Page 62 -

Unit summary

Check your knowledge and understanding

1. Using your knowledge of the structure of matter, explain how elastic forces occur. What does
elastic force depend on?
2. Imagine you are bungee jumping. Describe what happens to the elastic cord during a jump,
textbooks nis edu kz
using the key words from this unit. Draw a picture to help you explain.

3. Think of two examples of each kind of elastic and plastic deformations of objects. Complete
the table.

bending torsion shear extension compression

4. Which objects in your home experience deformations? Explain your answer.

5. A student doing laboratory work measures the coefficient of a spring and obtains the
following data:

F /N 100 200 300 400 500
el
Δl /m 0.05 0.1 0.15 0.2 0.25

a) Using the data in the table, plot an elastic force vs. spring deformation graph.

b) Use the graph to calculate the coefficient of the spring.

c) How will the graph change if the spring’s coefficient is:

i) doubled? ii) halved?

Assess your learning

Reflect on how well you met the learning objectives of this unit. Use the worksheet provided by
your teachers to develop your own targets.

How confident am I?

I can …
explain the difference between plastic and elastic deformation, using key words

name and explain at least 5 kinds of deformation
measure elastic force using a dynamometer

apply Hooke’s Law to calculate the elastic force, coefficient and elongation (compression) of a spring
plot elastic force vs. deformation length from extension in the case of stretching

calculate the coefficient of a spring using a graph
explain when Hooke’s Law is applicable
use correct scientific terminology in sentences, for example, depends on, under the effect of, measured in,
occurs when, has a larger angle of slope, etc.

62