Originally posted by h1a8Guess how much pressure a hypodermic needle applies with just 1 pound of force? Hundreds of tons per square inch of pressure.
Wrong.
"A 1-pound force applied to a hypodermic needle's tip results in a pressure of about 17,600 pounds per square inch (psi)."
That's 8.8 tons, not hundreds. /maths
Originally posted by Robtard
Wrong."A 1-pound force applied to a hypodermic needle's tip results in a pressure of about 17,600 pounds per square inch (psi)."
That's 8.8 tons, not hundreds. /maths
The cross-section of the needle's very tip is approximately a rectangle or a very acute ellipse. For simplicity, let's assume it's a rectangle.
(Note: using an ellipse would give a slightly smaller area and thus a slightly larger result.)
Effective contact dimensions at the tip:
0.02 mm by 0.05 mm, which is 0.00002 m by 0.00005 m.
Area (A):
0.00002 m × 0.00005 m = 0.000000001 m² = 1.55 × 10⁻⁶ in²
Calculate pressure at the tip:
P = 1 lbf ÷ 1.55 × 10⁻⁶ in² = 645,000 psi, or approximately 323 tons per square inch.
As the needle penetrates deeper, the contact area increases, but the pressure still remains in the range of multiple tons per square inch.
Here's a link showing the tip under a microscope. I disagree with the author's assumption that the cross-section is approximately the size of a circle.
https://groupivprojectgroup6.wordpress.com/force-of-the-hypodermic-needle-tala-mansouri/