# Ceiling fan and impact force on the blades

• I

## Main Question or Discussion Point

A ceiling fan has kinetic Momentum in 1 blade hitting a fixed target. Would the design allow the other blades to flex , reducing target impact? If the 4 blades are combined and bolted together at same velocity is different Momentum delivered?
Similar q : a human arm is about 8kg and a sword about 1 kg. Does the hand-grip cause less impact than if the sword is welded into a steel-pin locked onto arm-bones?
( I'm guessing the answer is 50% maybe and it's not Physics..) ( but photos of skull damage and Newton calcs. suggest "yes" ).

Related Classical Physics News on Phys.org
russ_watters
Mentor
the design
What design?

The design of 4 flexible blades and a flexible central ceiling-rod .

jbriggs444
Homework Helper
2019 Award
The design of 4 flexible blades and a flexible central ceiling-rod .

At the moment in time of impact of 1 blade , will the other 3 blades have time to flex or will the total Momentum act on the 1 blade hitting target? This assumes the power is switched off shortly before impact so there is no added energy .

jbriggs444
Homework Helper
2019 Award
At the moment in time of impact of 1 blade , will the other 3 blades have time to flex or will the total Momentum act on the 1 blade hitting target? This assumes the power is switched off shortly before impact so there is no added energy .
See #2.

I gather Russ does not know the shape of ceiling fan and JB and I do not know something .
I believe if the target is un-fixed then the impact on it will be the same as if it's fixed. But a moving object with Momentum may have different principles ..

Last edited:
russ_watters
Mentor
I gather Russ does not know the shape of ceiling fan....
I know of several.

" When the ball strikes the bat, it causes the bat to bend slightly at the impact point. That bend then propagates along the bat up to the handle, reflects off the end of the handle and then travels back down to the impact point. The bend takes about 0.002 seconds to travel up to the handle and back again. But the ball is on the bat for only 0.001 seconds, and it bounces off before the reflection gets back to the impact point."
It's the missing .001 seconds that worries me .

berkeman
Mentor
@be unique -- are you trolling us, or do you just have really bad language translation software and do not know how to post links to what you are asking about? Try CTRL-C and CTRL-V.

What links? The answer would be 1) don't know , which is OK by me ,2) total Momentum of all blades is impacted by 1 blade on target or 3) an unknown deformation in the whole fan assembly absorbs a portion of Momentum at impact .

russ_watters
Mentor
Ok, well, that's enough. If you are serious about your questions you can PM me with something more coherent and detailed and I will consider adding it to the thread and re-opening it. Otherwise, thread closed.