PHYSICS Q regarding PE and KE

[Carbon]

Ok when an object is at rest, it has 100% or potential energy and 0% kinetic energy. So would the object have to move at the speed of light to attain 100% kinetic enegy and 0% potential energy? Right? Theoretically? am i bass ackwards on this.

furthermore, that imparting force has to have energy to move the object the speed of light, as a reffrence correct?

[Mister Sinister]

Now when you are saying 100% kinetic energy are you meaning that the object has become pure energy or that the object has attained the maximum amount of kinetic energy possible given its mass and compostion? The problem with any object attaining light speed is that mass increases as velocity increases so to reach the speed of light and infinite amount of energy would be needed. Being light has no mass it gets away with this. If you define the mass and the acceleration of the object and the limits of this you would be able to extract the percentages. I may be wrong on this feel free to correct me as I have never had to take a psyics class to get my BA in history.

[sgt_easton]

Ok when an object is at rest, it has 100% or potential energy and 0% kinetic energy. So would the object have to move at the speed of light to attain 100% kinetic enegy and 0% potential energy? Right? Theoretically? am i bass ackwards on this.

furthermore, that imparting force has to have energy to move the object the speed of light, as a reffrence correct?

It's kind of hard to generalize so much. It's easier to deal with a part of energy, say, gravitational potential and kinetic energy.

Now, the last time I took physics was two years ago - Calculus based Physics III. What a...well....I can't use the proper words here to describe my thoughts on it.

I've never dealt with percentages, but, I guess you can look at it like this - base your percentages off of how fast the object can go. For example, if you drop a ball from the table, it will hit the ground at a small speed. If you drop it from a 100 story building, it will fall faster, but you know that if you drop it from a higher place then it can go ever faster, thus more kinetic and less potential energy. If you drop it from orbit, well, it will fall pretty freakin' fast - and burn up in the atmosphere. I guess you have to determine how fast the object can travel - obviously, nothing can travel at the speed of light (except for light, duh)....well, right now anyway. I bet that will change in our lifetimes; at least the technology will reach the experimental phase.

Also, mass has no impact on the speed an object can travel. It just takes more work to make it go that fast. Galileo proved this.

I wish I could elaborate more, but my physics books were burnt to ashes after I finished thet courses. Blechhh, I'm having bad memories just thinking about it.

[�?�� �m���]

so basically you guys are saying e=mc^2 and if your moving fast enough say c speed of light 3x10^8 m/s you become pure energy

yes sdrawkcab sass


Can i ask why your wondering this when its summer and school is out?

[brianlojeck]

The first thing to keep in mind is that the percentages you are speaking about have nothing to do with the AMOUNT of force involved.

If I am holding a baseball at the top of the empire state building, it has 100% potential energy. If I am holding another baseball 2 feet off the ground, it also has 100% potential energy. Different amount of energy, same %100.

This is the difference:

Kinetic energy is how hard something is flying at you. It's energy of motion. This can be used to do work (hitting somebody witha baseball), generate noise (a drumstick striking a drum), or make heat (as all impact does)

Potential energy is simply a representation of how much kinetic energy something will have when you let it go. This is not a real force, but an estimation of how much force it might output in total.

For example, I carry a baseball up the empire state building. It now has a great deal of POTENTIAL energy. If I toss it off the side all of that potential energy becomes kinetic energy as soon as it reaches ground level in a massive noisy "splat". If I carry it down the stairs the same thing happens, but instead of a big dramatic fall, there are thousands of little tiny kinetic translations as I decend the stairs.

Basically, potential energy means "how much energy was expended to lift something this high in the air, or pull it back against a spring this far."

[Chris42050]

I'm a little lost. What about terminal velocity? You know the maximum speed an object can fall. Wouldn't dropping a ball off the empire state building be the same as dropping it out of a plane.

[�?�� �m���]

terminal velocity depends on height because of the acceleration of gravity and drag, dropping a ball out of a plane would reach its terminal velocity whereas if it was off the empire state building it might not reach the terminal velocity

[brianlojeck]

terminal velocity depends on height because of the acceleration of gravity and drag, dropping a ball out of a plane would reach its terminal velocity whereas if it was off the empire state building it might not reach the terminal velocity

It actually depends on density of the object vs. air resistance. If an object is light (a mouse), wind resistance might balance gravity so quickly that the mouse cannot fall fast enough to kill itself.

I was, however, speaking theoreretically, in a world without air. In the real world a great deal of the empire state building's baseball's energy would be burned off as heat due to air resistance rather then becoming velocity, but the potential/kinetic/thermal/chemical energy equation would still have to balance out in the full round-trip up and down the building.