Shear modulus facts for kids

The shear modulus is a way to measure how stiff a solid material is when it is twisted or pushed sideways. Imagine you have a block of jelly. If you push the top of the jelly sideways while holding the bottom still, it changes shape. The shear modulus tells you how much force you need to do this.

It is often called the modulus of rigidity. Scientists usually use the letter G to stand for shear modulus. It helps us understand how materials behave under certain types of stress.

What is Shear Modulus?

The shear modulus measures a material's resistance to a shearing force. A shearing force is one that pushes parts of an object in opposite directions. Think of cutting paper with scissors. The blades create a shearing force.

When an object is sheared, its shape changes, but its volume stays mostly the same. The shear modulus tells us how much the material will deform. A high shear modulus means the material is very stiff. It will not deform much under a shearing force.

How Does it Work?

Imagine a rectangular block of rubber. If you glue the bottom of the rubber block to a table, then push the top surface sideways, the block will lean over. It changes its shape from a rectangle to a parallelogram.

The shear modulus (G) is found by dividing the shear stress by the shear strain.

• Shear stress is the force applied per unit area. It is how much pushing force is spread over a certain surface.
• Shear strain is how much the material deforms. It is measured by the angle of deformation.

So, if you apply a certain amount of force, a material with a high shear modulus will deform less. A material with a low shear modulus will deform more.

Units of Measurement

The shear modulus is measured in units of pressure. The standard unit is the pascal (Pa). One pascal is equal to one newton per square metre (N/m²).

Sometimes, you might see it measured in gigapascals (GPa). One gigapascal is one billion pascals. This unit is used for very stiff materials like metals.

Why is Shear Modulus Important?

Understanding shear modulus is very important in engineering and design. It helps engineers choose the right materials for different jobs.

• Building bridges and structures: Engineers need to know how much a material will twist or bend under different forces. This prevents buildings from collapsing.
• Designing machine parts: Parts like axles, shafts, and gears often experience twisting forces. The shear modulus helps ensure these parts are strong enough.
• Making tools: Tools like wrenches or screwdrivers need to resist twisting without breaking. Their materials are chosen based on their shear modulus.
• Sports equipment: Materials in things like skis or tennis rackets need specific stiffness properties. This affects how they perform.

For example, rubber has a low shear modulus, so it is easy to twist and stretch. Steel has a very high shear modulus, making it hard to deform.

Shear Modulus in Everyday Life

You can see the effects of shear modulus all around you:

• When you twist a wet towel, you are applying a shearing force. The towel's fibers resist this twist.
• When you walk, your shoes grip the ground. This grip involves shear forces between your shoe and the surface.
• The springs in a car's suspension system work by twisting and compressing. The material of the springs needs a specific shear modulus.

Different materials have different shear modulus values. This is why some things are easy to bend or twist, while others are very rigid.

Images for kids

• 

  Influences of selected glass component additions on the shear modulus of a specific base glass.

See also

• 
• Shear modulus for kids in Spanish