Interactions of Forces

• Scalar quantities have magnitude only
• Vector quantities have magnitude and an associated direction
• A vector quantity may be represented by an arrow

  • The length of the arrow represents the magnitude
  • The direction of the arrow the direction of the vector quantity
• A force is a push or pull that acts on an object due to the interaction with another object
• Contact forces – the objects are physically touching
• Contact forces – the objects are physically touching
• Contact forces

  • Friction
  • Air resistance
  • Tension
  • Normal contact force
• Non-contact forces

  • Gravitational force
  • Electrostatic force
  • Magnetic force
• Force is a vector quantity
• Weight is the force acting on an object due to gravity
• The force of gravity close to the Earth is due to the gravitational field around the Earth
• The weight of an object depends on the gravitational field strength at the point where the object is
• $W =$$mg$

  • Weight (W) in newtons (N)
  • Mass (m) in kilograms (Kg)
  • Gravitational field strength (g) in newtons per kilogram (N/Kg)
• The weight of an object may be considered to act at a single point referred to as the object’s centre of mass
• The weight of an object and the mass of an object are directly proportional
• Weight is measured using a calibrated spring-balance (a newtonmeter)
• A resultant force is a single force that has the same effect as all the original forces acting together
• A single force can be resolved into two components acting at right angles to each other