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- [Voiceover] Two blocks are connected by

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a string of negligible mass that passes

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over massless pulleys that turn with

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negligible friction, as shown in

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the figure above, we see that there.

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The mass m2 of block 2 is greater

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than the mass m1 of block 1.

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The blocks are released from rest.

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So let's just really quick think about

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what we think is going to happen here.

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Block 2 has a larger
mass, they're connected

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by this string and pulley system here.

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Well if it has a larger
mass, they're in the

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same gravitational
field, it's going to have

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a larger weight and so the weight

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pulling down on block 2 is going to be

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larger than the weight
pulling down on block 1

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and so you're going to have block 2

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accelerating downwards, you're going

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to have block 2 accelerating downwards

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and block 1 is going to accelerate upwards

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with the same magnitude.

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So block 1 is going to accelerate upwards

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and so with that just intuition

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of what we think is going to happen here

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let's try to tackle part A of this.

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So they tell us the
dots below, these dots,

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represent the two blocks, so this

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represents block 1,
this represents block 2.

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Draw free-body diagrams
showing and labeling

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the forces, not components,
exerted on each block.

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Draw the relative lengths of all vectors

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to reflect the relative
magnitudes of all forces.

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Alright, so let's think about what are

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all the forces acting
on each of these blocks.

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Well for each of these blocks you're going

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to have the force of gravity, you're going

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to have the weight of the
blocks acting on them,

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so for example this first block m1,

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m1, and I'll draw it here first,

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what is the force of gravity going to be?

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The force of gravity is going to be

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its mass times the gravitational field.

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Now what is going to be the
force of gravity on block 2?

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Well it's going to be larger than that

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so let me just draw it like this,

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so the force of gravity is going to be

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m2 times g, how did I know
it was going to be larger?

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Well m2 has a larger mass and we are

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in the same gravitational field.

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Now we're not done there, no not done yet

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because now we also have the upward

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pulling force of the tension in the string

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and we could think
about what the magnitude

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of that, we know that the, we know that

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the tension is going to be pulling upwards

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on both of the blocks
but let's think about

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what its magnitude is going to be.

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In order for block 1
to accelerate upwards,

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which is in our intuition
as to what would happen,

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the tension, the force of the tension

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has to be larger, the
magnitude of the tension

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has to be larger than the
magnitude of the weight.

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Now in order for block 2
to accelerate downwards

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the magnitude of the
tension has to be less than

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the downward force of gravity, the upward

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force of tension has to be less than

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the downward force of gravity.

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So the magnitude of the tension

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is going to be inbetween the magnitudes

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of these two weights, so let me draw that.

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So the magnitude of the
tension is going to be

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larger than m1g but smaller than m2g,

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so maybe like that, so
that is tension right there

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and, whoops, and you're going to have

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on this side you're going to have the same

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magnitude of your tension pulling upwards

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but it's now less than the weight,

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which means that the block is
going to accelerate downwards

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and we know that these two tensions,

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the magnitudes of these tension vectors

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are going to be the same because of

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the magnitude of the tension throughout

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this entire string is
going to be the same.

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When you think about
tension, this pulling force,

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you can think about what's happening at an

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atomic or a molecular level
is these are the, you know

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the covalent bonds pulling on each other

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at an atomic level
throughout the entire string

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and when we look at it on a macro level

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we view that as tension.

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So there you have it, I've drawn

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the forces on them but I haven't

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drawn them in the right place,

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I need to draw them on this,

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I need to draw them right over here.

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So let me draw that, I can actually

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draw a little bit more precisely

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because they gave us these lines.

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So on block 1 I have the weight

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so that is m1g,

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I also have the tension,

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I'll make that two of these lines tall,

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so I also have the tension.

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Now block 2 I have the same tension

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or same magnitude of tension I should say,

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now it's also pulling upwards, so tension,

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and I have its weight, which is going

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to be larger than the tension,

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so its weight, I'll make
it three of these lines.

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The way I've drawn it m2 would have

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to be three times, m2 would have to be

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three times larger than
m1 the way I've drawn it.

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They don't tell us that, they
tell us that m2 is larger

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so this seems to be right.

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And we just want to get our intuition here

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since our tension, our upward force

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is larger than our downward force

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you're going to have a net upward force,

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which is going to accelerate block 1 up

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and here you're going to
have a net downward force,

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which is going to accelerate block 2 down,

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which is in line with our intuition

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because block 2 weighs more than block 1.