Presentation on theme: "Motion of mass on a parachute Falling objects increase their speed as they fall. This is due to their weight (the force of gravity) that pulls them."— Presentation transcript:
Motion of mass on a parachute Falling objects increase their speed as they fall. This is due to their weight (the force of gravity) that pulls them to the earth They also experience an upward force called air resistance (drag), which slows them down. Graph showing the motion of a skydiver
Terminal Velocity When an object falls, it will accelerate towards the Earth, due to the force of gravity acting on it. This force can also be called weight. Frictional forces between the air and the object will act in the opposite direction. The faster the object falls, the more air it passes through, so air resistance, or drag, gradually increases. If the falling object has a large surface area, the force of friction will be greater. A parachute provides a large surface area. When the force of friction acting upwards equals the force of gravity acting downwards on the object, the resultant force will be zero. The object then falls at a steady speed. This speed is called the terminal velocity. When a vehicle has a steady speed, the driving force of the engine is equal to the frictional forces due to the air and the road.
Stokes Law F = 6 πηr v F is the drag force from the parachute r is the radius of the parachute v is the velocity at which the parachute falls η is the viscosity of the air r F v
Stokes Law If the parachute is falling at a steady speed (terminal velocity) Weight of payload = 6 πηr v T Weigh = mg mg = 6 πηr v T Rearranging v T = mg/6 πηr v T should be proportional to m. vTvT 6 πηr v T mg