• Falling objects experience?two forces:
  • Weight?(due to gravity)
  • Air resistance?(due to friction)

   

• The force of air resistance increases with speed. This is illustrated in the image below:

Debbie initially accelerates downwards due to her weight. The upwards air resistance increases as she falls until it eventually grows big enough to balance the weight force

• Initially, the upwards air resistance is?very small?because the skydiver isn't falling very quickly
  • Therefore, there are?unbalanced?forces on the skydiver initially

   

• As the skydiver speeds up, air resistance?increases,?eventually growing large enough to?balance the downwards weight force
• Once?air resistance equals weight,?the forces are?balanced
  • This means there is no longer any?resultant force

   

• Therefore, the skydiver's acceleration is?zero?- they now travel at a?constant?speed
• This speed is called their?terminal velocity

Part (a)

The weight of an object is the force of?gravity?which acts on it.

• • The weight force is due to the Earth's gravitational pull on the object, so weight is due to gravity

   

Part (b)

When something falls, initially it?accelerates.

• • The?resultant force?on the object is?very large?initially, so it accelerates
  • This is because there is a?large unbalanced force?downwards (its weight) - the upward force of air resistance is very small to begin with

   

Part (c)

The faster it falls, the larger the force of?friction?which acts on it.

• • The force of?air resistance?is due to?friction?between the object's motion and?collisions with air particles
  • Air particles try to slow the object down, so air itself produces a?frictional force, called air resistance (sometimes called?drag)

   

Part (d)

Eventually it?falls at a steady speed?when the force of friction equals the force of gravity acting on it.

• • When the upwards?air resistance?grows enough to?balance?the downwards?weight?force, the resultant force on the object is?zero
  • This means the object isn't accelerating - rather, it is moving at a?steady?(terminal)?speed

   

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