What is the net force and kinetic energy of an 800g part hitting at 170mph?

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Discussion Overview

The discussion revolves around the net force and kinetic energy experienced by Formula 1 driver Felipe Massa when struck by an 800g coil suspension spring traveling at 170 mph. Participants explore the implications of the impact in terms of physics, particularly focusing on force calculations and kinetic energy, while considering the context of a high-speed racing environment.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions whether the net force can be calculated simply using the equation f = m x a, converting the mass from grams to pounds and speed from mph to feet per second.
  • Another participant argues that to determine the force, the contact time between the spring and Massa would need to be known, suggesting that kinetic energy might be a more relevant measure.
  • A further contribution likens the impact to a bullet, describing the nature of the collision as "instantaneous" and emphasizing the spring's motion prior to impact, which may have been influenced by its interaction with a tire.
  • One participant calculates the kinetic energy of the spring at the moment of impact, estimating it to be around 2.3 KJ, and compares it to the kinetic energy of a typical bullet, noting differences in potential tissue damage due to the helmet's distribution of force.

Areas of Agreement / Disagreement

Participants express differing views on how to approach the calculation of force and the relevance of contact time, indicating that there is no consensus on the best method to analyze the impact. The discussion remains unresolved regarding the exact calculations and implications of the impact.

Contextual Notes

Participants highlight limitations in their calculations due to assumptions about contact time and the nature of the impact, as well as the complexity of translating high-speed collisions into simple physics equations.

Neo-Newtonian
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This past weekend - Sunday, July 26th to be precise - Ferrari Formula 1 driver Felipe Massa suffered a HORRIBLE head / eye injury in the Grand Prix of Hungary as a result of an object striking his helmet and visor after having been "thrown" (disconnected) from another racing car ahead - an 800 g coil suspension spring. He was traveling (according to telemetry) approximately 170 mph at the moment of impact.

What was the net force of impact upon him - in "American" units?

Is it a simple f = m x a equation? If so, 800 g = 1.764 pounds of "mass" and his speed (acceleration or velocity) - 170 mph - equals almost 250 feet / second. Where do I drop out the "second" and call this about 440 pounds / feet of energy striking him?

Or is there a more correct formula?

(Trying to convince those in a non-technical office environment as to the laws of physics acting upon us ...)

Thank you.
 
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Not quite, to know the force you would have to know how long the spring was in contact with the driver.
Assuming the spring was stationary when he hit it, it will be accelerated upto the speed of his car (170mph) the quicker this happens the more force involved. It's very difficult to calculate this - you are probably better thinking in terms of the kinetic energy.
 
As far as "contact time", this could best be described as a bullet - a rather s-l-o-w, *reverse motion* bullet - that is, the object did not penetrate the human form in the same manner. It (the impact moment) could be called "instantaneous" as in "a glancing blow".

By "reverse motion", I'm being cute: Massa and car were in projectile(s) motion; the semi-stationary object (the 800 g spring) the target. In fact, suspend a bullet in mid-air for a split-second and force a target into it; that's a more proper scenario.

Television replays appeared to show the spring in motion (?) TOWARDS the driver that was hit - or perhaps almost suspended in air as if rebounding (from a bounce on the tarmac racing surface) due to being thrown (or projected) after the part became disconnected. The illusion of being propelled backwards cannot be discounted as it was possibly given momentum from coming in contact with a (rapidly rotating) rear tire of the vehicle that lost it.

The spring WAS freely airborne when it came into contact with Massa's visor and the impact clearly forced his entire helmeted head backwards - violently and abruptly - onto his racing car's head-rest.

Again, using the simple f = m X a equation - and your excellent retort, "mgb_phys", thank you! - I feel Felipe Massa was struck by AT LEAST 440 pounds / feet of energy - a description (pounds / feet) often used to illustrate the energy in a bullet ... because that, essentially, was what the projectile was that impacted him. It simply was not "fired" from a gun.

Kind regards,
 
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A typical modern military bullet weighs around 4g and has a muzzle velocity of around 900m/s so a kinetic energy of 1.7 KJ
A 800g part hitting you at 170mph (76m/s) has a KE of around 2.3KJ.

The helmet spreads the force out over a larger area so does less tissue damage than the bullet but the energy ultimately absorbed by the brain and neck muscles is similar.