A question for the physics folks

[Pulp]

How far would a person have to fall to have an impact speed of 8mph?

I do the 5 minutes safety talk at work every shift. Our lift trucks are governed to 8mph, so I was doing examples of how fast 8mph really is, like most folks can easily run 8mph, so run face first into a tree and you'll see how fast 8mph really is. Then I said 8mph is the speed you'd be going if you fell from 15 feet, but I'm not sure that is correct. I just don't have the math skills to put all them letters and symbols on a chalk board and come up with the real distance you'd have to fall to have an impact speed of 8mph.

 

[excat]

32.2 fps is free fall velocity of our gravity - to sum it up, depends on how long the fall takes, longer it takes, the faster the speed, and i can't say i've ever timed a fall.

if it took 2 seconds to fall - 43.9mps
1 second - 21.9 mps
.5 sec - 10.97
.25 (1/4) sec- 5.48mph

I would think you would be pretty darn close on your guesstimation, somewhere between .25-.5 sec to fall.

I think my math is correct there - I'm sure someone will correct me if I'm wrong. Numbers are all rounded.

 

[AKguy1985]

I'm no math whiz, but i'd go with whatever you say lol.

 

[doctorjj]

Your free fall speed at impact from right at 2 feet would be 8 mph. A 15 ft fall, you would impact at 22 mph.

 

[rhodesbe]

Since Force = Mass * Acceleration, the magnitudes between a forklift and a human impacting at 8mph are vastly different:

Forklift: ~43hp = 23500 lb/ft/s = 2000 pounds * 11.75 feet/s (8mph)
Human: ~4hp = 2056 lb/ft/s = 175 pounds * 11.75 feet/s

You're talking about 1/10th of the force between a dude running into a wall, and a forklift running into anything.

[edit: and your forklift prolly weights more the 1 ton, too. The class 4 lifts that are rated for 5000 pounds weigh a minimum of 8500 pounds]

 

[Cohiba]

I use to help my nephew with some of his homework...but right now its just to dang early to think about Newton amd his laws and drag, friction and velocity.

Google...splat calculator...use it. Then you'll have a visual on your power point for your class.


7:45am ....wow...waaaay to much single barrel Jack Daniels and Schlitz last night. I gotta quit drinkin' during the week...getting to old amd losing to many brain cells.

 

[Lurker66]

Yipes this thread is causing me to have flashbacks to highschool math class.

Ive got an urge to goto bathroom n get a dip of skoal an read Louis L'lamore.

 

[TwoForFlinching]

32.2fps/ps is terminal velocity. It takes time to build that speed... But there are studies out there that suggest that first full second of fall is anywhere between twelve and eighteen feet, depending on relative height/air density. Without busting out the whiteboard this early, 8mph is just under 12fps constant. It would take between 12 and 14 feet to achieve an 8mph fall

 

[Traxxis]

http://www.greenharbor.com/fffolder/speedtime.pdf

 

[120 Acres]

Just hit someone with the lift and say "See, this is what will happen".