Tuesday, 19 February 2013

1.17 describe the forces acting on falling objects and explain why falling objects reach a terminal velocity

When first an object is falling it is accelerating- the force acting downward (gravity) is larger than the force acting upwards (air resistance.) But when air resistance and gravity become equal the object will have reached its maximum speed; its terminal velocity.


  1. terminal velocity: the maximum speed that be can obtained traveling in a free-fall. WHY? THE PHYSICS BEHIND IT? OKAY IT'S ACTUALLY NOT THAT HARD. JUST WRITE THIS AND I'M SURE YOUR WILL GET THE MARKS:
    "The drag forces( opposing the motion: air resistance) have reached an increase where they balance out completely the weight forces. As a result of the balanced forces, the resultant force is zero and thus no further acceleration can occur- having reached its making velocity. For acceleration to occur there must be unbalanced forces.. following the formula F=ma"

  2. The only thing I don't understand about this is that forces can be 'balanced' and yet the object can still be moving. If the forces are balanced, surely the object should be stationary? If the object is still falling, surely the weight is greater than the air resistance? What, exactly, is meant by the term 'balanced'? None of my teachers have ever explained this very well.

    1. An object is either stationary or moving with a constant velocity with no changes to its direction or speed when it's 'balanced'. You just have to know that.

    2. Balanced in this sense means that the downward force is exactly the same as the upwards force.
      You are right to think that if they are balanced then something should stop, but it is not the movement that stops; it is the rate of change of speed that stops.
      From what I can remember of physics this is because the object is already in motion- so its like the forces have just sorted their dispute and are leaving the object to do its thing (which is falling at its current speed).

      You are the first person I’ve found to think like this!! In every physics lesson, I’ve asked that question – it just doesn’t make sense. If the forces are balanced, the object is stationary. How is it moving forwards if the backwards force is equal? I love physics, but this one principle has never made sense to me. I understand it, but I don’t understand why. My teachers just mumble some stuff like “oh yeah constant speed blah blah” but it doesn’t make sense!!!
      I love physics, but it sure is confusing!

    4. WOW, throwback and a half. Two years since I was doing what you're doing, hope it all goes well!