Resultant forces

• Resultant force


  A single force that has the same effect as all of the original forces acting together
• Calculating resultant force


  Subtract the smaller force from the larger force
• Calculating resultant force


  • Example 1: Man pushing box, force of 20N right, friction force of 10N left, resultant force of 10N right
  • Example 2: Car, driving force of 10,000N left, friction force of 4,000N right, air resistance of 5,000N right, resultant force of 1,000N left
• When forces are balanced, the resultant force is zero
• Free-body diagram


  • Shows the object as a point, forces drawn as arrows starting from the point, length of arrow shows size of force, direction of arrow shows direction of force
• Free-body diagrams


  • Example 1: Skydiver, weight force of 800N down, air resistance force of 800N up, resultant force is zero
  • Example 2: Aeroplane, weight force down, lift force up, thrust force forward, drag force backward, resultant forces balanced