Freefall | Physics for GCSE/IGCSE - Year 11 PDF Download

Acceleration of Free Fall

• Without air resistance, every object descends with identical acceleration.
• This phenomenon is termed as freefall acceleration, alternatively known as gravity's acceleration.
  

Galileo observed that in environments lacking air resistance, all objects (near the Earth's surface) descend with an acceleration approximately equal to 9.8 meters per second squared.

• For each second of descent, the object's velocity rises by 9.8 meters per second.
• The symbol "g" represents the gravitational field intensity and is utilized to compute an object's weight by its mass:
  weight = mass × gravitational field strength
  W = mg

Motion of Falling Objects

Falling Objects without Air Resistance

• Without air resistance, all objects falling within a consistent gravitational field experience the same acceleration, irrespective of their mass.
• As long as air resistance remains negligible, the velocity of a falling object will consistently accelerate, progressively increasing with time.

Falling Objects with Air Resistance

• When objects fall through fluids (liquids or gases) in a uniform gravitational field, they experience two main forces:
  • Weight: This force is due to gravity.
  • Friction: Such as air resistance.

• Skydiver's Experience
  • When a skydiver jumps from a plane, they encounter:
    • An acting force of weight (mass × acceleration of freefall) directed downward.
    • An acting force of air resistance (frictional forces always oppose the direction of motion) directed upward.
• Air Resistance Increase with Speed
  • This force grows with velocity, as illustrated in the accompanying image.

Understanding Terminal Velocity in Skydiving

When a skydiver jumps out of a plane, several forces come into play that determine their speed and motion. Let's break down the concept of terminal velocity step by step:

Initial Stage of Freefall

• Initially, the upwards air resistance is minimal since the skydiver is not falling rapidly.
• Due to this slow fall, there are unbalanced forces acting on the skydiver at the beginning.

Increase in Falling Speed

• As the skydiver accelerates and gains speed, the air resistance they experience also increases.
• This increasing air resistance eventually reaches a point where it balances out the downward weight force acting on the skydiver.

Attaining Terminal Velocity

• When the air resistance equals the weight of the skydiver, the forces acting on them are balanced.
• At this point, there is no longer any resultant force affecting the skydiver's motion.
• As a result, the skydiver's acceleration becomes zero, and they continue to move at a constant speed.
• This constant speed that the skydiver reaches is termed as their "terminal velocity."

Terminal Velocity in Skydiving

• When a skydiver deploys the parachute, the air resistance experienced by the skydiver increases.
• This increase is primarily due to the larger surface area created by the parachute opening.
• The upward force of air resistance acting on the skydiver also increases, leading to a decrease in the acceleration of the skydiver's fall.
• As a result, the skydiver starts decelerating.
• Eventually, a new equilibrium is established where the forces balance out, and the skydiver reaches a slower terminal velocity.

Factors Contributing to Terminal Velocity

• The increased surface area of the parachute.
• The upward force of air resistance counteracting the force of gravity.
• The concept of deceleration and reaching a new equilibrium point.