Newton's First and Second Laws

• Force


  Needed to change motion
• Newton's First Law


  • A resultant force is needed to make something start moving, speed up or slow down
  • If the resultant force on a stationary object is zero, the object will remain stationary
  • If the resultant force on a moving object is zero, it'll just carry on moving at the same velocity
• Constant velocity


  1. Resistive and driving forces are balanced

  2. Velocity will only change if there's a non-zero resultant force acting on the object
• Acceleration


  • A non-zero resultant force will always produce acceleration (or deceleration) in the direction of the force
  • Acceleration can take five different forms: starting, stopping, speeding up, slowing down and changing direction
  • On a free body diagram, the arrows will be unequal
• Acceleration


  • Proportional to the resultant force
  • Inversely proportional to the mass of the object
• Large forces are needed to produce large accelerations