3 3 Hookes Law TODAYs OBJECTIVES To learn

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. 3 Hooke’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 #3 5. 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 graph 2. Direct proportion x = amount of stretching/compression F = force exerted on an object (Fg ,

Spring Constant 1. Linear graph 2. Direct proportion How can you write a formula which expresses this relationship? x = amount of stretching/compression F = force exerted on an object (Fg ,

Spring Constant F=k· ∆x k = spring F∝x constant F=k·x x = amount of stretching/compression F = force exerted on an object (Fg ,

Robert Hooke • First one to notice this relationship 9

Robert Hooke • If too much force is applied an object is stretched or compressed too much, the direct proportion breaks down! 10

Example 1 Fapp = ? ? ∆x = 20 cm = 0. 20 m k = 3. 2 Fapp = k · ∆x Fapp = 3. 2 · 0. 20 Fapp = 0. 64 N 1. 33 N/cm 11

Example 1 m = 2. 5 kg ∆x = 10 cm = 0. 10 m If, m = 5. 0 kg ∆x = ? ? ? Fg = k · ∆x m · g = k · ∆x 2. 5 · 9. 8 = k · 0. 10 k = 245 N/m Fg = 245 · 12

CLASSWORK Problems: 3. 3 Review Problems Page: 97 13

HOMEWORK Problems: Chapter 3 Review Questions (# 10) Page: 99 14

Chapter 3 TEST Thursday, November 14 15

Chapter 3 Problems: TEST Chapter 3 Review Questions (# 1 - 9) Page: 98 - 99 16

Laboratory Investigation 3 – 3 Another Way to Weigh 17