GCSE Physics Tutorial: Calculating Average Speed from Non-Uniform Motion
In the realm of physics, average speed is a valuable concept that enables us to understand the overall rate of motion of an object, even if its speed is not constant. When dealing with non-uniform motion, where the speed changes over time, calculating the average speed becomes essential to characterise the overall behaviour. In this tutorial, we'll explore how to calculate average speed from non-uniform motion.
Average Speed vs. Instantaneous Speed
Before delving into non-uniform motion, it's important to differentiate between average speed and instantaneous speed:
Average Speed: This is the total distance traveled divided by the total time taken. It gives a sense of the overall pace of motion over a specific interval.
Instantaneous Speed: This is the speed of an object at a particular instant in time. It can vary greatly during non-uniform motion.
Calculating Average Speed from Non-Uniform Motion
When dealing with non-uniform motion, where the speed changes over time, calculating the average speed involves determining the total distance traveled and the total time taken. Here's how you can do it:
Divide the Motion into Intervals: If the motion is not uniform, divide the entire motion into smaller intervals where the speed is relatively constant. For each interval, determine the distance traveled and the time taken.
Calculate the Average Speed for Each Interval: For each interval, calculate the average speed using the formula:
Average Speed (v) = Distance (d) / Time (t)
Total Distance and Total Time: Sum up the distances and times for all intervals to find the total distance (D) and total time (T).
Calculate the Overall Average Speed: Divide the total distance by the total time to calculate the overall average speed:
Overall Average Speed = Total Distance (D) / Total Time (T)
Example Calculation
Let's consider a scenario where a cyclist covers 20 km at 15 km/h for the first 2 hours, and then speeds up to 25 km/h for the next 1 hour. To calculate the average speed:
For the first interval: Average Speed = 20 km / 2 h = 10 km/h
For the second interval: Average Speed = 25 km / 1 h = 25 km/h
Total Distance = 20 km + 25 km = 45 km Total Time = 2 h + 1 h = 3 h
Overall Average Speed = 45 km / 3 h = 15 km/h
The cyclist's average speed over the entire journey is 15 km/h.
Summary
Calculating average speed from non-uniform motion involves breaking down the motion into intervals, calculating average speeds for each interval, and then determining the overall average speed based on the total distance and total time. This approach allows us to describe the overall pace of an object's movement, even when its speed is not constant.
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