Register to reply

GPE and KE...please help argh

by meawinner
Tags: argh, keplease
Share this thread:
meawinner
#1
May4-04, 10:42 AM
P: 11
Hi I am just finishing my AS physics coursework and just as i thought i understood it someone tells me something else. When you pick up an object i understand that it gains GPE and the amount of this depends on the height it is picked up to, hence GPE = mgh. But when you drop the object what happens to the energy? Does it all suddenly convert to KE, or when it is falling does the GPE gradually turn to KE?

In my coursework i calculated GPE and KE, assuming they should be roughly the same values and they were but then some1 said to me that they should be inversely proportional to each other.

Can some1 please help me thank-you.

meawinner
Phys.Org News Partner Physics news on Phys.org
Physical constant is constant even in strong gravitational fields
Physicists provide new insights into the world of quantum materials
Nuclear spins control current in plastic LED: Step toward quantum computing, spintronic memory, better displays
Dr Transport
#2
May4-04, 11:24 AM
Sci Advisor
PF Gold
P: 1,481
just think about conservation of energy. when the object is falling, the height changes, by virtue of energy conservation, the object gains kinetic energy.
quantum mechanic
#3
May4-04, 12:35 PM
quantum mechanic's Avatar
P: 11
If you lift a ball to some heigth h, you obtain a potential energy due to gravity that is equal to mgh. When the ball drops, the energy is gradually converted to KE, not all at once. To emphasize this point, imagine dropping the ball from heigth h. A friend catches the ball at height h/2. Since we already know the formula for potential energy due to gravity, our new potential would be equal to mgh/2. The ball still maintains an energy potential that was not converted to kinectic. All the potential energy is converted to kinetic energy at a time (only at the instantaneous moment right before impact) when h=0 after the point of release.

arildno
#4
May4-04, 12:51 PM
Sci Advisor
HW Helper
PF Gold
P: 12,016
GPE and KE...please help argh

Quote Quote by meawinner
In my coursework i calculated GPE and KE ....
some1 said to me that they should be inversely proportional to each other.
meawinner
As are implied by Dr Transport's and quantum mechanic's replies, the conversion of potential energy into kinetic energy (or vice versa in other situations) is a gradual process.

When we have energy conservation, it means that the SUM of kinetic energy and potential energy remains equal at all times.

Those who told you that the kinetic energy should be inversely proportional to the potential energy are totally wrong; they haven't learnt the elementary distinction between a sum and a product.
Integral
#5
May4-04, 02:59 PM
Emeritus
Sci Advisor
PF Gold
Integral's Avatar
P: 7,337
The sum of the energys must remain constant. (this is a no loss system of course!)

So Total Energy = Potential Energy + Kinetic Energy

This is true at each point of the fall.


Register to reply

Related Discussions
General GRE-argh! Academic Guidance 12
Argh RE kills me. General Discussion 2
Trying to factor a polynomial General Math 0
Masterphysics again, ARGH! Introductory Physics Homework 1
ARGH Bad night! General Discussion 5