What Does 'Measuring Speed' Mean?
Speed tells us how quickly something moves — how much distance it covers in a given amount of time. To measure speed, we almost always need to measure two things: a distance and a time.
Speed is the distance travelled divided by the time taken. It tells us how fast an object is moving, regardless of direction.
The most common way to measure speed is to set up a fixed distance and measure the time it takes to travel that distance — which is essentially what a race is! By timing how long something takes to cover a known distance, we can calculate its speed.
Think about a school sports day sprint. You know the track is 100 m long, and you use a stopwatch to time each runner. That's all you need — distance and time — to figure out who ran fastest and how fast they went.
The Speed Equation
The relationship between speed, distance, and time is captured in a simple equation:
Where:
- distance is measured in metres (m)
- time is measured in seconds (s)
- speed is measured in metres per second, written as m/s or m s⁻¹
A useful memory trick: think of the equation as a triangle. Write D (distance) on top, and S (speed) and T (time) on the bottom. Cover the quantity you want to find:
- Cover D → Distance = Speed × Time
- Cover S → Speed = Distance ÷ Time
- Cover T → Time = Distance ÷ Speed
Many different units of speed exist in real life — miles per hour (mph) for cars, knots for ships, and even Mach numbers for supersonic fighter jets. In science, we usually work in metres per second (m/s).
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