IGCSE Physics - 1.5.1 Effects of Forces

Objective: Know that forces may produce changes in the size and shape of an object

Introduction

Forces can cause changes in the size and shape of objects. These changes can be permanent or temporary, depending on the type of force and the material of the object.

Types of Forces and Their Effects

1. Pressure

Pressure is defined as the force acting perpendicular to a surface per unit area. It can cause an object to become compressed or deformed.

• External Pressure: Forces applied from outside an object. Examples include the pressure of air, water, or a solid object pressing against something.
• Internal Pressure: Forces exerted by the molecules within an object. Examples include the pressure in a gas or liquid.

2. Tension

Tension is the pulling force transmitted along a string, rope, cable, or similar object when it is pulled tight by forces acting from opposite ends.

Tension can cause an object to be stretched or deformed.

3. Compression

Compression is a force that pushes or squeezes an object together, reducing its size.

Compression can cause an object to be deformed, especially if the material is weak.

4. Shear

Shear is a force that acts parallel to a surface, causing layers of the material to slide past each other.

Shear forces can cause objects to deform or break, particularly in materials that are weak in shear.

5. Bending

Bending is a type of shear force that causes an object to curve.

Bending can be used to create structures that are strong and flexible.

Examples of Forces Causing Changes in Size and Shape

Force	Description of Effect	Example
Pressure (Water)	Compresses a balloon	Submerging a balloon in water increases its internal pressure, causing it to shrink.
Tension (Rope)	Stretches a rope	Pulling on a rope increases its length.
Compression (Weight on a Spring)	Shortens a spring	Putting weight on a spring causes it to compress.
Shear (Cutting Paper)	Causes paper to tear	Applying a force sideways to a piece of paper causes it to shear and tear.
Bending (Walking on a Beam)	Causes a beam to bend	When a person walks on a beam, the weight causes it to bend.

Factors Affecting Deformation

The extent to which a force changes the size and shape of an object depends on several factors:

• Material Properties: The material's stiffness (Young's modulus) determines how much it will deform under a given force. Stiffer materials deform less.
• Area: The larger the area over which the force is applied, the less pressure is exerted.
• Strength of the Material: The material's ability to withstand deformation before breaking.

Conclusion

Forces can cause significant changes in the size and shape of objects. Understanding the different types of forces and their effects is crucial in many areas of physics and engineering.