Why Do We Feel Acceleration, But Not Constant Speed? The Science Explained

Have you ever wondered why you can feel the sudden jolt of a car accelerating but not the constant speed of an airplane cruising at 30,000 feet? This intriguing question touches on fundamental principles of physics that govern our everyday experiences. By the end of this post, you'll have a clear understanding of why we feel acceleration but not velocity, and how these concepts shape our perception of motion.

Understanding the Basics: Acceleration vs. Velocity

Velocity is the rate of change of an object's position. It also has both magnitude and direction but remains constant if no external force acts upon it. When you are moving at a constant velocity, you do not feel any force because your state of motion is unchanging.

Acceleration is, in the other hand, the rate at which an object's velocity changes over time. It is a vector quantity, meaning it has both magnitude and direction. When you feel a push or a pull, you are experiencing acceleration. This happens because a force is being applied to you, changing your velocity.

Velocity vs Speed

When describing the motion of objects in terms of distance, time, and direction, physicists use the basic quantities of speed and velocity. Two terms, two distinct meanings. Yet, not uncommonly, we hear these terms used interchangeably. So, what’s the difference? Why is it incorrect to use the terms speed and velocity interchangeably?

The reason is simple. Speed is the time rate at which an object is moving along a path, while velocity is the rate and direction of an object’s movement. Put another way, speed is a scalar value, while velocity is a vector. For example, 50 km/hr (31 mph) describes the speed at which a car is traveling along a road, while 50 km/hr west describes the velocity at which it is traveling.

Why We Feel Acceleration

When you are in a car that suddenly accelerates, you feel a force pushing you back into your seat. This sensation occurs because your body initially resists the change in motion due to inertia. Inertia is the tendency of an object to resist changes in its state of motion. As the car accelerates, the seat pushes against your body, causing you to accelerate along with the car.

Similarly, when an airplane takes off, you feel the force of acceleration as the engines propel the plane forward. This force is transmitted through the seat, making you aware of the change in velocity. Once the plane reaches cruising speed, the acceleration ceases, and you no longer feel this force.

The Role of Inertia

Inertia plays a crucial role in why we do not feel constant velocity. According to Newton's First Law of Motion, an object in motion will remain in motion at a constant velocity unless acted upon by an external force. When an airplane is cruising at a constant speed, there is no net force acting on you to change your state of motion. As a result, you feel as if you are stationary, even though you are moving at hundreds of kilometers per hour.

The Vestibular System: Our Inner Sense of Motion

Our ability to sense acceleration is largely due to the vestibular system in our inner ear. This system helps us maintain balance and spatial orientation by detecting changes in motion and position. When you accelerate, the fluid in your inner ear shifts, sending signals to your brain that you are moving. However, when you are moving at a constant velocity, the fluid remains stable, and no signals are sent, making you unaware of the motion.

Practical Examples: Airplanes and Cars

Consider a flight at 30,000 feet. When the plane is cruising at a constant speed of 900 km/h, you feel no sensation of speed. However, during takeoff or turbulence, the changes in velocity cause you to feel acceleration. Similarly, in a car, you feel the force when the car speeds up or slows down, but once it reaches a steady speed, the sensation disappears.

Conclusion: The Wonders of Motion

Understanding why we feel acceleration but not velocity provides insight into the fundamental principles of physics that govern our world. It highlights the role of forces, inertia, and our vestibular system in shaping our perception of motion. Next time you experience the jolt of acceleration or the smoothness of constant velocity, you'll have a deeper appreciation for the science behind these sensations.

By FreeAstroScience.com, where we simplify complex scientific principles for enthusiasts like you.