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1. Draw below a free body diagram for each
mass. Be sure to include all the
forces acting on the mass including friction.
Note: you may print this
pre-lab out and use a pencil or pen to draw on the paper the two free body
diagrams. (Everything else should have been typed in before you print this out.) |
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2. Assume the blocks are at rest. Write down Newton’s second law for all
three components that matter. |
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OVER ŕ |
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3. Using these three equations in question 2,
solve for the static friction force. |
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x component of
the sum of the forces on the block gives the relation |
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Now use the
hanging mass equation |
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Substitute that
in and Static friction is |
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4. What is the maximum static friction force? |
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We can plug in N from above |
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5. If you plotted the maximum possible static friction
force (y-axis) vs. the normal force (x-axis), what would the slope of that
line equal? |
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By comparison with y = mx +b,
the slope is µs |
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6. Now
assume the blocks are moving, so we have kinetic friction, what is the
kinetic friction force? |
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This is true always for
moving objects. |
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7. If you plotted kinetic friction force vs. the normal force,
what would the slope of that line be? |
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By comparison with y = mx +b,
the slope is µk
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