P8 newton's laws of motion

• newton's 1st law of motion:

  objects either stay at rest or move with constant velocity unless acted on by a force
• newton's first law of motion means that an object moving at constant velocity is either acted on by no forces, or the forces acting on it are balanced
• weight is not the same as mass, the equation that links weight and mass is W=mg

  W = weight

  m = mass

  g = gravitational field strength
• when an object is in equilibrium, the support force is equal and opposite to the weight
• weight is different in different locations, depending on the gravitational field strength, but mass is always the same
• mass is a measure of the inertia of an object
• inertia is the resistance to change of motion
• newton's 2nd law of motion:

  the acceleration of an object is proportional to the resultant force experienced by the object
• the equation for newton's second law is F=ma

  F = force in $N$

  m = mass in $kg$

  a = acceleration in $ms^{-2}$
• any object moving through a fluid experiences a drag force

  the size of the drag force depends on the shape of the object, speed of the object, and viscosity of the fluid
• as an object falls through a fluid, its speed increases, so the drag force increases

  as the drag force increases, the resultant force decreases, so the acceleration decreases

  eventually, the object reaches terminal speed, which is when the drag force is equal and opposite to the weight of the object, so the acceleration is zero and speed is constant
• thinking distance = the distance travelled by a vehicle in the time it takes for the driver to react
• braking distance = the distance travelled by a vehicle in the time it takes to stop, once the brakes have been applied
• stopping distance = thinking distance + braking distance
• impact force is the force generated by a collision
• impact time is the time over which the impact force occurs
• vehicle safety features are designed to increase the impact time, therefore reducing the impact force, to protect the passengers in the vehicle
• common vehicle safety features:

  • seat belts
  • airbags
  • collapsible steering wheels
  • crumple zones
  • bumpers