2
Space and time
Textbook: pp. 11–13
GoalKnow the ideas of space and time and their units; give a body’s position with coordinates.
New words
space · fazotime · vaqtcoordinate · koordinatasecond · sekund
Explanation
All bodies are located in space, and motion takes place in time. Distances in space are measured in the unit of length, the metre (m); the SI unit of time is the second (s). To state a body’s position exactly we use a coordinate axis attached to the reference body: one axis (x) is enough for motion along a straight line, and two axes (x and y) are needed on a plane. Time is measured using a repeating process, such as the swing of a clock pendulum or the Earth’s rotation about its axis. The moment an event starts differs from its duration: “8:00” is a moment, “45 minutes” is a time interval.
Worked examples
A child standing 300 m from the school gate along a straight road has position x = 300 m (the gate is the origin).
If a lesson starts at 9:00 and ends at 9:45, its duration is 45 minutes = 45 · 60 = 2700 s.
Class activity
“Coordinates in class”: mark an x axis along a row of desks; pupils say the coordinate of their seat. Safety: do not run between desks.
Practice
1
What is the SI unit of time?
The second (s).
2
How many seconds are in 1 hour?
3600
3
How many coordinate axes are needed to give a position on a plane?
Two: x and y.
4
What is the difference between “14:00” and “2 hours”?
“14:00” is a moment of time, “2 hours” is a time interval (duration).