Calculating Force and Time with Impulse: When and How?

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    Impulse
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Discussion Overview

The discussion revolves around the concept of impulse in physics, particularly its application in scenarios involving large forces acting over short durations. Participants explore how impulse relates to force and time calculations, and its relevance in specific contexts such as collisions and model rocketry.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification

Main Points Raised

  • One participant questions the instances in which impulse is used and how it aids in calculating force or time.
  • Another participant explains that impulse is utilized when the force or time does not need to be calculated, emphasizing its relationship to momentum.
  • A classical example of impulse is noted in the analysis of collisions.
  • A participant shares a personal experience with model rocketry, highlighting how total impulse from rocket engines can be used to estimate launch speed and trajectory despite varying thrust during the burn period.

Areas of Agreement / Disagreement

Participants present multiple perspectives on the use of impulse, with no consensus reached on a singular approach or understanding of its applications.

Contextual Notes

Some assumptions about the definitions of impulse and momentum are not explicitly stated, and the discussion does not resolve the complexities involved in calculating force and time from impulse.

mahela007
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In what kind of instances would the quantity of impulse be used? My textbook says that it's when very large forces act for very short times but how would that help us calculate the force OR the time?
 
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It is precisely when we cannot or do not need to calculate the force or the time for which it acts that we use the concept of impulse. The impulse is the integral of the force with respect to time and can be proved to be equal to the change in momentum. Here are some good sites for preliminary reading:

http://id.mind.net/~zona/mstm/physics/mechanics/momentum/introductoryProblems/momentumSummary2.html
http://www.glenbrook.k12.il.us/gbssci/phys/Class/momentum/u4l1b.html
 
Last edited by a moderator:
A classical example is in the analysis of collisions.
 
When I was in school, I was "into" model rocketry for a while. Solid-fuel model rocket engines were rated in terms of the total impulse they produced, between ignition and burnout. The actual thrust (force) exerted varied widely during the burn period, but the burn period was short enough that you could use the total impuse to calculate good estimates of launch speed, maximum height of trajectory, etc.
 
Thanks
 

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