117
Movement and speed
Textbook: Part 4, lesson 117, pp. 22–24
GoalThe idea of speed: distance travelled in one unit of time; units of speed; finding the speed.
New words
speed · tezlikdistance travelled · bosib o‘tilgan yo‘ldistance · masofakilometres per hour · km/soat
Explanation
Speed is the distance travelled in one unit of time (1 hour, 1 minute, 1 second). If a car goes 60 km in 1 hour, its speed is 60 km/h. If a child walks 70 m in 1 minute, the speed is 70 m/min. To find the speed we divide the distance by the time: v = s : t. In our problems we take the speed to be constant.
Worked examples
A bus travelled 200 km in 4 hours. v = 200 : 4 = 50 km/h.
A swimmer swam 100 m in 50 seconds. v = 100 : 50 = 2 m/s.
Class activity
“Measure the speed”: mark 10 m in the classroom or yard. Children take turns walking it, time themselves with a stopwatch and find their speed in m/s.
Practice
1
A train travelled 400 km in 5 hours. What is its speed in km/h?
80
2
A runner ran 1 200 m in 6 minutes. What is the speed in m/min?
200
3
A pigeon flew 180 km in 3 hours. What is its speed in km/h?
60
4
A tractor covered 48 km in 4 hours. What is its speed in km/h?
12