What Is Speed?

Core Idea

Speed tells you how fast something is moving. It measures how much distance an object covers in a certain amount of time. A car going 60 miles per hour covers 60 miles in one hour. If something covers more distance in the same amount of time, it has a higher speed. Speed is always described using a distance and a time, like miles per hour or meters per second.

How It's Best Learned

Time students walking, jogging, and running across a set distance. Calculate speed together as distance divided by time. Compare the speeds of different toy cars on a ramp using a stopwatch and measuring tape.

Common Misconceptions

• Speed and distance are the same thing. (Speed includes time — it is how far you go in a certain amount of time.)
• A faster object always travels a longer distance. (Only if both objects travel for the same amount of time.)
• If an object is moving, its speed is always constant. (Most objects speed up and slow down as they move.)
• Speed only applies to cars and runners. (Everything that moves has a speed, from a snail to a planet.)

Explainer

When you watch a race, you can usually tell who is the fastest — they are the one out in front. But how do we put a number on "fast"? That is where speed comes in. Speed tells you exactly how much distance an object covers in a certain amount of time. If you walk 4 blocks in 10 minutes, your speed is a lot slower than a bike that covers 4 blocks in 2 minutes.

To find speed, you divide the distance traveled by the time it took. If a runner goes 200 meters in 40 seconds, their speed is 200 ÷ 40 = 5 meters per second. That means every single second, the runner covers 5 meters. Speed always has two parts: a distance unit and a time unit. You might hear miles per hour for cars, meters per second in science class, or even inches per minute for a snail.

Not everything moves at the same speed the whole time. When a car starts from a stop sign, it goes slowly at first and then gets faster. When scientists talk about average speed, they mean the total distance divided by the total time for the whole trip. Your average speed on a car ride might be 30 miles per hour, even though sometimes you were going 50 and sometimes you were stopped at a light.

Speed is one of the most useful ideas in science because it connects distance and time — two things you can easily measure. With just a ruler and a stopwatch, you can figure out the speed of almost anything. Once you understand speed, you can start asking bigger questions, like why some objects speed up, what forces make them slow down, and how to predict where something will be in the future.