Contact Forces (DP IB Physics: SL): Revision Note

Contact Forces

• A contact force is defined as:

A force which acts between objects that are physically touching

• Examples of contact forces include:

  • friction

  • fluid resistance or viscous drag

  • tension

  • normal (reaction) force

Surface friction

• Surface friction is a force that opposes motion

• Occurs when the surfaces of objects rub against each other, e.g. car wheels on the ground

Viscous drag

• Fluid resistance, or viscous drag , is a type of friction

• Occurs when an object moves through a fluid (a liquid or a gas)

• Air resistance is a type of fluid resistance or viscous drag force

Tension force

• Tension is a force that occurs within an object when a pulling force is applied to both ends 

• Occurs when two forces are applied in opposite directions to the ends of an object e.g. a mass on a spring suspended from a clamp

Normal force

• The normal force occurs when an object is supported by a surface

• It is the component of the contact force acting perpendicular to the surface that counteracts the body e.g. a book on a table

Examples of contact forces