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### Course: Class 11 Physics (India)>Unit 10

Lesson 6: Conservation of energy

# LOL diagrams

David shows how LOL diagrams allow us to visually represent what we mean by conservation of energy as well as what we mean by an energy system. Created by David SantoPietro.

## Want to join the conversation?

• I thought LOL meant "Laugh out loud.."
• Lots of people do, that's why he clarified in the video ;D
• What does LOL means?
• LOL does not stand for anything. The shapes that we draw when we create an LOL diagram is in the shapes of the letters L, O, and L.
Hope this helps!
• If a an object is sitting on the ground, it has zero Ug (assuming we've establish that ground level as 0). If a sink hole opens up under the object, the object will fall and have Kinetic energy due to gravity, but where did it get it from? Do we change the reference point after the fact to say that the new resting place of the object is now 0 and the original ground was actually X (whatever the height was in relation to the new 0) ? What if, a few minutes later, the ground opens up again and the object falls farther?
I guess what I'm asking is how do we deal with a changing frame of reference? Esp when it comes to defining Ug.
• This used to confuse me too.
The important thing to recognize here is that "energy" is not an absolute amount. It's always relative between 2 different states of the object in question. So when the ball is on the table, you'd say it has 0 gravitational potential E relative to it being on the table surface. But it could have potential E relative to it being on the ground. You have to be comparing 2 states the object is in. (This is usually implied rather than stated explicitly)

Another example: When a moving ball "has kinetic E", it's usually meant in relation to if it were stationary on the floor. So the velocity you care about is the relative velocity between the ball and the floor. But if you zoomed out and considered the ball's kinetic E with respect to the sun (i.e. compared to if the ball were sitting stationary on the sun), the ball would have kinetic E of the Earth's movement as well. So the velocity you care about is the relative velocity between the ball and the sun.

You pick the reference point based on what objects are relevant to the question.
• What would happen if the force of the spring was so great that the mass flew into the air? Would it change the outcome or would it stay the same?
• The mass would probably fly into the air but that doesn't matter for our purposes. When drawing the diagram, we only care about the initial and final positions. It doesn't matter if something happens afterwards.
• Say someone is bungee jumping, and the problem wants to know how much energy is transferred to the cord at the bottom of their jump. How would you solve this problem?
• Depending on the conditions given in the question, either directly use the formula for elastic potential energy or calculate the change in gravititational potential energy (given air resistance is negligible). I'm not too sure though.
(1 vote)
• What is the energy conversion for an object falling through the air at terminal velocity?

(I was asked this question at school, and I answered that gravitational potential energy changes to kinetic. However, my teacher disagreed: GPE won't change to kinetic energy at all, because the object is moving at a constant velocity. This can't be true, as all objects in motion should have some kinetic energy (E = 1/2 mv^2).The _v_ in the formula shows that kinetic energy must be present if velocity is not zero.)
• At terminal velocity the drag force from the air is equal to the gravitational force on the object so the net force is zero so the work done by gravity is also zero so kinetic energy doesn't change.

For example a standard baseball is about 145 g or 0.145 kg and has a terminal velocity of about 33 m/s so it has a kinetic energy of Ek = 0.145 * 33^2 = 0.145 * 1089 = 157.9 J.

So as the baseball accelerates from 0 to 33 m/s it will gain kinetic energy but when the velocity stops increasing the kinetic energy stops increasing as well.

The GPE is getting transferred to other things like sound, heat and turbulence in the air.
• Why is it shown as Ug and Ue We Our teacher showed it as Eg and Ee. Is there any difference or does It mean the same thing?
• I'm pretty sure the more common version is U to stand for potential energy, and to have Ug be gravitational and Ue to be electric.
Eg and Ee would mean the same thing. If your teacher prefers it and you feel like using U, you should ask them just to make sure that they accept both ways of writing it.