# Help in explaining formula of Kinetic Energy

## 84 posts in this topic

I can’t think of anything more consistent with the concept of vectors than the distance formula (d = 1/2 v²/a). The ‘a’ in the distance formula is typically gravitational acceleration; and this direction of acceleration is always down. So the ‘a’ in the distance formula has one and only one direction; down.

Except that acceleration might not be constant and the velocity might have a different direction. Claiming that a is "typically" down is a gross simplification, and demonstrates that your deviation is not generally valid. In fact, most of your posts is only valid in very specific situations.

So, while I think your intentions are good, I have to agree with studiot.

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Just to show we all make mistakes this line in post#73

This clearly comes from the correct full formula d = u + 1/2 at2,

Should read d = ut + 1/2 at2,

Your approach will get you into greater difficulty when you come to more advanced dynamics like motion in a circle and impact/collision.

There is no potential energy involved, for instance, when two billiard balls collide on the table, or a bullet hits a target.

gravity is not directly involved.

How does your analysis handle the interchange of KE here?

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V = a*t

a = (V2 – V1) * t

KE = (1/2a) * V^2

Question – what mean the terms square for velocity and one half acceleration?

Thought experiment:

Draw a vector. The period (t) on the vertical axis and the speed (V) on the horizontal.

Assume an acceleration for one second of 10 meters/sec.

The vector speed caused by “acceleration” (a) going from zero at t = 0 to 10 at t = 1.

If you graph this 4 x 4 you can see that the area under the ‘a’ line is half of the area or 2 squares. This area represents the kinetic energy or KE.

If you draw another constant acceleration line at half of the acceleration you will see that the area under this line is ½ square or doubling the acceleration requires four times the energy to achieve the same speed as half the acceleration in the same period of time.

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RiceAWay post#78

1) V = a*t
2) a = (V2 – V1) * t
3) KE = (1/2a) * V^2

Perhaps you would like to clarify these?

I have added the numbering for reference clarity.

Edited by studiot
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@RiceAWay

Since you won't clarify, I will.

1) is incomplete.

2) is just plain wrong since V2 = V1 + at, a = (V2-V1) divided not multiplied by t

3) is also wrong since it implies that kinetic energy is independent of mass, amongst other issues.

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I went through your questions and working in great detail.

Following a complete failure to address even one of my questions, why would you expect me to answer yours?

The above is just a load of waffle.

Actually you totally buried the question. Exactly where did our original poster ask about vector analysis or centripetal force? His question assumed that mass was a part of the equation that he was not interested in.

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Actually you totally buried the question. Exactly where did our original poster ask about vector analysis or centripetal force? His question assumed that mass was a part of the equation that he was not interested in.

If you are going to make claims here it would be wise to ensure their correctness.

The original post was over 5 years ago. some time before I actually joined SF.

I did not in fact join the discussion until recently, when I did indeed offer a novel answer to the OP's question "Where did the half come from" in my post#39.

If you are actually interested to learn anything you might be interested to know that there is another energy formula containing the factor of one half.

Strain energy = 1/2 stress x strain.

This also causes difficulty when folks first meet it.

I think both these difficulties are caused by over emphasis of the formula work energy = force x distance in early learning of physics.

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If you are going to make claims here it would be wise to ensure their correctness.

The original post was over 5 years ago. some time before I actually joined SF.

I did not in fact join the discussion until recently, when I did indeed offer a novel answer to the OP's question "Where did the half come from" in my post#39.

If you are actually interested to learn anything you might be interested to know that there is another energy formula containing the factor of one half.

Strain energy = 1/2 stress x strain.

This also causes difficulty when folks first meet it.

I think both these difficulties are caused by over emphasis of the formula work energy = force x distance in early learning of physics.

It really doesn't matter whether this posting was made 20 years ago or now. Students looking for answers to simple questions get very little from your definition of space/time and relativity. No matter HOW CORRECT you are that totally redirected the question.

It struck me that you were more interested in showing your own understanding of quantum physics than in a simple question. I think that this is the same argument I've had on some of the other strings here. No matter the width and grasp of your own physics, people that are beginning or even intermediate students aren't helped by throwing advanced knowledge at them. All it does is to confuse the issue.

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!

Moderator Note

RiceAWay

Would you be kind enough to stop focussing on criticism of other members' posting style, approach, and abilities and, instead, concentrate on the science and the debate. Too many of your 27 posts seem to be targetted away from the science and towards the posters themselves.

I remind everyone else that if a poster takes a thread off-topic then the best option is to report the post rather than make matters worse by replying to the hijack.

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