Basic kinematic physics equations do not make sense to me.

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    Kinematic Physics
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Discussion Overview

The discussion centers around the application and understanding of basic kinematic physics equations, particularly in the context of free fall. Participants explore the implications of these equations, their accuracy in real-world scenarios, and the effects of perception and measurement on the interpretation of results.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Exploratory

Main Points Raised

  • One participant calculates the distance a ball falls in 2 seconds using the equation ΔX = ViT + 1/2AT^2 and arrives at 19.6 m, expressing disbelief in this result based on personal observation.
  • Another participant suggests improving the accuracy of the test to validate the calculations.
  • Some participants argue that the equations are valid and that misperception may affect the understanding of the fall time, noting that there is a delay in registering the impact.
  • One participant challenges others to conduct a practical test by dropping an object from a height of 20 meters to observe the fall time directly.
  • A participant mentions that SUVAT equations do not account for air resistance, implying that in a vacuum, the equations hold true.
  • There is a request for clarification on what SUVAT equations are, with a subsequent explanation provided by another participant.
  • Some participants express skepticism about the duration of a 2-second fall, comparing it to falling from a height that could be dangerous.
  • Another participant reiterates that the equations reflect reality on a classical level and suggests a practical experiment involving a ball rolling down a ramp to demonstrate the principles accurately.

Areas of Agreement / Disagreement

Participants do not reach a consensus; there are multiple competing views regarding the validity of the kinematic equations and their applicability to real-world scenarios. Some participants defend the equations, while others express skepticism based on personal experience.

Contextual Notes

Participants highlight potential limitations in measurement accuracy, the influence of air resistance, and the subjective nature of perception in understanding free fall dynamics. There is also an acknowledgment of the need for practical experimentation to validate theoretical claims.

zeromodz
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If I drop a ball, how far will it fall in 2 seconds?
ΔX = ViT + 1/2AT^2
ΔX = (0)(2) + 1/2(9.8)(2)^2
ΔX = 19.6 m

I tested this, and there is no way an object falls 19.6 m in only 2 seconds. Think about it. Drop something right now and it will only fall like 1 meter in one second. I don't understand. These equations don't fit reality to me. Can someone show me what I am doing wrong?
 
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Yea make your test more accurate.
 
The equations are fine.
One answer is misperception. When the object lands it takes the brain at least 200ms before you register that the object hit the ground. And some more time before you hit the stop watch again.
 
Don't "think about it", just go up 20 meters and drop something. See how long it takes, then come back with the results.

You have to be willing to set aside what you "think" and be open to other possibilities.
 
SUVAT equations don't take into account air resistance, so strictly an object will take 2 seconds to fall that distance in a vacuum.

Also, given that the object accelerates at 9.8ms-2, after one second of falling it will have a velocity of 9.8ms-1, so it will be traveling quite quickly after two seconds and hence of covered quite a distance. I believe it makes more sense if you consider it that way.
 
What is a SUVAT equation?
 
I certainly wouldn't want to free fall for 2 seconds. That's like a fall from a 5 story building...splat. 2 seconds is longer than you think. Try throwing a ball straight up in the air as high as you can and count how long it takes to fall back down.
 
Phyisab**** said:
What is a SUVAT equation?

SUVAT equations are equations like you mentioned at the beginning of the thread, such as
s = ut + 1/2at^2 , or v = u + at. They are named SUVAT equations because they all contain either the terms s, u, v, a or t.
 
The equations are straight forward
and very self explanatory, i don't see
a problem with it...
 
  • #10
There is no problem with those equations. They reflect reality on a classical level just fine.

zeromodz said:
If I drop a ball, how far will it fall in 2 seconds?
ΔX = ViT + 1/2AT^2
ΔX = (0)(2) + 1/2(9.8)(2)^2
ΔX = 19.6 m

I tested this, and there is no way an object falls 19.6 m in only 2 seconds. Think about it. Drop something right now and it will only fall like 1 meter in one second. I don't understand. These equations don't fit reality to me. Can someone show me what I am doing wrong?

Trust me an object dropped will travel much farther than a meter in one second. If you really want to test this out, try doing something compared to what Galileo did by having a ball roll down a ramp. You can much more easily time how far the ball has moved because the ball is moving with an acceleration smaller than g. You will find that the times you get will be in perfect harmony with those kinematic equations
 

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