Let's just use the Firebolt as our model.
The Firebolt is said to reach 150 miles per hour in ten seconds. Let's just ignore air resistance for the moment and assume this is constant acceleration.
150 miles per hour = 67 metres per second
acceleration = change in velocity / change in time
a = Δv / Δt
a = (67 m/s)/(10 s)
acceleration = 6.7 m/s/s
That's pretty impressive. Almost exactly on par with a Ferrari Enzo going to 100 mph in 6.6 seconds!
Unfortunately, we have no way of knowing the mass of the broomstick pilot when they compiled that figure. So let's just ignore the varying masses of different potential riders and concentrate on the broom.
Anyway, here's the question: What is the Firebolt's top speed in an atmosphere?
I do not think the 150 mph figure is an indication of its top speed, rather it is a measure of its acceleration. Much like how in the Muggle world, in which the performance of cars is expressed in how many seconds it takes for the vehicle to reach 60 mph, wizards seem to express acceleration by switching the two factors - having time as the fixed number, and seeing how fast the broom will go in that period.
We have two canon examples:
Firebolt: 0 to 150 mph in 10 seconds
Cleansweep 11: 0 to 70 mph in 10 seconds
Given that the time factor is the constant, this leads me to believe that both of these broomsticks are capable of going faster than the respective 150 and 70 mph figures.
But how fast?
Without a rider, a broomstick by itself is a relatively aerodynamic object. Let's just say that this Firebolt can fly without a rider. What do you think would be its top speed at sea level? At jet-cruising altitude (around 10,668 metres for many airliners)?
And for that matter, what do you think would be the maximum cruising altitude of a riderless Firebolt? Considering that brooms do not need any kind of fuel or oxygen to operate (as far as we know), could a broom conceivably just fly off into space, if we ignore the human factor?
Now for a rider. A Harry Potter-shaped mass is not very aerodynamic, obviously. What do you imagine to be the top speed of a Firebolt with a rider? Given air resistance, could it even be lower than 150 mph, as stated in the advertisement? Of course, there are probably spells to reduce drag, so how much would this increase performance?
And here's another question. What do you think is the endurance of a Firebolt?
Brooms don't need fuel. Given this fact, we have several options:
- The broom can fly until it feels 'tired'
- The broom can fly until the charm that makes it fly wears off
- The broom can fly forever
What do you think would be the endurance, given options one or two?
And to get a bit science-fictional, let's contemplate what would happen if you stick a broom in the vacuum of space.
First of all, do you think a broom will be able to operate in space? Remember, it doesn't require fuel or air to burn, as it is propelled by magic. But could this magic still work in a vacuum?
And now for the big one:
If the broom can work in the vacuum of space, could it reach the speed of light? Beyond?
For all intents and purposes, the broom is a reactionless drive, meaning it doesn't need to throw stuff out the back in order to go forward. So, freed from fuel constraints, the broom could just keep accelerating until the spell on the broom wears off, which could be a very long time. Now, 6.7 m/s/s is rather slow acceleration when we're talking about interstellar distances, but the broom could feasibly accelerate at this rate for years, if the spells hold up. And if it can accelerate at 6.7 m/s/s constantly, and with no pesky fuel and reaction mass issues to worry about, I believe it is possible for this broom to get to 99.99% of light speed (since Einstein says you can't actually reach it) in less than two years (at 1 g, or 9.81 m/s/s, you can almost reach light speed in just about a year). What do you think?
But what about faster-than-light travel (FTL)? The laws of physics say that FTL travel is impossible, but as we well know, magic laughs in the face of science. Is it possible that this broom, being a reactionless drive (and possibly also having spells to reduce its mass to nil), could travel faster than light? Is magic the solution to the problems of FTL and interstellar travel?
Tim the Enchanter