You are here:

# Physics/Screw falling vertically

Question
QUESTION: F = m*a
a = 9.8 m/(sec^2), correct?
Why a screw falling vertically from a distance of 100 meters causes more damage than a screw falling vertically from a distance of 1 meter?
I am told that it is because of the formula F=m*a, but if I use a=9.8 m/(sec^2) then where is the distance?
Please explain. This is not homework.
Thank you.

ANSWER: Please, this is pretty obviously homework or a bar argument.  And you told me the distances, 100m and 1m.  If you just need to know if it causes more damage from falling from higher up then of course it does...it takes quite a few meters to reach terminal velocity.  If you need to know why there's no distance in the formula, then you need to either integrate the formula you were told to use over time or use the correct formula for velocity under constant acceleration.  v^2=vo^2+2ah, in this case.  Proper manipulation of F=ma will get you that formula, but why re-invent the wheel?

---------- FOLLOW-UP ----------

QUESTION: Dear Dr. Stephen O. Nelson,
Thanks a lot for your previous response.
Now I know that the formula to use in this case is v^2=vo^2+2ah, which has “distance” (h) in it.
Questions:
(1) a=9.8 m/(s^2), where “a” is Gravity acceleration, correct?
(2) How exactly can I see in the formula that the damage is bigger when “h” is higher? All I can see in the formula is that “v” is bigger when “h” is higher, but I cannot see there why the screw would cause more damage when falling from a higher distance. IE: Why the bigger “v” causes more damage?
Please explain; this is something I “want” to understand after have being told the story of the screw falling from certain height.
Thank you,
Leonardo

If it has a higher velocity on impact, then it has more momentum and energy to impart to whatever it hits.  That's why it causes more damage.  The thing is, small things like screws or coins don't actually get up to a very high velocity when you account for drag forces from atmospheric resistance.  Therefore they never really cause severe amounts of damage.

Physics

Volunteer

#### Dr. Stephen O. Nelson

##### Expertise

I can answer most basic physics questions, physics questions about science fiction and everyday observations of physics, etc. I'm also usually good for science fair advice (I'm the regional science fair director). I do not answer homework problems. I will occasionally point out where a homework solution went wrong, though. I'm usually good at explaining odd observations that seem counterintuitive, energy science, nuclear physics, nuclear astrophysics, and alternative theories of physics are my specialties.

##### Experience

I was a physics professor at the University of Texas of the Permian Basin, research in nuclear technology and nuclear astrophysics. My travelling science show saw over 20,000 students of all ages. I taught physics, nuclear chemistry, radiation safety, vacuum technology, and answer tons of questions as I tour schools encouraging students to consider careers in science. I moved on to a non-academic job with more research just recently.

Education/Credentials
Ph. D. from Duke University in physics, research in nuclear astrophysics reactions, gamma-ray astronomy technology, and advanced nuclear reactors.