GPE and Escape Velocity: Understanding the Relationship for Moving Objects

[ahmed emad]

Is it necessary to be the kinetic energy greater than gpe to move ( I don't talk about in orbits)
Example :
Is it will be harder to move an object has a bigger gpe ( same mass but bigger height from ground).
And thanks.

 

[berkeman]

Is it necessary to be the kinetic energy greater than gpe to move ( I don't talk about in orbits)
Example :
Is it will be harder to move an object has a bigger gpe ( same mass but bigger height from ground).
And thanks.

Sorry, but your post does not parse or translate very well. Can you give a practical example of your question with lots of details and maybe a sketch? Thanks.

 

[ahmed emad]

I meant if I increased the gravitational potential energy of object will it be harder to move?

 

[berkeman]

I meant if I increased the gravitational potential energy of object will it be harder to move?

Well, that clears everything up!

Just kidding. You did not address my response -- more details, a sketch, etc.

if you increase the GPE of an object on a table by increasing its mass (by pouring more water into a jug), then it gets harder to move sideways on the table due to the increase in the friction between the table and the jug.

If you increase the GPE of the space station by moving it to a slightly higher orbit, and then fire the thrusters to move it sideways in orbit, then no, it takes no more fuel to execute the maneuver.

See? More details and example about your question would help us to help you with your conceptual question.

 

[ahmed emad]

Increase Gravitational potential energy by the distance from ground not mass

 

[ahmed emad]

If machine lift object where it in 2 meters from ground will be easier than lift it from 5 meters from ground

 

[berkeman]

Is it will be harder to move an object has a bigger gpe ( same mass but bigger height from ground).

Increase Gravitational potential energy by the distance from ground not mass

Then my space station example would seem to apply, no? What is motivating your question? Is there something you have seen in your reading and studying that makes you think otherwise?

 

[ahmed emad]

No I just was thinking about it

 

[ahmed emad]

I will try to make it clear , you have a plane and in time 1 the gpe of it was 20 and in time 2 gpe was 70 because the distance from ground increased , is the plane will be harder to move at time 2 more than time 1?

 

[berkeman]

No I just was thinking about it

Fair enough. Asking questions is a good way to learn. Did my space station example make sense?

 

[ahmed emad]

Unfortunately no.

 

[berkeman]

I will try to make it clear , you have a plane and in time 1 the gpe of it was 20 and in time 2 gpe was 70 because the distance from ground increased , is the plane will be harder to move at time 2 more than time 1?

Bad example. To increase the plane's GPE without increasing its weight, you need to increase its altitude. What 2 effects does that have on it's ability to change its KE? That's a much more complex example, not simplified. Do you see why?

 

[ahmed emad]

So KE of plane not have a relation with GPE?

 

[PeterDonis]

Is it necessary to be the kinetic energy greater than gpe to move

No. An obvious counterexample is an object sitting at rest on Earth. It has zero kinetic energy but nonzero gravitational potential energy; but it can be moved.

if I increased the gravitational potential energy of object will it be harder to move?

Not for that reason, no. See below.

An underlying confusion you might have is that you might be thinking that increasing an object's gravitational potential energy increases its inertia. It doesn't.

If machine lift object where it in 2 meters from ground will be easier than lift it from 5 meters from ground

If you mean, lift vertically, then there is a very, very tiny difference, yes, but it's not due to the change in gravitational potential energy; it's due to the very, very tiny decrease in the force of gravity when you go from 2 meters above ground to 5 meters above ground.

 

[ahmed emad]

I meant increase gpe without changing the force of gravity

 

[PeterDonis]

I meant increase gpe without changing the force of gravity

You can't. To increase your GPE, you have to change either your height, or the mass of the planet you're sitting on. Either one changes the force of gravity.

 

[ahmed emad]

Ok thank you very very much for your help and Excuse me for my sins

 

[PeterDonis]

You're welcome!

 

[rcgldr]

Note that GPE is normally a negative number, using infinity as a reference distance where GPE equals 0. Increasing GPE makes it less negative, and assuming a point source or it's equivalent for gravity, then the force of gravity decreases as GPE increases.

If in a circular orbit, and the goal is to establish a new circular orbit with an increased radius and increased GPE, which optimally takes two bursts of energy to change the velocity, the maximum requirement occurs at a specific ratio of orbital radius:

https://en.wikipedia.org/wiki/Hohmann_transfer_orbit#Worst_case.2C_maximum_delta-v

 

[nasu]

You can change the GPE by just choosing another reference level. Which means by doing nothing to the system. The GPE value is not relevant. Only changes in GPE are meaningful.

 

[russ_watters]

If machine lift object where it in 2 meters from ground will be easier than lift it from 5 meters from ground

No: f=ma does not include a term for GPE.