Converting km per hour to cm per second using JavaScript

We are required to write a JavaScript function that takes in a number that specifies speed in kmph and it should return the equivalent speed in cm/s.

Understanding the Conversion

To convert km/h to cm/s, we need to understand the relationship:

• 1 kilometer = 100,000 centimeters
• 1 hour = 3,600 seconds
• Formula: km/h × (100,000 cm / 1 km) × (1 hour / 3,600 seconds)

Example

Following is the code:

const kmph = 12;

const convertSpeed = (kmph) => {
    const secsInHour = 3600;
    const centimetersInKilometers = 100000;
    const speed = Math.floor((kmph * centimetersInKilometers) / secsInHour);
    return `Equivalent in cm/s is: ${speed}`;
};

console.log(convertSpeed(kmph));

Equivalent in cm/s is: 333

More Precise Conversion

For better accuracy, we can return the decimal value instead of using Math.floor():

const convertSpeedPrecise = (kmph) => {
    const secsInHour = 3600;
    const centimetersInKilometers = 100000;
    const speed = (kmph * centimetersInKilometers) / secsInHour;
    return parseFloat(speed.toFixed(2));
};

console.log(convertSpeedPrecise(12));    // 12 km/h
console.log(convertSpeedPrecise(36));    // 36 km/h
console.log(convertSpeedPrecise(5.5));   // 5.5 km/h

333.33
1000
152.78

Simplified One-Line Function

We can also create a more concise version:

const kmphToCmps = (kmph) => (kmph * 100000) / 3600;

console.log(kmphToCmps(18));  // 18 km/h to cm/s
console.log(kmphToCmps(72));  // 72 km/h to cm/s

500
2000

Verification

Let's verify our conversion with a known example:

// 36 km/h should equal 1000 cm/s
const speed = 36;
const result = (speed * 100000) / 3600;
console.log(`${speed} km/h = ${result} cm/s`);

36 km/h = 1000 cm/s

Conclusion

Converting km/h to cm/s involves multiplying by 100,000 (cm per km) and dividing by 3,600 (seconds per hour). The simplified formula is: cm/s = km/h × (100,000 ÷ 3,600).