×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Units conversion for impact test - ft.lb to Joules

Units conversion for impact test - ft.lb to Joules

Units conversion for impact test - ft.lb to Joules

(OP)
I've got a US spec which asks for a 100ft.lb impact test done by a drop tube. I almost can't bare to ask this, but what is the height and weight for that test?

If it's really a 1 lb weight from 100 feet, or 100lb from 1 foot, that's (please check!) a 5kg weight from 2.8m or 137 Joules.

The reason I ask is a European spec asks for 20J impact which I'm confident we can meet, so I'm really hoping I've miscalculated this 100ft.lb

RE: Units conversion for impact test - ft.lb to Joules

1J=1N * 1m so 100 ft*lb = 13.825 kg*m = 13.825*9.81 N*m = 135.6 N*m = 135.6 J

RE: Units conversion for impact test - ft.lb to Joules

(OP)
Yes, that's the same as I got with a couple of my rounding errors.

I was really hoping to be wrong by a factor of 10, something to do with lb weight and lb force....

RE: Units conversion for impact test - ft.lb to Joules

ther are a bizillion unit convertors online.

another day in paradise, or is paradise one day closer ?

RE: Units conversion for impact test - ft.lb to Joules

Unit conversion doesn't seem to be the problem here. The problem seems to be order of magnitude. Why is the U.S. spec 135 J and the ISO spec 20 J? Is one of them a typo or is something really different?

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. —Galileo Galilei, Italian Physicist

RE: Units conversion for impact test - ft.lb to Joules

(OP)
I know there are a bizillion converters online, but I don't necessarily trust them.

zdas, I've got two different specs for a similar product, one says 100ft.lb and the other says 20J. By my (and RobyengIT's) calculations they are very, very different. I was looking for someone to say I had made a mistake and that 100ft.lb was around 20 Joules

RE: Units conversion for impact test - ft.lb to Joules

gareth71,

Your phrasing makes me nervous. You can generate 100ft.lb energy by lifting a 100lb weight 1ft, or by lifting a 1lb weight 100ft. When the weight arrives back at the ground, the 100ft.lb will be in the form of kinetic energy, less air resistance.

100ft.lb×4.45N/lb×.3048m/ft=136N.m, as noted above.

--
JHG

RE: Units conversion for impact test - ft.lb to Joules

(OP)
ok, thanks everyone. It looks like my answer was correct and we'll be non-compliant on that part of the spec. 136 Joules is an enormous impact energy to survive, especially as the other requirement is only 20J.

But thank you for your help!

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources