# Kinetic energy question. (layman)

1. Apr 11, 2013

### Moris526

Hi all.
English is not my native language, so bare with me (joke i found googling the right word). Im from Argentina.
My question.

If i throw a ball, i have learned it has kinetic energy. But if motion is relative doesnt that mean that my hand has the kinetic energy too?

thanks.

Last edited: Apr 11, 2013
2. Apr 11, 2013

### A.T.

Yes.

3. Apr 11, 2013

### Staff: Mentor

I think you omitted a word in the area that I put in boldface. My (your) what has?

4. Apr 11, 2013

### Moris526

Sorry. Yes, I omitted the word ¨HAND¨.

5. Apr 11, 2013

### CAB12

Kinetic energy is a property of anything in motion. The term kinetic means motion.

6. Apr 12, 2013

### Moris526

I dont get it. If anything in motion has kinetic energy and motion is relative then the kinetic motion of an abject is relative? if an object passes me by it has kinetic energy but if i move with it, it does not?

Confused here!.

7. Apr 12, 2013

### A.T.

Yes.

8. Apr 12, 2013

### Mentalist

Hand has kinetic energy ball does not, it isn't moving. Only thing the ball has is internal energy.

Ball thrown, thus has kinetic energy. What matters here is the direction you are throwing it, up, down, left, or right? That would be the reference frame.

Relative motion = you on a plane moving.

9. Apr 12, 2013

### A.T.

10. Apr 12, 2013

### CompuChip

Just to be clear: you are talking about after the ball was thrown, right? Or do you mean while throwing the ball?

11. Apr 12, 2013

### Moris526

Yes, after.

12. Apr 12, 2013

### Moris526

Wikipedia " In physics, the kinetic energy of an object is the energy which it possesses due to its motion.[1] It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity"

Where is the kinetic energy? If it is in the object and comes from an acceleration, that is in relation to a frame of reference, right?. So the object has a diferent kinetic energy in diferent frames of reference? Or it has kinetic energy from a frame of reference?

13. Apr 12, 2013

### MostlyHarmless

That is in part correct. Relative to you running it has less kinetic energy than if you were standing still, that is: If I throw a ball at you at 10m/s and it hits you while you're standing still, then I throw the same ball at you at the same speed, but this time you are running away at 5m/s. The ball has the same amount of kinetic energy in both instances, but getting hit with the ball in case one will hurt more than getting hit by the ball in case 2.

14. Apr 12, 2013

### Moris526

If i measure the energy of the ball as it is approaching me, don't i get different ones? If this is true, the total energy of an object is not absolute?

15. Apr 12, 2013

### Staff: Mentor

Exactly. It is relative.

16. Apr 13, 2013

### CompuChip

Yes, correct: