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Physics

EXT What else is Robert Hooke famous for? Prepare small leaflets for
your classmates about Robert Hooke and his scientific achievements.

Elastic force = coefficient of the spring × deformation 0 0 0
f = 0
1 1 1
F el = Δ
2 2 W 2
F el – elastic force, N (Newton) f = w
3 3 3 W
textbooks nis edu kz
k – coefficient of the spring (hardness of the object), N/m (Newton 4 4 4 W
per metre) scale showing f = 2 w
elongation
Δl – deformation (elongation) (change of object’s length during
deformation), m (metre)
elastic force, N
(The hardness of the object depends on the material, and on its shape
and size.) 20
10
REMEMBER! Elastic force occurs during deformation of objects due to
changes in the position of particles.
deformation, m
Elastic force is directed the opposite way to the external force that
causes the deformation.
support
If the force that is causing the deformation stops acting, the object
returns to its initial condition or remains deformed. spring

Hooke’s Law: the magnitude of elastic force during elastic extension (or
0
compression) is directly proportional to the change in body length. 5 pointer
10
Hooke’s Law works during small elastic deformations. scale 15
20 pan
INV Determine the magnitude of deformation of a dynamometer 25
30 weight
spring if a force of 10 N acts on it and its coefficient of spring is 500 N/m.
Plot an elastic force vs. spring deformation graph.

table
given SI solution
F = 10 N N F el = F Hooke’s Law – force proportional
k = 500 N/m N/m F el = kΔl to stretch
Δl = ? m Δl = F el /k
Δl = 10 N/500 N/m = 0.02 m
Answer: Δl = 0.02 m

OVER TO YOU!

1. A chandelier suspended in a hall is 3. Bungee jumping is an extreme sport practised all over
attracted by the Earth. Why does it the world. Look at the images on the previous page and
not fall? answer the following questions:

2. Calculate whether a fisherman can take a) What material is the cord made of? What properties
300 g of fish out of the water using a should it have?
fishing rod. The coefficient of elasticity of
b) Describe how a jumping man changes his position
the fishing line is 400 N/m, and it can be
during the free fall after jumping off the bridge.
stretched 10 mm with no disruption.
c) Suggest your ideas to perform the most efficient jump.
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