Motion

• Friction is the force that opposes a relative motion for bodies that are in contact
• Air resistance is an opposing force due to a body rubbing against air molecules as it moves through air.
• A body falls due to it's weight.
• When a body falls in the absence of air resistance it falls with a constant acceleration due to gravity hence g = 9.8m/s2.
• When a body falls in the presence of air resistance the forces in volved are weight and air resistance.
• Weight is always constant but air resistance changes.
• Air resistance is directly proportional to the speed of the body.
• Resultant force decreases when the air resistance increases as weight is larger and the air resistance slowly increases when it is less. Resultant becomes smaller hence, acceleration decrease.
• Terminal velocity is reached when resultant force is zero.
• A parachute reduces the rate at which an object falls by increasing its air resistance.
• The speed of an object falling slowly increases but decreases due to air resistance.
• Air resistance gradually increases resulting in a decrease in resultant force hence a decrease in acceleration.
• When air resistance is equal to weight, the body falls with terminal velocity
• • A-B: The graph is almost straight therefor there is constant acceleration. At the start are resistance is negligible and weight is constant
  • B-C: Acceleration is decreasing. Air resistance is gradually increasing due to an increase in the speed, and since weight is constant the resultant force decreases.
  • C-D: The body travels at terminal velocity and its acceleration is 0. Weight and air resistance are equal, hence the resultant force is 0/none.

  
• • Body Falling when a parachute is opened:
  • A-B: Constant acceleration. Air resistance is negligible and weight is constant. The body is in freefall, the body is increasing speed.
  • B-C: Decreasing acceleration. Air resistance is increasing as the weight remains constant. This reduces resultant force.
  • C-D: The body is at terminal velocity and the acceleration is 0. Weight and air resistance are equal, the resultant force is 0.
  • D-E: Constant deceleration. The parachute is opened, air resistance increases due to the larger surface area. Air resistance becomes larger than weight.

  
• What Happends after E?

  Terminal velocity is reached. Weight and air resistance are equal.