Contact & Non-Contact Forces

• Contact & Non-Contact Forces:

  • A force is defined as:A push or a pull that acts on an object due to the interaction with another object
  • Forces can have an effect on bodies in several different ways:
  • They can change their speed
  • They can change their direction
  • They can change their shape
• • Some examples of these changes are:
  • An engine can increase the speed of a vehicle due to a force called thrust
  • A comet’s direction can be affected by gravitational attraction
  • A spring can have its shape changed by the force from a heavy load
• Diagram showing the effects of forces on different objects:

  
• Important forces to be familiar with:

  • Weight – the name given to the force of gravity on a mass
  • Electrostatic force – the force between two charged objects
  • Thrust – the force causing an object to move (such as the force from a rocket engine)
  • Air resistance (or drag) – the friction of the air on a moving object
• Important forces to be familiar with:

  • Upthrust – the force of a fluid (such as water) pushing an object upwards (making it float)
  • Compression – forces that act inward on an object, squeezing it
  • Tension – force transmitted through a cable or a string when pulled on by forces acting on its opposite ends
  • Reaction force (or the normal force)– a force due to contact between two objects
• Diagram showing several different types of forces acting on objects (part 1):

  
• Diagram showing several different types of forces acting on objects (part 2):

  
• • All forces can be categorised into one of two types:
  • Contact forces
  • Non-contact forces
• Contact Forces

  • A contact force is defined as:A force which acts between objects that are physically touching
• • Examples of contact forces include:
  • Friction
  • Air resistance
  • Tension
  • Reaction force / Normal force
• Friction:

  • Is a force that opposes motion
  • Occurs when objects rub against each
  • Air resistance:
  • Is a type of friction
  • Occurs when an object moves through air
• Tension:

  • Is a force that pulls two objects connected by a length, such as a string or rope
  • Occurs when a force is applied to the length
  • Reaction force / Normal force:
  • Is a force that pushes touching objects apart
  • Occurs when objects are supported by a surface
• Examples of contact forces:

  
• Examples of contact forces:

  
• Non-Contact Forces:

  • A non-contact force is defined as:A force which acts at a distance, without any contact between bodies, due to the action of a field
  • Examples of non-contact forces include:
  • Gravitational force
  • Electrostatic force
  • Magnetic force
• • Gravitational attraction:
  • The attractive force experienced by two objects with mass
  • For example, the force between a planet and a comet
• • Electrostatic force:
  • A force experienced by charged objects which can be attractive or repulsive
  • For example, the attraction between a proton and an electron
• • Magnetic force:
  • A force experienced between magnetic poles that can be attractive or repulsive
  • For example, the attraction between the North and South poles of magnets
• Examples of non-contact forces: