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How Do You Calculate Change in Speed in Physics?

Published in Physics Speed Calculation 3 mins read

To calculate the change in speed in physics, you subtract the initial speed from the final speed.

In physics, the change in speed is a straightforward calculation. It represents how much faster or slower an object is moving compared to a previous point in time. The fundamental formula for calculating this change is derived from the difference between the object's final speed and its initial speed.

Understanding the Formula

The most common way to calculate the change in speed is given by the simple equation:

Change in Speed = Final Speed - Initial Speed

As stated in a reference from 02-Nov-2015, "vFINAL−vINITIAL= change in speed."

Here's what the terms mean:

  • vFINAL: This is the speed of the object at the end of the time period you are considering.
  • vINITIAL: This is the speed of the object at the beginning of the time period you are considering.

The result tells you how much the speed has increased (if the result is positive) or decreased (if the result is negative) over that interval.

Practical Examples

Let's look at a couple of examples to illustrate how this works:

  1. Scenario 1: Speeding Up

    • An object starts moving at an initial speed of 10 meters per second (m/s).
    • After a few seconds, its final speed is 25 m/s.
    • Change in Speed = vFINAL - vINITIAL
    • Change in Speed = 25 m/s - 10 m/s
    • Change in Speed = 15 m/s
    • Interpretation: The object's speed increased by 15 m/s.

  2. Scenario 2: Slowing Down

    • A car is initially traveling at 30 meters per second (m/s).
    • It then slows down to a final speed of 12 m/s.
    • Change in Speed = vFINAL - vINITIAL
    • Change in Speed = 12 m/s - 30 m/s
    • Change in Speed = -18 m/s
    • Interpretation: The object's speed decreased by 18 m/s. The negative sign indicates a reduction in speed.

Key Points to Remember

  • Change in speed is a scalar quantity, meaning it only tells you how much the speed changed, not the direction.
  • Units for speed are typically meters per second (m/s) in physics, but could also be kilometers per hour (km/h), miles per hour (mph), etc. Ensure your initial and final speeds are in the same units.
  • This calculation is a fundamental part of understanding concepts like acceleration, which is the rate of change of velocity (and thus speed, in simple cases).

Calculating the change in speed is a basic but essential skill in physics for analyzing the motion of objects.

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