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Lesson 4-5d Everyday Forces

Static EquilibriumHomework

Complete the chapter 2 examination inHomework Helpers: Physics.

Check Moodle for additionalassignments from this section.

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Lesson 4-5d Everyday Forces

Static EquilibriumSection Objectives

Apply the concepts of static equilibriumto problem-solving.

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Lesson 4-5d Everyday Forces

Static Equilibrium

Static Equilibrium representsthe state of an object

at rest, with a net force of zero

acting on it.

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Lesson 4-5d Everyday Forces

Static Equilibrium

Static Equilibrium, or

statics problems arean application ofNewtons second law,because if an object is

not accelerating, thereis no unbalanced forceacting on it.

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Lesson 4-5d Everyday Forces

Static Equilibrium

View the movie by clicking on

the image to the right. Paycareful attention to how theinitial forces that keep thecart in a state of static

equilibrium can be replacedby the tension in thestrings.

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Lesson 4-5d Everyday Forces

Static Equilibrium

The logic behind these problems is simple. If theobject experiences no acceleration, then the netforce is zero.

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Lesson 4-5d Everyday Forces

Static Equilibrium

We can use the weight of the object to find the y-components of the forces exerted along thestrings.

Click on the imageto the right.

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Lesson 4-5d Everyday Forces

Static Equilibrium

Example 1. The picture to theright shows a 5.00 kg mass

hanging from two strings.String 1 makes an angle of35.0o above the horizontal.String 2 makes an angle of

54.0o

above the horizontal.Find the tension in each string.

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Lesson 4-5d Everyday Forces

Static EquilibriumStep 1. Superimpose the

x-axis and y-axis onto

the picture.Step 2. Add the angles

that you have beengiven.

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Lesson 4-5d Everyday Forces

Static EquilibriumStep 1. Superimpose the

x-axis and y-axis onto

the picture.Step 2. Add the angles

that you have beengiven.

Step 3. Calculate theweight of the object,and add the weightvector to the diagram.

N49.1-)m/skg)(-9.81(5.00mgFw2!!!

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Static EquilibriumStep 4. Draw the x and y

components of the force

exerted by the strings.

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Static EquilibriumStep 4. Draw the x and y

components of the force

exerted by the strings.Step 5. Write equations

for the x and y axisseparately.

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Static Equilibriumx-axis

0NFFF 2x1xx !!72x1x F-F !

o

2

o

1 54.0cosF-35.0cosF !

21 0.5878F0.8192F !

21 0.7175FF !This tells us that string 2 is under more

tension, holding more of the weight than

string 1. Does that make sense?

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Static Equilibriumy-axis

0NFFFF w2y1yy !!7w2y1y F-FF !

N49.154.0sinF35.0sinF o2o

1 !

21 0.7175FFRecall, !

N49.1F0.8090F0.5736 21 !

N49.1F0.8090)F1750.5736(0.7 22 !

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Static Equilibriumy-axis

N49.1F0.8090)F1750.5736(0.7 22 !

N49.1F1.221 2 !

N40.2F2 ! 21 0.7175FFRecall, !

N28.80.7175FFso, 21 !!

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Lesson 4-5d Everyday Forces

Static EquilibriumThere are several

different variations

of these problems,but this representsone of the hardertypes.