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An introduction to how fast objects move and the mathematical formula used to measure it.
If a cheetah and a professional sprinter both ran for exactly 10 seconds, how would you prove who was truly faster without a side-by-side race?
Speed is a measure of how fast an object moves. In physics, we describe it as the rate of change of distance. Think of it as a 'distance-per-time' ratio. If you walk 5 meters every single second, your speed is constant. If you cover more distance in the same amount of time, you are moving faster. It is important to note that speed is a scalar quantity, meaning it only tells us 'how fast' and does not care about the direction of travel. Whether you run North or South, if you cover the same ground in the same time, your speed is identical.
Quick Check
If two cars travel for 1 hour, but Car A travels 60 km and Car B travels 80 km, which car has the higher speed?
Answer
Car B has the higher speed because it covered more distance in the same amount of time.
A turtle crawls meters across a garden. It takes the turtle seconds to finish the trip. What is the turtle's speed?
1. Identify the distance: . 2. Identify the time: . 3. Apply the formula: . 4. Calculate the result: .
In science, we use the International System of Units (SI) to ensure everyone is speaking the same 'math language.' The standard unit for distance is the meter () and the standard unit for time is the second (). Therefore, the standard SI unit for speed is meters per second, written as . While you might see kilometers per hour () on a car's speedometer or miles per hour () in some countries, scientists almost always convert these to for calculations.
A cyclist travels meters to reach a park. If the trip takes seconds, what is the cyclist's average speed?
1. List your variables: , . 2. Set up the equation: . 3. Simplify the fraction: . 4. Final Answer: .
Quick Check
What does the 's' stand for in the unit ?
Answer
The 's' stands for seconds, which is the SI unit for time.
A delivery drone flies at a constant speed of . How far will it travel if it flies for minutes?
1. Identify knowns: , . 2. Critical Step: Convert time to SI units. . 3. Rearrange the formula to find distance: . 4. Calculate: . 5. Final Answer: .
Which of the following is the correct SI unit for speed?
If a car travels meters in seconds, what is its speed?
If you increase the time it takes to cover a distance, the speed increases.
Review Tomorrow
In 24 hours, try to write down the speed formula from memory and explain what each letter () stands for.
Practice Activity
Next time you are in a car or bus, pick two landmarks. Use a stopwatch to see how many seconds it takes to pass them, and ask an adult for the distance to calculate the average speed!