Contact Forces (HL IB Physics)

• 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, F_f

• 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

Fluid resistance or viscous drag, F_d

• 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, F_T

• 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 / reaction force, F_N

• Reaction forces occur 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