Frictional Force and Stopping Distance

Friction is always there to slow things down
1. If an object has no force propelling it along it will always slow down and stop because of friction
  1. Friction always acts in the opposite direction to movement
  2. You get friction between two surfaces in contact or when an object passes through a fluid (drag)
2. To travel at steady speed the driving force needs to balance the frictional forces
3. Resistance or drag from fluid (air or liquid)
  1. Most of the resistive forces are caused by air resistance or drag. The most important factor by far in reducing drag in fluids is keeping the shape of the object streamlined. The opposite extreme is a parachute which is about as high drag as you can get
  2. Drag increases as the speed increases
    1. Frictional forces from fluids always increases with speed. A car has much more friction to work against when travelling. So at 70 mph the engine has to work much harder just to maintain a steady speed
Objects falling through fluids reach a terminal velocity
1. When falling objects first set off the force of gravity is much more than the frictional force slowing them down so they accelerate. As the speed increases the friction builds up. This gradually reduces the acceleration until eventually the frictional force is equal to the accelerating force and then it wont accelerate any more. It will have reached its maximum speed or terminal velocity and will fall at a steady speed
The teminal velocity of falling objects depend on there shape and area
1. The accelerating force acting on all falling objects is gravity and it would make them all fall at the same rate. However on earth air resistance causes things to fall at different speeds and the terminal velocity of any object is determined by its drag in comparison to its weight. The frictional force depends on its shape and area
2. W=mg
Stopping distances
1. Many factors affect your total stopping distance
  1. The faster a vehicle is going the bigger braking force itll need
  2. The faster your going the greater your stopping distance-if your maximum braking force isnt enough youll go further before you stop
  3. The total stopping distance of a vehicle is the distance covered in the time between the driver first spotting a hazard and the vehicle coming to a complete stop
  4. The stopping distance is the sum of the thinking distance and the braking distance
2. Thinking distance
  1. affected by two main factors
    1. How fast your going
    2. How dopey you are e.g. tiredness etc
  2. Bad visibility and distractions can also be a major factor in accidents e.g. radio may mean that a driver doesnt notice a hazard until they are quite close
3. Braking distance
  1. Its affected by four main factors
    1. How fast your going
    2. How good your brakes are
    3. How good the tyres are
    4. How good the grip is
  2. Wet or icy roads are always much more slippy than dry roads so you wont have much grip so you travel further before stopping

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Frictional Force and Stopping Distance

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