Falling Objects and Gravity

Force on Falling Objects

• Aristotle believed that the speed of falling objects depends on their weight, but his idea was unclear.
• Galileo Galilei proved that objects of the same size and shape, but with different masses, fall at the same time towards the Earth when dropped from the same height, disproving Aristotle's idea.
• Isaac Newton demonstrated and explained why objects fall towards the Earth, citing two forces: the weight of the object and air resistance.

Experiment on Force on Falling Objects

• In an experiment, a coin and a feather of roughly the same surface area were made to fall in a plastic tube.
• With air in the tube, the feather fell much more slowly than the coin.
• After pumping out the air, the feather fell much more rapidly, almost as fast as the coin.

Key Points

• All bodies fall towards the Earth at a speed of 9.8 m/s², regardless of their size and mass.
• Acceleration due to gravity (g) is 9.8 m/s².

Characteristics of Free Falling Objects

• Free falling objects do not encounter air resistance and accelerate downwards at a rate of 9.8 m/s².
• Free fall occurs when an object falls under the sole influence of gravity.

Drag Force

• As an object falls through the air, it experiences an upward force called air resistance or drag force.
• Drag force depends on the speed of the falling body, area of the body, density of the air, and drag coefficient.
• Drag Force = 0.5 x d x v² x A x C

Terminal Velocity

• Terminal velocity is the constant maximum velocity reached by a body falling through the atmosphere under gravity.
• It occurs when the sum of the drag force and buoyancy equals the downward force of gravity acting on the object.

Work and Power

• Work is any action or activity where force is applied, such as a weightlifter exerting force to hold a heavy load or a student solving physics problems.
• Work is done only when a body is displaced under the application of force along the direction of force.

Work Done

• Work done = Force x displacement x cosθ (W = Fxd x cosθ)
• The amount of work done depends on the magnitude of the applied force, displacement of the body, and the angle between the displacement and force applied.
• Unit of work done: SI unit is Joule, smaller unit is erg.

Example Problem

• Pema pushes a box through a distance of 3m with a force of 100 N. The work done by Pema is calculated as: W = F x d = 100 x 3 = 300 J.