Understanding speed, velocity, and acceleration by analogies

The concept of speed, velocity and acceleration is what we are experiencing in our daily life. From rolling a ball, to riding a bike, to boarding a train, we are all experiencing the effect of speed, velocity, and acceleration, so it not just a mathematically proven fact, like the special theory of relativity.

When basic physics parameters like this is explained by analogies, it helps students to get a clearer picture of what is really happening and how it affect us. In this post, we will explore series of analogies that will help us understand some of these elementary parameters of physics.

But first, there are two more things we have to understand. There are the two types of physical quantities - SCALAR and VECTOR

SCALAR - when just the magnitude is enough (i.e the size or just the number).

For example, my height is 80cm, the temperature is 30degrees, distance between California and Texas is 500km.

VECTOR - When direction and magnitude are both required for understanding. For example, the velocity of the car I saw was 30km/hr toward North, I applied 40N force on the bench downwards.

Now we've understand what scalar and vector are, let proceed to our main business. 

Speed: Speed is defined as the rate of change of distance moved with time. Speed, as a scalar quantity has a property of magnitude(size) but no direction. For example an object moving at a speed of 40ms^-1  has an higher speed than one moving at a speed of 20ms^-1 .

Velocity: Velocity is defined as the rate of change of distance moved with time(or the rate of change of displacement with respect to time) in a specified direction. The term velocity is not the same as speed. It has both magnitude and direction. Hence it is a vector quantity.

Acceleration: Acceleration is defined as the rate of change of velocity with respect to time.  Acceleration is the second derivative of displacement.

Speed and velocity are pretty much the same thing, with just one difference. Direction. If you assign a direction to speed, it becomes velocity. So now we know the theoretical definition of speed, velocity and acceleration. Let now move to the practical definition of it.

Speed: Speed is simply how fast an object is moving. Let use a roller coaster analogy. As we all know that a roller coaster moves in a circular and directionless manner. So it has just speed but no velocity. So we can say that the rollar coaster moves at the speed of 12m/s or the speed increases to 30m/s. That's just it, no direction is needed to understand.

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Velocity: Velocity has to do with how fast an object is moving towards a given direction. For example if your boarding a train towards the East, the speed of the train could be just 300km/hr, but if you were to specify the direction, you will say that the velocity of the train is 300km/hr towards North. Now there is direction. 

Sometimes speed and velocity are often used interchangeably, you might often hear that a car was moving at a velocity of 20m/s or so. It all the same, but when asked for velocity, always try to include the direction.

Acceleration: Acceleration refers to how fast an object switches it speed in a time duration. Consider a car at rest, when you start the engine and hold the accelerator peddal, even if you put it at the highest speed you will still notice that it will take time before the car will start moving at it highest speed, it will start slowly untill it begins to move faster.