A Useful Guide to Understanding Velocity, Acceleration, and Air Resistance

If you’ve been into a physics class recently or in the past, you might relate to the science of motion. You may have heard of terms like velocity, acceleration, and air resistance. Well, these are among the most basic concepts of physics, especially in a branch of classical mechanics called kinematics. Understanding these three concepts can help you improve your skills and have a better grasp of physics even without being a genius in mathematics.

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So, what do these terms mean, how do they relate to each other and why do they matter? Let’s walk together and answer these and more questions about velocity, acceleration, and air resistance in the brief guide below.

Defining Velocity, Air Resistance, and Acceleration 

As earlier mentioned, the three concepts are all applicable in motion physics and classical mechanics. If an object is falling from the 10th story of a building, for instance, it will be traveling at a specific velocity down towards the ground or the center of gravity. It will also accelerate as it goes down primarily against forces of air resistance.

Acceleration and velocity are specifically crucial in the study of motion, which is also known as kinematics. If you have some knowledge on kinematic equations, you must have come across acceleration (a), initial velocity (v0), and final velocity (v0) as variables. Together with time and displacement, the five variables make the different types of formulae used in motion calculations.

Let’s now define each of the three variables individually!

Air Resistance 

Air resistance basically refers to the opposing forces to the motion of an object while passing through the air. The motion could be downward, sideways, forward, or backward. Also known as drag forces, these forces tend to act against an object’s velocity while in motion, thus slowing it down by a significant margin. This is why the air resistance force or “the drag” largely depends on velocity. To calculate air resistance for any object in motion through a gas or fluid, the drag equation is used, usually expressed mathematically as:

FD = ½ ρv2 CDA. 

The variables in this equation are as follows:

  • FD – The drag force
  • ρ – Density of fluid
  • v – Speed of the object relative to the fluid
  • CD – Drag coefficient
  • A – Cross-sectional area

Velocity 

Velocity can simply be defined as the speed of an object in motion towards a specific direction. It is also defined as the rate at which a moving object changes position. As seen above, it is a crucial element in motion physics, which is why it’s a major variable in many of the equations used. The main difference between speed and velocity is that in the latter, a change in position has to be involved. In other words, velocity is more of a vector quantity where the direction is also an important factor.

Acceleration 

Finally, acceleration is another crucial vector quantity used in motion physics and the mathematical calculations involved. By definition, acceleration simply means the rate of change of an object’s velocity while in motion. If velocity is changing, the object is definitely accelerating. Most of you who drive can relate to this pretty well!

How air resistance impacts velocity and acceleration 

As earlier stated, air resistance or drag force basically depends on an object’s velocity. This is to say that, since an object’s velocity changes as it moves, the drag is not constant. Acceleration is also not constant since it also depends on velocity. However, constant acceleration is also possible, where the object changes velocity by an equal amount each second during motion.

The relationship between air resistance and velocity is often a bit complex, although the drag force increases with an increase in velocity. According to Stokes’ Law in physics, however, air resistance force and velocity are approximately proportional for very tiny objects. For bigger objects like cars and baseballs, on the other hand, air resistance is approximately equal to the velocity squared (v2).

Does Air Resistance Really Slow Things Down?  

Let’s take the classical example of an object falling down from the 10th story of a building earlier. If that object was a man in a parachute, it would take more time to land (safely) because the air molecules are pushing the huge surface area of the parachute up against gravity.

On the other hand, if that object was a human being, they would probably come down at an enormous speed and possibly break all their bones once they hit the ground. In essence, air resistance is a natural phenomenon designed to oppose movement by a significant margin. How much an object is slowed down will largely depend on an object’s:

  • Velocity
  • Shape
  • Size and surface area
  • Weight

In summary, velocity, acceleration, and air resistance are all related. They are all important elements of motion physics, especially when it comes to kinematic calculations. The above guide should help you understand each of them. 

Krystal | Sunny Sweet Days
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