# In your own personal life, how often do you use this equation?

1. Jul 29, 2008

### eratosthenes2

Thought this would be an interesting topic.

so just in everyday life, what sort of stuff have you applied the tool K = 1/2 mv squared for?

2. Jul 29, 2008

### Staff: Mentor

I'm an engineer who designs heating and air conditioning systems, so I use it or a variation of it a few times a week to calculate fan energy.

3. Jul 29, 2008

### Staff: Mentor

I use it very often in my everyday life, usually for answering PF questions

4. Jul 29, 2008

### brewnog

I use it pretty often, for various engine design and analysis activities.

5. Jul 29, 2008

### Integral

Staff Emeritus
Use it? What do you mean use it? I am aware of it every time I catch or throw something, every time I step on the gas pedel, and again every time I empty my wallet into the gas tank.

How do you want me to use it?

6. Jul 29, 2008

### Ignea_unda

Well, still being a student...classes.

7. Jul 29, 2008

### Jimmy Snyder

Relativity theory homework problems.

8. Jul 29, 2008

### humanino

Like Integral, say for instance when I see a traffic light turning red and there is a huge truck at high speed sticking to my tail, and the road is covered with snow.

9. Jul 29, 2008

### Staff: Mentor

Knowingly? Never.

10. Jul 29, 2008

### Cyrus

No you dont. You think to yourself that truck is coming fast, I better get out of its way. You don't say omg think about the 1/2mV^2....

The truth is no one uses it outside the context of doing a calculation for something they are working on.

The only time I've ever used it outside of a pure calcuation was in understanding the stall characteristics and flight envelope of the airplane I fly by understanding the concept of 1/2mv^2 in terms of the airplane and the airflow.

The only time one would use it is to say, oh I see why this is behaving this way. Its due to the 1/2mv^2.

11. Jul 29, 2008

### humanino

That's not true seriously. I do think about it, whether you like it or not. I do take into account both the weight and the squared speed. It happened to me more than once. Well really, once with the snow, but several times this day ! I would never be confident in those consideration if I did not know the formula.

12. Jul 29, 2008

### Defennder

This reminds me of a joke I read some time back. A physics student was walking underneath a building under construction when a small brick fell from above and struck him senseless. He was rushed to the hospital. When he regained consciousness, he started to smile to himself, much to the worry of his family members visiting him. He explained, "Luckily kinetic energy is only half mv squared".

13. Jul 29, 2008

### OmCheeto

I used it a while back trying to solve the worlds energy crisis. pe = mgh = ke = 1/2 mv^2.

Recouping an automobile's kinetic energy in braking by converting it to potential energy turned out to be a not so wise solution.

Cars would have to be elevated to something like 50 feet in the air to store all that energy from 50 mph to zero.

I think it would make a good Dr. Seuss episode though.

14. Jul 29, 2008

### Cyrus

Well, then your weird my friend, not that theres anything wrong with that...

(PS, I dont know why you would think about that. I'd rather be thinking about F=mu*N (frictional braking), but hey.)

15. Jul 29, 2008

### humanino

That's clear :tongue2:
But you see, now next this happens, I'll think about the balance between F=mu*N and E=1/2 mv2, for sure. Thanks

16. Jul 29, 2008

### Cyrus

Actually, when I'm driving I'll get pissed if the light changes on me and I have to slow down quickly because it wastes all that kinetic energy I had. The transients in driving is the most inefficient parts. I hate going 50mph and then have to come to a dead stop because the light changed on me quickly. I time it so when I know its going to turn red I let the car slow down via coasting so I only have to use the brakes very lightly to come to a dead stop.

But again, im thinking 'energy' not '1/2mv^2'

17. Jul 30, 2008

### OmCheeto

Have I slipped into an alternate universe? I thought 1/2mv^2 was energy?

Ok. Don't mind me.

Did you ever notice that the m's cancel out in the two equations?

So bicyclists and runners would have to have some sort of Goldbergian scissor-jack devices installed in their frames and shoes to recoup their energies as well.

Did I ever tell anyone about the time I figured out how many coil springs it would take to recoup an automobiles energy from 50mph to zero? It was not a pretty number.

But yes eratosthenes2, as I said before, I think about 1/2.., and many other equations all the time.

18. Jul 30, 2008

### Cyrus

19. Jul 30, 2008

### OmCheeto

:rofl: :rofl: :rofl:

sorry...... I'll just tip-toe off to bed now.........

20. Jul 30, 2008

1/2 m what?