<< Chapter < Page Chapter >> Page >
By the end of this section, you will be able to:
  • Use the kinematic equations with the variables y and g to analyze free-fall motion.
  • Describe how the values of the position, velocity, and acceleration change during a free fall.
  • Solve for the position, velocity, and acceleration as functions of time when an object is in a free fall.

An interesting application of [link] through [link] is called free fall , which describes the motion of an object falling in a gravitational field, such as near the surface of Earth or other celestial objects of planetary size. Let’s assume the body is falling in a straight line perpendicular to the surface, so its motion is one-dimensional. For example, we can estimate the depth of a vertical mine shaft by dropping a rock into it and listening for the rock to hit the bottom. But “falling,” in the context of free fall, does not necessarily imply the body is moving from a greater height to a lesser height. If a ball is thrown upward, the equations of free fall apply equally to its ascent as well as its descent.


The most remarkable and unexpected fact about falling objects is that if air resistance and friction are negligible, then in a given location all objects fall toward the center of Earth with the same constant acceleration , independent of their mass . This experimentally determined fact is unexpected because we are so accustomed to the effects of air resistance and friction that we expect light objects to fall slower than heavy ones. Until Galileo Galilei (1564–1642) proved otherwise, people believed that a heavier object has a greater acceleration in a free fall. We now know this is not the case. In the absence of air resistance, heavy objects arrive at the ground at the same time as lighter objects when dropped from the same height [link] .

Left figure shows a hammer and a feather falling down in air. Hammer is below the feather. Middle figure shows a hammer and a feather falling down in vacuum. Hammer and feather are at the same level. Right figure shows astronaut on the surface of the moon with hammer and a feather lying on the ground.
A hammer and a feather fall with the same constant acceleration if air resistance is negligible. This is a general characteristic of gravity not unique to Earth, as astronaut David R. Scott demonstrated in 1971 on the Moon, where the acceleration from gravity is only 1.67 m/s2 and there is no atmosphere.

In the real world, air resistance can cause a lighter object to fall slower than a heavier object of the same size. A tennis ball reaches the ground after a baseball dropped at the same time. (It might be difficult to observe the difference if the height is not large.) Air resistance opposes the motion of an object through the air, and friction between objects—such as between clothes and a laundry chute or between a stone and a pool into which it is dropped—also opposes motion between them.

For the ideal situations of these first few chapters, an object falling without air resistance or friction is defined to be in free fall    . The force of gravity causes objects to fall toward the center of Earth. The acceleration of free-falling objects is therefore called acceleration due to gravity    . Acceleration due to gravity is constant, which means we can apply the kinematic equations to any falling object where air resistance and friction are negligible. This opens to us a broad class of interesting situations.

Questions & Answers

what is a wave?
show that coefficient of friction of solid block inclined at an angle is equivalent to trignometric tangent of angle
thanks for that definition.
Dodou Reply
Hi everyone please can dere be motion without force?
whats is schrodinger equation
l went spiral spring
what is position?
Adhar Reply
position is simply where you are or where you were
position is the location of an object with respect to a two or three dimensional axes or space.
Can dere be motion without force?
what is the law of homogeinity?
auson Reply
two electric lines of force never interested each other. why?
Sujit Reply
proof that for BBC lattice structure 4r\root 5 and find Apf for the BBC structure
Eric Reply
what is physics?
Abdulaziz Reply
physics is deine as the specific measrument of of volume, area,nd distances...
if a string of 2m is suspended an an extended 3m elasticity is been applied.... is hooks law obeyed?
if a string of 2m is suspended an an extended 3m elasticity is been applied.... is hooks law obeyed?
proof that for a BBC lattice structure a= 4r/ root 5 find the APF for the BBC structure
if a string of 2m is suspended an an extended 3m elasticity is been applied.... is hooks law obeyed?
Enyia Reply
tell me conceptual quetions of mechanics
Syeda Reply
I want to solve a physical question
a displacement vector has a magnitude of 1.62km and point due north . another displacement vector B has a magnitude of 2.48 km and points due east.determine the magnitude and direction of (a) a+ b and (b) a_ b
Kou Reply
use Pythogorous
A student opens a 12kgs door by applying a constant force of 40N at a perpendicular distance of 0.9m from the hinges. if the door is 2.0m high and 1.0m wide determine the magnitude of the angular acceleration of the door. ( assume that the door rotates freely on its hinges.) please assist me to d
what is conditions met to produce shm
Enocy Reply
what is shm
Why is Maxwell saying that light is an electromagnetic wave?
1st condition; It(th e BBC's system) must have some inertia which will enable it to possess Kinetic energy 2. must be able to store potential energy
I meant "the system" not the BBC'S....."
what a answer bro
kindly tell us the name of your university
GUlam Ishaq Khan INSTITUTE of engineering science
Department of Environment Ionian University Zante Greece
why light wave travel faster than sounds
ALI Reply
Why light travel faster than sounds?
Light travel faster than sound because it does not need any medium to travel through.
when an aeroplane flies....why it does not fall on the earth?
As an aeroplane moves, it hits a wind,we have the wind flowing at the upper and lower zone of the aeroplane, the one that is moving on the upper zone moves at a greater speed than that of the lower zone, this creates a low pressure on the upper zone and a greater pressure at the lower zone.
which thing of aeroplane moves it upward?
good question
about force
am pleased to join the group
It a privilege to be here
Light speed is more than sound speed. C=3×10*8m/s V=320-340 m/s
A body of mass 2kg slides down a rough plane inclined to horizontal at 30degrees. find the energy that is wasted as a result of friction if the co-efficient of kinetic f
official Reply
ten applications of Newton's second law of motion
Alale Reply
Calculate the volume at S.T.P of a gas whose volume at -5° and 746 mmHg
Mlungisi Reply
Practice Key Terms 2

Get the best University physics vol... course in your pocket!

Source:  OpenStax, University physics volume 1. OpenStax CNX. Sep 19, 2016 Download for free at http://cnx.org/content/col12031/1.5
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'University physics volume 1' conversation and receive update notifications?