If an object is moving upwards with constant velocity in which upward force is supplying energy and gravity is extracting energy till height ($h$), so from where it gained potential energy?
Please also answer why gravitational potential energy increases with increase in height?
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$\begingroup$ I'm not sure I understand your first question. You should explain your current thoughts or understanding to obtain better answers. However, take a rocket for instance - the 'upward force' comes from what? What gives a rocket the ability to overcome gravity? There is potential energy in a rocket, but it is not gravitational potential. For your second question - gravitational potential only increases relative to a specified point. Drop a book from 1m - before it drops, its potential energy is at a 'maximum' and converts to kinetic energy as gravity pulls it down. $\endgroup$– bleuofblueCommented Mar 10, 2022 at 5:55
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3 Answers
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If you 're pertaining to this sort of example , i think this should be your answer
EG : An object is laid on the ground, it has some potential energy . When I throw it to a higher level , according to the formula of potential energy = mgh ( m-mass, g- acceleration due to gravity , and h- height ) , becuase the height increases , the potential energy increases .
Question is WHY ?
" Energy cannot be destroyed or created it is simply transferred into another form" Ans: When I throw an object to higher level with my hand , my hand gives the object some energy in the form of kinetic energy. As the energy ( kinetic energy) is moving up overcoming the force of gravity, this energy then transfers to the objects potential energy thus increasing the potential energy of the object.
When the object reaches its maximum height , all its left is with potential energy so for a moment only it stays there , and then due to the gravity it accelerates towards the grounds , turning all its potential energy to the kinetic energy .
I hope this clarifies your doubt , If not I suggest you could specify the question for more clarity so that other users can post the right answers for you .
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- If an object is moving upwards with constant velocity in which upward force is supplying energy and gravity is extracting energy till height ($h$), so from where it gained potential energy?
The work-energy theorem states that change in kinetic energy equals total work done on an object
$$\Delta K = W$$
In your case, $W$ is total work done by upward force and gravitational force. Given that kinetic energy does not change $\Delta K = 0$ (object is moving at constant velocity), it gains gravitational potential energy from the work done by the upward force.
- Please also answer why gravitational potential energy increases with increase in height?
Work done by gravitational force equals
$$W_g = -\Delta U = U_1 - U_2$$
where $U = mgy$ is gravitational potential energy, $y$ is the object height and positive $y$ direction points upwards. Which object will gain more kinetic energy - the one dropped from the first floor or the second floor?
Since work is defined as force times displacement, more height means more displacement, and this equals to more work being done by the gravitational force. Hence, gravitational potential energy increases with increase in distance (height) from the Earth.
answered Mar 10, 2022 at 6:16
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I think that your understanding of the concept of potential energy lacks at least two important concepts.
The first is the concept of a system which in this case could be the object or the object and the Earth.
Once you have defined the system you can differentiate between internal and external forces.
Let the system be the object which is moving upwards at constant velocity.
The system is under the influence of two external forces, the gravitational attraction of the Earth downwards and an upward force provided by something, say it is you.
As the object is moving upwards at constant velocity these two forces must be equal in magnitude so the net force on the object is zero and the net work done on the object by the two external forces is zero.
You will note that there was no mention of gravitational potential energy when discussing a system consisting of a single object.
If you want to use the concept of potential energy a system must consist of at least two objects, so let these be the object and the Earth.
Once the system has been defined in that way there are now two external forces acting on it.
You pushing the object up whilst at the same time pushing the Earth down.
The gravitational forces, Earth attracting object and object attracting Earth, a Newton third law pair, are internal forces.
The work that you do in separating the object and the Earth gives the object & Earth system a store of mechanical energy called gravitational potential energy.
What that means is that the system has the capability (potential) of doing more work as the separation between the Earth and the object increases.
Usually because the mass of the Earth is so much greater than than of the object and the Earth moves so little as compared with the object gravitational potential energy is associated with just the object.
For example if you dropped the object it would accelerate downwards whilst at the same time the Earth would accelerate upwards.
So both the object and the Earth gain kinetic energy with the object gaining much, much more.
Indeed, so much more that the gain by the Earth can be neglected.
An example of this stored (potential) energy is, having been raised the object could be attached to the shaft of an electrical generator and whilst it fell, with the gravitational attractive force(s) doing work, electrical energy is produced.
That electrical energy coming from the stored (potential) energy within the object (and Earth) system.
