seegongsik
Grade 6 (age 11-12)

grade 6 Speed

Speed tells how fast something moves: it is the distance covered in a set time, found by dividing the distance by the time taken. In 2 hours a car travels 120 km, so in 1 hour it covers 120 ÷ 2 = 60 km and its speed is 60 kilometers per hour, written 60 km/h. In the same time, the one that goes farther is faster; over the same distance, the one that takes less time is faster. The first picture marks where the car is after each hour as you change the distance and the time, and the second compares two speeds with bars.

What is speed?

🚗 Speed from distance and time
①In the same amount of time, the one that goes farther is faster
②Over the same distance, the one that takes less time is faster
③So speeds are compared by the distance covered in the same time, such as 1 hour, and that distance is the speed
④Speed = distance ÷ time; the distance covered in 1 hour gives kilometers per hour, and the distance covered in 1 second gives meters per second

Finding speed

120 km
2 h

Comparing two speeds

↔️ Comparing two speeds
①When two speeds are given, compare the numbers: the larger one is faster
②If A goes 60 km/h and B goes 80 km/h, in 2 hours A covers 120 km and B covers 160 km, a difference of 40 km
③To go the same 120 km, A takes 120 ÷ 60 = 2 hours and B takes 120 ÷ 80 = 1.5 hours
④The longer the bar, the farther it goes in 1 hour
60 km/h
80 km/h

Summary

Speed
Speed = distancetime
Measured in units such as km/h and m/s
Finding distance
Distance = speed × time
Multiply the speed by the time taken to get the distance
Finding time
Time = distancespeed
Divide the distance by the speed to get the time taken
🎯 Key points
①Speed = distance ÷ time, and the greater the speed, the faster
②Distance = speed × time, time = distance ÷ speed
③The distance covered in 1 hour is given in km/h, and in 1 second in m/s
④36 km/h means 10 m in 1 second, so it equals 10 m/s
⑤To compare speeds in different units, change them to the same unit first

Examples & Unit Review

Example 1
A car travels 240 km in 4 hours. What is its speed in km/h?
1
Speed = distance ÷ time = 240 ÷ 4.
2
240 ÷ 4 = 60, so the speed is 60 km/h.
▸ 60 km/h
Set the distance to 240 km and the time to 4 h and marks appear every 60 km, 4 of them, with the car standing at the 1-hour spot, 60 km.
Example 2
At 80 km/h, how far does a car go in 3 hours?
1
Distance = speed × time = 80 × 3.
2
80 × 3 = 240, so it goes 240 km.
▸ 240 km
Set the distance to 240 km and the time to 3 h and the speed comes out as 80 km/h, showing that the car covers 80 km in each hour.
Unit Review
How many hours does it take to travel 150 km at 50 km/h?
①3 hours
②2 hours
③5 hours
④100 hours
▸ ① 3 hours
1
Time = distance ÷ speed = 150 ÷ 50.
2
150 ÷ 50 = 3, so it takes 3 hours.
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Area of a Circle

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