The video opens with a cacophony of bangs and bonks, as the unseen officer loses a great battle. Suddenly, he toboggans into frame, turtle-style — legs first, face-down — whipping along the outer rim of the slide before he spills from its wide metal maw onto the ground.
After the clip of a Boston police officer catapulting out of a children’s slide at the recently renovated City Hall Plaza playground went viral, many wondered how the officer reached such an alarming speed. (The officer sustained and recovered from a minor head injury.) Boston Mayor Michelle Wu promised “to make sure there’s more signage that this is for children or something.”
Out of a shared concern for playground safety, HuffPost asked a physicist why the officer was going so fast and how others could avoid his misadventures.
“Normal people, when they go down a slide, they’re fine,” said Rhett Allain, an associate professor of physics at Southeastern Louisiana University and the author of “The Physics of Going Fast—but Not Too Fast—on a Giant Slide,” for Wired. “I would guess it has to be something about the clothes he’s wearing.”
All other things being equal, a child and an adult ought to go down a slide at the same speed. Yes, the earth’s gravitational pull increases with an object’s mass — but objects with more mass also accelerate more slowly, and the two factors perfectly cancel each other out, Allain said. It’s the reason why, if you drop a golf ball and a bowling ball from the same height, they’ll hit the ground at the same time.
“Normal people, when they go down a slide, they’re fine.”
The major difference-maker is friction.
“Friction depends on the two surfaces interacting, so if you have a metal slide and it’s in contact with skin or cotton clothes you have a certain coefficient of friction,” Allain said. “And if you change the material, maybe to something stiff, it could make it a lot slipperier.”
If the officer gave himself a little push at the top of the slide, he added, it could contribute but not altogether explain his velocity.
The video shows the officer dressed in a neon vest and a typical officer’s uniform. A slight sheen on the pants suggests the fabric is synthetic or tightly woven and slippery.
A public information officer for the Boston Police Department did not immediately respond to HuffPost’s request for comment on the material used to make officers’ uniforms.