# How is gravity related to terminal velocity?

The greatest velocity (speed) attained by an item as it descends through a fluid is referred to as terminal velocity (air is the most common example). It happens when the total of the drag force (Fd) and buoyancy (B) exerted on the item equals the downward force of gravity (FG). The greater the mass of the item, the faster it will fall.

Gravity is the number one force behind why objects fall. At any given moment, every object in the universe is falling toward the center of earth at 9.8 m/s2. Objects with more mass fall faster than objects with less mass; this is called gravity's "inverse square law." But there are other forces at work too! Air resistance is another factor that can slow down or stop an object's descent.

Air resistance is the force that prevents airplanes from flying right off the ground. It comes from molecules in the air hitting the surface of the airplane and pushing it back up. Just like humans need food to breathe, animals need air to live. So too does an object need oxygen to burn fuel cells which generate electricity that power devices such as lights and motors. Without oxygen, those devices would not function properly and people would not be able to see or ride electric scooters either!

As an object falls through the air, it encounters air molecules that are moving away from each other.

## Is terminal velocity the same as settling velocity?

The drag, or force of resistance, will eventually equal the gravitational attraction on the item at some speed (buoyancy is considered below). At this moment, the item ceases to accelerate and continues to descend at a steady speed known as the terminal velocity (also called settling velocity). This is also the maximum horizontal distance that it can travel before it stops moving altogether.

As an example, if an object with mass 0.5 kg is dropped from a height of 2 m, then it will reach its terminal velocity of about 110 km/hr. If the object is not dropped, but instead allowed to fall under its own weight, then it will reach a speed of about 10 m/s, or 100 km/hr. The difference between these two speeds is called the deceleration rate and is equal to 10 m/s2 - 100 km/hr2 = 9.8 m/s-1.

Thus, we can say that the object's terminal velocity is 90% of its initial falling speed. It is important to note that this is a theoretical number based on very simple assumptions. In reality, the object will slow down more because there is friction between itself and the surrounding air molecules. However, even with this extra factor taken into account, the object still reaches about 70% of its initial falling speed.

## Is terminal velocity based on weight?

The weight of the object influences the air drag force on it and, as a result, its final velocity. The greater the weight, the faster it will fall.

However, the distance that an object falls is also related to its height. So, if we know the height of the object, then we can calculate its final speed. The higher the object, the more distance it will travel before hitting the ground.

Since height is important in calculating terminal velocity, it makes sense that the object being dropped would be measured along with its weight so that both values are known. This allows for the calculation of terminal velocity.

For example, if we were to drop a 100 g ball from 1 m above floor level, its terminal velocity would be approximately 56 km/hr. However, if we were to drop the same ball from 2 m above floor level, its terminal velocity would be approximately 70 km/hr.

As you can see, increasing the height of the object increases its terminal velocity. This is because objects at higher heights fall for a longer time until they reach floor level.

Also, notice that the heavier the object, the slower it falls.

## What forces act on an object at terminal velocity?

Objects falling through a fluid achieve terminal velocity. Because the resultant force exerted on the item is zero at terminal velocity, it moves at a constant speed in a constant direction. The only force acting on the item at this point is the air resistance that opposes its motion.

At terminal velocity, the object's weight is balanced by the drag force of air resistance. The greater the object's mass, the more force is needed to overcome air resistance and bring it down to earth. Objects such as rocks, for example, have very little surface area relative to their mass, which means they require a large amount of force to be accelerated or decelerated.

The maximum speed an object can travel with no additional force is called its "terminal velocity." At this point, the object reaches equilibrium between the force of gravity and the force of air resistance. For objects of similar shape and size, the air resistance force is proportional to their surface area. So, for two objects of different sizes, an object that is traveling at its terminal velocity will be moving at the same speed regardless of its size.

If something has a mass much larger than air, such as Earth, then it would not reach terminal velocity when falling from a height. Instead, it would keep on accelerating until it hit the ground.

##### Nancy Martin

Nancy Martin has been working in the education field for over 20 years. She has experience in both public and private schools. Nancy loves working with children and finds inspiration in their curiosity and desire to learn.