Speed vs Acceleration
Speed and acceleration are common terms that are encountered by students studying motion in physics. These are the terms that are also used in daily life and those who do not know the difference are often confused and use the terms interchangeably which is incorrect.. This article will explain the two terms and how they are related so as to make the concepts clear for everyone.
Speed is the distance covered by a moving object per unit of time. It is simply how fast an object is moving without regards to direction. This means it is a scalar quantity. If you are driving a car, the speedometer tells you the speed of the car all the time. Simply divide the distance covered by a moving object with time taken and you know the speed of the object. A similar concept is velocity which is same as speed but it takes into consideration the direction of motion also. Thus speed is magnitude of velocity, which also has direction.
Acceleration is another concept which is rate of change of speed, specifically its velocity. Thus it is a vector quantity as it involves velocity and not speed. If a car is moving at a constant speed, it is said to have no acceleration. Once you push down the paddle called accelerator, the speed of the car increases and it is said to be accelerating. If a person is running on a circular track at a constant speed, he is said to have acceleration though his speed is not changing. This is because his direction is changing all the time and since acceleration is a vector quantity, change of direction means the person has acceleration.
The SI unit of speed is m/sec. Since acceleration is rate of change of velocity, SI unit of acceleration is meters/second². It is clear with above discussion that to induce acceleration in a moving object, either its speed or its direction needs to be altered. There is another related concept known as deceleration which is when a moving object gradually or abruptly comes to rest. When you apply brakes in a moving car, its speed gradually decreases and it is said to have a negative acceleration.
In brief: • Speed and acceleration are related but different concepts. • While speed is distance covered in a unit of time, acceleration is the rate of change of speed that also takes into consideration direction.

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