Gpe (1 Viewer)

[speed_bump]

Can anyone help me with gravitational potential energy? In the excel book it is defined as "a measure of the work done in moving an object from infinity to a point in the field". I don't really understand this at all. How can it be at infinity when the gravitational field is equal to the inverse square of the distance?

Thanks

 

[Lazarus]

Originally posted by speed_bump
How can it be at infinity when the gravitational field is equal to the inverse square of the distance?

Infinity is just a point so far away from the gravitational source that the field may as well be equal to zero (think of it as a limit).

The definition is set out in this way so that as an object moves away from the gravitational source (e.g. the Earth) the potential energy increases until it reaches the value of zero at infinity. This is also the reason for the minus sign in the corresponding equation.

 

[Rahul]

yep, make infinity a limit. try this trick with limits(esp in maths), try calculating 1/1000000 (1 divided by a realy large number(~infinity for arguments sake). it is nearly zero. now make the denominator 50000000. u will find that it would be closer to zero as u get closer to infinty. so wen u reach infinty, which does not really exist, there will b no affect of the gravity.

the gravitational force of the earth is in (<--) direction. this is taken as +ve. now work done to move something in (-->) would be in the opp dircetion to the gravity. this is why it is negative.

hope that clears it up somewhat. correct me anyone if i am wrong.