3.3 Hooke’s Law

TODAY’s OBJECTIVES• To learn about how stretch or compression of a spring varies

with gravitational force.

Words to Know for 3.3Hooke’s Law

Spring Constant, k

Predict What Happen…

1. Take three different known masses and a rubber band

2. Measure the length of the rubber band as it hangs from a hook

3. Hang the smallest mass and measure the distance the rubber band stretches.4. Predict how far the rubber band will

stretch with mass #2 and mass #35. Test each one and record your

predictions into your notebook

Predict What Happen…

How do you think the “stretchiness” of a

spring varies with the weight of an object

causing that stretchiness?

Spring Constant

1. Linear graph2. Direct proportion

x = amount of stretching/compression

F = force exerted on an object (Fg

, Fapp…)

1. Linear graph2. Direct proportion

x = amount of stretching/compression

F = force exerted on an object (Fg

, Fapp…)

How can you write a formula which expresses this

relationship?

Spring Constant

x = amount of stretching/compression

F = force exerted on an object (Fg

, Fapp…)

F ∝ x

Spring Constant

F = k · x

k = spring constant

F = k · ∆x

Robert Hooke

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• First one to notice this relationship

Robert Hooke

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• If too much force is applied and an object is stretched or compressed too much, the direct proportion breaks down!

Example 1

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Fapp = ??

∆x = 20 cm = 0.20 mk = 3.2

Fapp = k · ∆x

Fapp = 3.2 · 0.20

Fapp = 0.64 N

1.33 N/cm

Example 1

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m = 2.5 kg∆x = 10 cm = 0.10 mIf,m = 5.0 kg∆x = ???

Fg = k · ∆x

m · g = k · ∆x

2.5 · 9.8 = k · 0.10k = 245 N/m

Fg = 245 · ∆x

CLASSWORKProblems: 3.3 Review Problems

Page: 97

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HOMEWORKProblems: Chapter 3 Review Questions (# 10)

Page: 99

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Chapter 3 TEST

Thursday, November 14

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Chapter 3 TESTProblems: Chapter 3 Review Questions (# 1 - 9)

Page: 98 - 99

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LaboratoryInvestigation 3 – 3

Another Way to Weigh

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