Subjects
Grades
Material Forces and Constraints
Concept sheet | Science and Technology
Secondary
1-4
Table of contents
Forces
A force is an action which can set a body in motion, modify its motion, or deform it.
Modifying the resting state of a body means setting it in motion.
To launch a paper plane in the air, a force must be applied to it.
Applying force to the paper plane to set it in motion
MH-Lee, Shutterstock.com
Modifying the motion of a body means slowing it down, accelerating it, or modifying its trajectory.
To change the speed and trajectory of a puck, you have to act on it by applying a force with the stick.
Applying force to the puck to modify its trajectory
Steve Gilbert, Shutterstock.com
To deform an object means to modify its shape.
A ball of dough is crushed by applying a force of compression.
Compression force applied on a ball of dough
Johnny Bravoo, Shutterstock.com
Constraints
If several forces are exerted simultaneously on a material, it can tend to deform in different ways. The effect of these forces on the material is called a constraint.
Constraints
Moments in the video:
- 00:00-Introduction
- 00:53-Compression
- 01:41-Tension
- 02:34-Torsion
- 03:32-Deflection
- 04:27-Shearing
- 05:19-Conclusion
There are different constraints depending on the number and orientation of the forces exerted.
Compression
|
Application of forces |
Symbol |
|---|---|
|
Two forces applied towards each other |
 |
|
Effect |
|
|
Tendency to crush materials |
Compression constraint on a mountain bike suspension
DaniiD, Shutterstock.com
Tension
|
Application of forces |
Symbol |
|---|---|
|
Two forces applied in opposite directions |
 |
|
Effect |
|
|
Tendency to stretch materials |
Tension constraint on a climbing rope
Dmytro Balkhovitin, Shutterstock.com
Torsion
|
Application of forces |
Symbol |
|---|---|
|
One or two parallel forces in opposite directions applied to an object so that it rotates around an axis |
 |
|
Effect |
|
|
Tendency to twist materials |
Torsion constraint on a dishcloth
Lek in a BIG WORLD, Shutterstock.com
Bending
|
Application of forces |
Symbol |
|---|---|
|
One or more parallel forces in opposite directions, applied at different places on an object |
 |
|
Effect |
|
|
Tendency to fold or bend materials |
Bending constraint on a slackline
Vaclav P3k, Shutterstock.com
Shearing
|
Application of forces |
Symbol |
|---|---|
|
Two parallel and opposing forces applied slightly apart from each other |
 |
|
Effect |
|
|
Tendency to tear or split materials |
Shearing constraint on a sheet of paper
Einar Muoni, Shutterstock.com
Effects of Constraints
The Effects of Constraints
Moments in the video:
- 00:00-Introduction
- 00:19-Elastic deformation
- 00:47-Permanent deformations
- 01:16-Fracture
Depending on the nature of the material and on the magnitude of the force applied, the deformation may be invisible or apparent.
If a tension constraint is applied to a non-elastic rope, the rope retains its shape and does not stretch. The deformation is not apparent.
Rope that does not deform
Marc Dietrich, Shutterstock.com
If a tension constraint is applied to a rubber band, it deforms while stretching. The deformation is apparent.
Apparent deformation on a rubber band
Sharomka, Shutterstock.com
Constraints can cause two types of deformation, temporary deformation and permanent deformation.
|
Type of deformation |
Description |
Example |
|---|---|---|
|
Temporary (or elastic) deformation |
The material is deformed when the constraint is applied; it then returns to its original shape when the constraint ceases to be applied. |
A trampoline that deforms when subjected to the weight of a person  Pavel1964, Shutterstock.com |
|
Permanent (or plastic) deformation |
The material deforms when the constraint is applied, but does not recover its original shape when the constraint ceases to be applied. It retains its new form. |
Plasticine that deforms when crushed  DanitzaPulgarM, Shutterstock.com |
Materials have a strength threshold, that is, a maximum force that they can withstand. If the constraint exceeds the strength threshold of the material, the material breaks. This effect is called a fracture.
When inflating a balloon, the rubber undergoes a tension constraint and deforms. If the constraint exceeds the strength threshold of the material, the balloon bursts. This is what is known as a fracture.
Deformation of a rubber balloon
5 second Studio, Shutterstock.com
Fracture of a rubber balloon