Falling Objects

FALLING OBJECTS

From what you already know about the physics of motion in one direction, you can solve the problems related to falling objects. In such cases, there is a constant acceleration, independent of the mass of the object—unless you factor in things like air resistance. Without this effect of air resistance, heavy objects will fall at the same rate as lighter objects. In the real world, air resistance does play a role in the velocity of a fall but, for short distances, it is negligible. “Free fall” is what the fall of an object is called when there is no friction or air resistance involved.

According to the force of gravity, objects will fall toward the center of the Earth. In actuality, this “force of gravity” is nothing more than “acceleration”. It turns out that acceleration is a constant and is based on the mass of the earth. While it is an acceleration number, it is given the symbol “g”. It is considered as a constant on any place on the earth. On earth, it is a constant of 9.8 meters per second squared.

In reality, gravity varies slightly depending on altitude, latitude, local topography, and the presence of underlying geological formations. The direction, however, will always be in the direction of the center of the earth. We call it a “vertical” drop even though it is actually toward the earth’s center. If the coordinate system is used, this acceleration will be a negative number as the objects are accelerating in a downward fashion. In some cases, the coordinate system is reversed so that the force of gravity and all directions are considered positive.

Velocity in these circumstances is considered vertical in nature. If an object is dropped, the initial velocity is said to be zero and the object is in free-fall. Motion will be in one direction and the acceleration will always be a constant, which is 9.8 meters per second squared.

The kinematic equations you should know for objects related to falling are described in figure 2. In such cases, acceleration is considered to be -g:

Figure 2.

In cases where an object is thrown upward, the velocity is positive because the direction of the object is up and up is a positive direction. Because gravity will oppose the throwing upward of an object, this will be a negative value as the object’s acceleration due to gravity opposes its upward velocity. If an object is thrown downward, the velocity will be negative and the force of gravity will be negative as well but will be of the same side in that they are working in the same direction.

While it generally isn’t necessary, experiments can be done to determine the exact force of gravity at a specific point on earth. A small metal ball can be dropped and the time it takes to drop a certain distance can be measured. Using the equations in figure 2, the force of gravity can be calculated. Again, you need to choose the coordinates so that up is positive and g is negative in most situations; however, you can reverse that entirely so that the downward direction is positive and the acceleration due to gravity is positive.