• 0:00 - 0:04
Now I confess, I've been oversimplifying it because we haven't talked about friction.
• 0:04 - 0:08
Now even though energy can never ever be created or destroyed,
• 0:08 - 0:12
friction in a way removes energy from a system.
• 0:12 - 0:16
Now what do I mean by that. Well before we ??? let's say a ball dropping from some height.
• 0:16 - 0:20
Well, we can think of this as energy converting from gravitational potential
• 0:20 - 0:23
to a kinetic energy as it moved in.
• 0:23 - 0:27
All of the gravitational I want to connect, but in reality that's not what happens.
• 0:27 - 0:31
All of the gravitational potential energy does not get convert to kinetic energy.
• 0:31 - 0:35
How did friction do this? How does it remove energy if energy can't be created or destroyed?
• 0:35 - 0:38
Well before when we look at, let's say a block sliding down a plane.
• 0:38 - 0:42
We visualized this as gravitational potential energy
• 0:42 - 0:46
getting converted to kinetic energy as the block moved down, but let's think about that.
• 0:46 - 0:49
As this blocks slides down, it's rubbing against this plane.
• 0:49 - 0:55
Go ahead and rub your hands together for a second and do it really hard.
• 0:55 - 1:00
They get really hot. In fact, friction creates heat. This heat is another form of energy.
• 1:00 - 1:04
• 1:04 - 1:09
some of it gets converted to useful kinetic energy, but some gets lost as heat.
• 1:09 - 1:15
The energy is still there, it's just that we can't really use it anymore. It's lost as heat to the atmosphere.
• 1:15 - 1:21
Now depending on the material of this plane or other situational factors, the fraction of this energy
• 1:21 - 1:24
that gets converted to heat can change,
• 1:24 - 1:27
maybe a lot of this energy gets converted to heat maybe almost none of it.
• 1:27 - 1:29
So let's consider these three cases.
• 1:29 - 1:34
In the first case, we have an object falling and let's say it's falling to what's called vacuum
• 1:34 - 1:37
so there's no air, it's just falling through empty space
• 1:37 - 1:41
Another example of object sliding down this rough jagged surface.
• 1:41 - 1:44
Another we have an object sliding down a relatively smooth surface.
• 1:44 - 1:50
What I want to know is, which of this diagrams corresponds to which of this pictures.
• 1:50 - 1:53
So in this diagram all of the potential energy is getting converted to kinetic energy
• 1:53 - 1:59
and here most of it is getting converted to heat, but in here only a small portion gets converted to heat.
• 1:59 -
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Team:
Udacity
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PH100 - Intro to Physics
Duration:
02:03