Resultant forces

• What is the resultant force?

  One force acting in a single direction
• What do free body diagrams show?

  • All forces acting on an object
  • Excludes forces exerted on the environment
• What forces act on a skydiver?

  Weight and drag (air resistance)
• How are the sizes of arrows in free body diagrams interpreted?

  • Arrow size indicates force magnitude
  • Arrow direction indicates force direction
• What must be true for forces to be replaced by a resultant force?

  They must have the same overall effect
• How do you find the overall effect of parallel forces?

  Add forces in the same direction, subtract others
• What is the resultant force if horizontal forces are 1200 N and 1000 N?

  200 N to the left
• What happens when a resultant force moves an object?

  Work is done and energy is transferred
• What is the relationship between work done and energy transferred?

  They are the same concept
• How is work done calculated?

  Work done (J) = Force (N) × Distance (m)
• What is one joule of work equivalent to?

  One newton metre (Nm)
• How do you use scale drawings to find resultant forces?

  1. Draw forces to scale, tip to tail
  2. Draw a straight line from start to end
  3. Measure length for magnitude and angle for direction
• What is the driving force of the electric bicycle in the example?

  4 N north
• What is the wind force acting on the bicycle?

  3 N east
• How do you find the resultant force from the bicycle example?

  Use scale drawing to measure resultant
• What is the resultant force magnitude in the bicycle example?

  5 N
• What is the direction of the resultant force in the bicycle example?

  On a bearing of 037°
• What happens when you push something along a rough surface?

  • Work is done against friction
  • Energy is transferred to kinetic and thermal stores
  • Temperature of the object increases
• What is the formula for work done?

  W = Fs
• What is the scale used in the bicycle example?

  1 cm = 1 N
• What is the length of the resultant force in the bicycle example?

  5 cm
• What angle is measured for the resultant force in the bicycle example?

  37°