Drag and Terminal Velocity

Friction slows things down

• If an object has no force applied to it then 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 equal/balance the frictional force
• You get friction between two surfaces in contact or through a fluid
• Less friction if an object is more streamlined e.g. fish
• More friction if the object is less streamlined e.g. parachute

Drag (friction) increases as speed increases

When cars and free-falling objects set of they have a higher acceleration force compared to the resistance. As acceleration increases so does resistance. This gradually reduces the acceleration until it equals the resistance. When this happens the object has reached its max speed, in other words: terminal velocity !

The accelerating force acting on free-falling objects is gravity and this would make all objects fall at the same rate if it wasn't for air resistance. This means on the moon hamsters and feathers will hit the ground simultaneously but on Earth the terminal velocity of an object depends on the drag in comparison to weight which in turn depends on the shape and area of an object.

An example of what I described above is a skydiver with the parachute closed and open the air resistance is very different.