seegongsik
Grade 5 (age 10-11)

grade 5 Motion of Objects

We compare how fast things move by how far they go in the same time, or how little time they take to cover the same distance. Speed puts that into a single number: the distance travelled divided by the time taken. People walk about 4 km in an hour, a bicycle goes about 15 km, and a car in town about 40 to 60 km. Change the speed to see how many meters the car covers each second; in the graph below, the faster the speed, the steeper the distance-time line.

How fast? Speed

40 km/h
🚗 What speed means
①Speed is the distance an object travels in one unit of time.
②Of two objects moving for the same time, the one that goes farther is faster.
③Common units are km/h (kilometers in an hour) and m/s (meters in a second).
④A car going 40 km/h covers about 11 m every second.

Working out speed

Formula for speed
Speed = DistanceTime
Running 100 m in 20 seconds gives a speed of 100 ÷ 20 = 5 m/s.
A worked example
300 km in 3 h → 3003 = 100 km/h
A KTX train reaches about 300 km/h at its fastest; a car in town goes about 40 to 60 km/h.
💡 Comparing how fast
①Over the same distance, the shorter the time, the faster. That is how a race works.
②Over the same time, the longer the distance, the faster.
③If both distance and time are different, work out the speeds and compare them.

Reading a distance-time graph

📊 Motion on a graph
①The horizontal axis is time and the vertical axis is distance.
②A straight line means the object moves at a steady speed.
③The steeper the line, the farther it goes in the same time, so the faster it is.
④A flat line means the distance stays the same as time passes, so the object is standing still.

Summary

Speed in one line
Speed = DistanceTime
Always write a unit with a speed. km/h and m/s are different sizes (1 m/s = 3.6 km/h).
🎯 Key points
①Speed = distance travelled ÷ time taken.
②Over the same distance, a shorter time means faster.
③Over the same time, a longer distance means faster.
④On a distance-time graph, a steeper line means a higher speed.
⑤Walking is about 4 km/h, cycling about 15 km/h, and a car in town about 40 to 60 km/h.

Examples and Unit Test

Example 1
A person runs 100 m in 20 seconds. What is their speed in m/s?
1
Speed is found by dividing the distance travelled by the time taken.
2
100 m ÷ 20 s = 5 m/s.
▸ 5 m/s
In km/h that is 5 × 3.6 = 18 km/h, about as fast as a bicycle.
Example 2
A car travels 300 km in 3 hours. What is its speed? And on a distance-time graph, what happens to the line as speed increases?
1
Speed = 300 km ÷ 3 h = 100 km/h.
2
A faster object goes farther in the same time, so its line on the graph climbs more steeply.
▸ 100 km/h, and the line gets steeper.
Raise the speed to 100 km/h in the graph and the line is far steeper than the dashed walking line.
Unit-test style
Which statement about the motion of objects is correct?
①Speed is found by dividing the time taken by the distance travelled.
②Over the same distance, the shorter the time taken, the faster the speed.
③On a distance-time graph, a gentler line means faster.
④Speed is measured in kg.
⑤A flat line on a distance-time graph means the object is moving fast.
▸ ② Over the same distance, the shorter the time taken, the faster the speed.
1
Speed is distance divided by time, so for the same distance a shorter time gives a higher speed.
2
Speed is distance ÷ time (①), a steeper line means faster (③), speed is measured in m/s or km/h (④), and a flat line means standing still (⑤).
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