestions and I thank you for them, but to be honest, I need something simple. See, it’s for some english subject and we should write it mostly for practicing English. It just has to be a physics topic. So, I don’ want to bore everyone with equations and data. I need something fun.
Well, there is a lot of physics in unicycling, no? If not, I love gyroscopes. You must have tried this: http://www.exploratorium.edu/snacks/bicycle_wheel_gyro.html
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Al
Gyroscopes look fun. If I find enough material, I just might give them a try 
Write about how mass, length, and time are not fundamentally invariant between different coordinate systems.