GpE does equal -Ek in the vertical but not the horizontal in a uniform field. So if I threw a ball in the air it's Ek given by virtue of its speed is 'stored' in the gravitational filed. So if the ball is at 20% of its height ek>mgh at 100% all the energy kinetic is stored as gravitational potential so at that point ek=0 and mgh = the ek at the bottom. (assuming no air resistance etc etc)
Having said this throwing something horizontally such that it follows a parabolic path only the Ek in the vertical can be compared to mgh. if it has a velocity on 10ms^-1 forward this cannot be used to find out anything about mgh because it doesn't cause a change in height. The vertical doesn't effect what happening horizontally and vis versa.
Something that confused me was satellites orbiting our planet, they travel across the sky and don't fall to earth so its like they have a horizontal velocity and yet we can equate this to mgh. This is because the Force that provides the acceleration to change direction as the satellites falls missing the earth comes about due to centripetal force witch is in turn a resultant on the gravitational attraction. It can be said that the the velocity the satellite has in its circular path is a result of the force of gravity between the objects and so the two can be equated.
I don't know if that's an answer to your question and i've probably just made things more confusing. Good luck with whatever it is
Having said this throwing something horizontally such that it follows a parabolic path only the Ek in the vertical can be compared to mgh. if it has a velocity on 10ms^-1 forward this cannot be used to find out anything about mgh because it doesn't cause a change in height. The vertical doesn't effect what happening horizontally and vis versa.
Something that confused me was satellites orbiting our planet, they travel across the sky and don't fall to earth so its like they have a horizontal velocity and yet we can equate this to mgh. This is because the Force that provides the acceleration to change direction as the satellites falls missing the earth comes about due to centripetal force witch is in turn a resultant on the gravitational attraction. It can be said that the the velocity the satellite has in its circular path is a result of the force of gravity between the objects and so the two can be equated.
I don't know if that's an answer to your question and i've probably just made things more confusing. Good luck with whatever it is
Original post by Lauren-x-
Is this a follow-up question from an exam/practise question? It may help to have some context, but in most cases it's what the user above said 
i did a experiment known as 'hot wheels experiment' i had to calculate the GPE and Ek of the experiment. i put the results in a table and the calculations don't equal each other, so the answer is no, but i don't know why the answer is no
Original post by syeds
i did a experiment known as 'hot wheels experiment' i had to calculate the GPE and Ek of the experiment. i put the results in a table and the calculations don't equal each other, so the answer is no, but i don't know why the answer is no
Is the hot wheels track a loop da loop? if so then the Gpe at the top will be 2mgr where r is the radius of the loop
Original post by lowkey-loki
Is the hot wheels track a loop da loop? if so then the Gpe at the top will be 2mgr where r is the radius of the loop
there was no loop in my experiment...
Original post by syeds
there was no loop in my experiment...
oh... forget what i said it's not relevant. sorry :L
It'd be because there would be energy lost as heat due to friction between the wheels of the car and the surface of the track.
So if it was a downwards slope with the car starting at the top and then rolling down, some of the GPE energy would be transferred into heat energy due to friction between the wheels of the car and the surface of the track, meaning that less would be transferred into kinetic energy. Hence, GPE would not equal Ek
So if it was a downwards slope with the car starting at the top and then rolling down, some of the GPE energy would be transferred into heat energy due to friction between the wheels of the car and the surface of the track, meaning that less would be transferred into kinetic energy. Hence, GPE would not equal Ek
Original post by syeds
why does GPE not equal Ek???
Gravitational potential energy can equal The kinetic energy once an object of mass which was at a datum point in a gravitational field previously moves down or up. It would then convert all the negative GPE to Ek. But there is also the fact that energy can be lost(transformed into different forms of energy). Maybe this is why the GPE before does not equal the Ek after.
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Original post by Lauren-x-
It'd be because there would be energy lost as heat due to friction between the wheels of the car and the surface of the track.
So if it was a downwards slope with the car starting at the top and then rolling down, some of the GPE energy would be transferred into heat energy due to friction between the wheels of the car and the surface of the track, meaning that less would be transferred into kinetic energy. Hence, GPE would not equal Ek
So if it was a downwards slope with the car starting at the top and then rolling down, some of the GPE energy would be transferred into heat energy due to friction between the wheels of the car and the surface of the track, meaning that less would be transferred into kinetic energy. Hence, GPE would not equal Ek
Thanks!
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