Law of conservation of kinetic energy?

In summary, the law of conservation of energy states that energy cannot be created or destroyed, but can only be transferred or transformed from one form to another. This applies to both chemical and kinetic energy, where the initial energy must equal the final energy. However, for kinetic energy, it is not always conserved in collisions, as seen in the example of two blobs sticking together and losing all kinetic energy. In order to prove conservation of energy, calculations involving elastic potential energy and the spring constant (k) are necessary. The spring constant is a measure of how tough a spring is and is usually given or can be found in physics handbooks.
  • #1
Dynamite
28
0
Is there a difference between the "law of conservation of energy" and "law of conservation of kinetic energy?" If so what is it?

and what IS the law of conservation of kinetic energy? It doesn't seem to be in my textbook or on the net..
 
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  • #2
That's because it doesn't exist. Kinetic energy is not conserved. Two blobs of equal mass hit at equal velocity and stick together. The resulting blob has no kinetic energy. Poof. Kinetic energy all gone.
 
  • #3
o dear. sigh. I have a lot more to worry about now
thanks
 
  • #4
Here is an example of the conservation of energy.

Say a bomb explodes. Initially, the bomb has chemical energy. When it explodes, the types of energy present are heat,light and sound. But energy neither made or destroyed, so it had to come from the chemical energy.
So applying the law of conservation of energy, you'd say that
Chemical energy -> heat+light+sound

For kinetic energy. If two bodies collide and kinetic energy is conserved, then the kinetic energy before impact =kinetic energy after impact. Kinetic energy is conserved in elastic collisions.
 
  • #5
ok ok hold on, my question here is though
I have 2 carts with springs at the back of them and I've pushed them together and realeased
Then in order to prove that energy has been conserved, I'd need to calculate the elastic potential energy right..?
 
  • #6
Yes. Total energy is conserved. The initial elastic potential energy must equal the final kinetic energy.
 
  • #7
o goodness. Yes I DO have a lot more to worry about.
Which means I need to find the spring constant.
What does the K mean? in F=k delta x ? Is there a way I can find x with info only about force? I'm not sure I even have k...
 
  • #8
Dynamite said:
o goodness. Yes I DO have a lot more to worry about.
Which means I need to find the spring constant.
What does the K mean? in F=k delta x ? Is there a way I can find x with info only about force? I'm not sure I even have k...


The K is the spring constant. In F=kx, F= force, x=displacement, and k=the spring constant
 
  • #9
Dynamite said:
o goodness. Yes I DO have a lot more to worry about.
Which means I need to find the spring constant.
What does the K mean? in F=k delta x ? Is there a way I can find x with info only about force? I'm not sure I even have k...

I think you'd better state the full problem you are working on.
 
  • #10
Hahaha. On the Standardize test last year, they actually have that as the right answer. (because the other answers definitely didn't make sense at all). Heh.k is known as the string coefficient. It is a constant that every spring has. Think of it this way...

IF I were to pull on a slinky..it would be pretty easy to stretch it. So the k value would be small. If I were to pull a car spring (made of steel and all), I wouldn't be able to do it. So the k value would be big.

It is essentially a value that take into account how tough your spring is..and adjust the force necc to stretch it appropriately.

Spring constant are usually given. In some situations, you might set up a conservation of energy (PE --> KE or vice versa) to solve for k...then calculate x, F (which ever is not known)

In reality, you can prob look up the K value online or in some physics handbook if you are doing a lab and need that value
 

1. What is the law of conservation of kinetic energy?

The law of conservation of kinetic energy states that the total amount of kinetic energy in a closed system remains constant over time. In other words, energy cannot be created or destroyed, but it can be transferred from one form to another.

2. How does the law of conservation of kinetic energy apply to everyday life?

This law is applicable to many everyday situations, such as a swinging pendulum or a rolling ball. In both cases, the kinetic energy of the object is constantly being transferred between potential energy and kinetic energy, but the total amount of energy remains the same.

3. Does the law of conservation of kinetic energy apply to all types of energy?

No, this law only applies to kinetic energy, which is the energy an object possesses due to its motion. Other forms of energy, such as potential energy or thermal energy, are subject to different laws of conservation.

4. Can the law of conservation of kinetic energy be violated?

Under normal circumstances, this law is always valid. However, in certain extreme situations, such as nuclear reactions or particle collisions, the law of conservation of kinetic energy may not hold true due to the conversion of energy into mass.

5. Who first discovered the law of conservation of kinetic energy?

The law of conservation of kinetic energy was first formulated by German physicist Julius Robert von Mayer in the mid-19th century. It was later refined and popularized by other scientists, including James Prescott Joule and Hermann von Helmholtz.

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