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seen Sep 11 at 16:39

May
17
comment Why do we need the quantity momentum?
While it's true that energy can't be created or destroyed, it can end up in forms that aren't useful to us. In a car engine, for example, you use chemical energy in the fuel to give kinetic energy to parts in the engine, but some of the energy turns into heat, which isn't useful. (In fact, most of it ends up as heat; engines are not very efficient.) In introductory physics we often talk about energy "lost" to friction or deformation.
May
15
awarded  Supporter
May
15
comment how to calculate minimum torque a DC motor needs to move the wheels
Minor nit-pick: if friction with the floor is too low, or your torque is too high, you could skid out and have trouble moving because of that. Other than that, good explanation.
May
15
awarded  Critic
May
15
comment Why is a black hole black?
If you're familiar with tensor calculus, John Rennie's answer should be fairly easy to follow.
May
14
awarded  Nice Answer
May
14
answered Why do we need the quantity momentum?
May
14
awarded  Teacher
May
14
answered Why is a black hole black?
May
14
answered Turning an Airplane. What actually causes the circular motion in a banked (roll) turn?