# Physics P3 Falling Safely

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• Created by: A.P
• Created on: 20-01-13 16:18
• Falling Safely
• Falling Objects
• All objects fall with the samea cceleration due to gravity as long as the effect of air resistance is very small.
• The size of the air resistance force on a falling object depends on...
• ...it's cross-sectional area - the larger the area the greater the air resistance.
• ...it's speed - the faster it falls the greater the air resistance.
• The speed of a free-fall parachutist changes as he falls to Earth.
• In picture 1, the weight of the parachutist is greater than air resistance. He accelerates.
• In picture 2 the weight of the parachutist and air resistance are equal. The parachutist has reached terminal speed, because the forces acting on him are balanced.
• In picture 3, the air resistance is larger than the weight of the parachutist. He slows down and air resistance decreases.
• In picture 4, the air resistance and weight of the parachutist are the same. He reaches a new, slower terminal speed.
• Terminal Speed
• In picture 1 the parachutist accelerates, displacing more air molecules every second. The air resistance force increases. This reduces his acceleration. So, the higher the speed, the more air resistance.
• In picture 2, the parachutist's weight is equal to the air resistance; the forces on him are balanced. He travels at constant speed - terminal speed.
• In picture 3, when the parachute opens, the upward force increases suddenly as there is a much larger surface area, displacing more air molecules every second. So, the larger the area, the more air resistance. The parachutist decelerates, displacing fewer air molecules each second, so the air resistance force decreases.
• In picture 4, the parachutist reaches a new slower terminal speed when his weight is equal to the air resistance once more, so he lands safely.
• Drag racers and the Space Shuttle use parachutes to slow them down rapidly.
• Gravitational Field Strength - g
• The force on each kilogram of mass due to gravity, g = 10 N/kg approximately on Earth.
• g is also known as aacceleration due to gravity, g = 10m/s2 approximately.
• The gravitational field strength...
• ...is unaffected by atmospheric conditions...
• ...varies with position on the Earth's surface (9.78N/kg at the equator and 9.83 N/kg at the poles)...
• ...and varies with height above or depth below the Earth's surface.