Physics Friday: The Flash Breaks The Sound Barrier on TV

Every Friday, we take an opportunity to explore the science at work in some of our favorite comics. Since last week’s Physics Friday was all about how fast The Flash runs in the comics, it seems only natural that this week we look at an exclusive Comic Con promo for this fall’s The Flash on The CW, in which we get a different look at how fast the Scarlet Speedster can go.

In the promo, Barry Allen goes speeding by the police car at 760 miles per hour, only just shy of the speed of sound! Just after that, we here a sonic boom off in the distance which indicates that Barry has probably accelerated up past the 762 miles per hour necessary to break the sound barrier. So the question we will be seeking to answer is: How fast does The Flash accelerate between when he passes the police car and when he breaks the sound barrier?

The first thing we need to do is convert our numbers into units we can use. In real life, we measure speed in miles per hour. In physics though, we measure it in meters per second. So we need to know how fast Barry is going in meters per second. Converting the 760 mph he runs past the police car at to m/s would give us 339.75 m/s. Then we know he accelerates up past the sound barrier, which is 340.29 m/s. These numbers will be our initial and our final velocities.

The other piece of information we need to collect from the video is how much time passes between when the police officers’s radar gun picks up Barry, and when Barry breaks the sound barrier. This might be a little tricky, since the video goes into slow motion for a minute, but we’ll give our best shot. Judging only by the sound of the boom and the time given by the slider in the video, it seems that it takes Barry about 2 seconds to accelerate up to his final velocity.

We can use these three numbers to solve for his acceleration. To do this calculation we will use the equation

We already know three of these four variables, so solving it should be a breeze. Plugging in what we know, we find

With an acceleration of only about 0.3 meters per second per second, Barry is surly just cruising along enjoying his newfound super powers, rather than rushing to an emergency. And either way, he looks amazingly cool doing it.

What do you think? Does Barry’s acceleration in this clip measure up to the expectations set by the comic book last week? Do you think the new Flash show looks awesome? Were you pumped when you saw the police officer write in “Grodd” on his crossword? Sound of below and be sure to check in next week when we explore the physics of a different comic book title.

As always, thanks for reading.