Uniformly Accelerated Motion

Kinematics is the branch of physics that studies the motion of a body or system without reference to force or acceleration.

The term Kinematics began usage in the mid-19th century and comes from the greek kinemat which means "motion."

One of the best examples of Kinematics would be uniform accelerated motion where uniform means constant or motion with constant acceleration.

Motion with constant acceleration is best demonstrated by an object free falling at the surface of the earth. An object in free fall would only be under the force of Gravity. Air resistance plays a very minor role in free fall since unless the fall was happening at an incredible distance the air resistance would be small.

The force of gravity:

g = 9.80 m/s^2 = 32.2 ft/s^2

When an object is in free fall you can measure the time it takes to fall a distance and determine the acceleration on the object due to gravity.

A free fall apparatus can be used to determine the precise time it takes to travel a certain distance so the acceleration can be determined.

There are a few devices that can be used as distance-time measurement devices.

There is a digital free-fall apparatus that measures the distance an object is dropped from a set point on a stand and the time is given from a digital device that works similar to a stopwatch beginning when the fall begins and ending when the object lands on a sensor.

There is the picket-fence method that drops a transparent piece of plastic that has been marked with evenly spaced dashes, as the plastic is dropped through a photogate the time is measured. Similar to the digital device the distance would be logged down prior to the drop.

A free-fall spark timer simply consists of a metal object that falls freely between two wires with some specially treated paper strip between the object and the wire. A spark timer is a fast timing device that give off high voltage across the wires at preset intervals.

The high voltage between the wires jumps as the object travels and leaves markings on the paper strip that give the intervals of time at certain distances.

All of the devices above give the time that the object takes to reach certain distances. These functions can then be used in the following equation:

vi = instantaneous velocity

yi = distance

ti = time

vi = 2yi/ti

On most of your air track systems a blower supplies air to the interior of a hollow track and is forced out of small holes in the track.

A car or glider travels on a cushion of air provided which reduces friction. Since the friction is all but removed the car will be mocign at a constant acceleration similar to a free fall.

The car is influenced by gravity as the open end of the air track is elevated on a block.

A photogate is used for automatic timing. If using an air track without a photogate a stopwatch can be used to determine time.

The time it takes to go a certain distance is recorded and the following equation can be used to determine vi:

vi = 2yi/ti

Using a Free Fall Apparatus or a Linear Air Track allows one to visualize Newton's Second Law:

The acceleration of an object is directly proportional to the resultant force acting on it and inversely proportional to its mass. The direction of the acceleration is the direction of the resultant force.

Enjoy your devices and making your calculations and enjoy the experience of free falling.