Terminal Velocity

• If an object has no force propelling it along it will always slow down and stop because of friction.

  Friction always acts in the opposite direction to movement
• To travel at a steady speed, the driving force needs to balance the frictional forces.

  You get friction between two surfaces in contact or when an object passes through a fluid (drag).
• Drag is the resistance you get in a fluid eg air resistance
• The most important factor in reducing drag is keeping the shape of the object streamlined. This is where the object is designed to allow fluid to flow easily across it, reducing drag. Parachutes work in the opposite way- they want as much drag as they can get.
• Frictional forces from fluids always increase with speed. A car has much more friction to work against when travelling at 70mph compared to 30mph. So at 70mph, the engine has to work much harder to maintain a steady speed
• When a falling object first sets off, the force of gravity is much more than the frictional force slowing it down so it accelerates. As the speed increases the friction builds up. This gradually reduces the acceleration until eventually the frictional force is equal to the accelerating force (so the resultant force is zero). It will have reached its maximum speed or terminal velocity and will fall at a steady speed
• The accelerating force acting on all falling objects is gravity and it would make them all fall at the same rate if it wasn’t for air resistance. But 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.
• The most important example is the human skydiver.