Measurement of Time and Motion
How do we measure time, and how fast is something moving? This Class 7 Curiosity chapter looks at the measurement of time, the different types of motion, the idea of speed as distance divided by time, the simple pendulum, and how a distance–time graph pictures motion.
Learning objectives
- Describe how time is measured.
- Identify types of motion.
- Calculate speed as distance ÷ time.
- Read a simple distance–time graph.
Key concepts
Measuring time
Time is measured in seconds, minutes and hours, with the second as the basic unit. Early people used the Sun and repeating events; today we use clocks and watches. Any regularly repeating motion can measure time, which is why a swinging pendulum was historically used in clocks.
Types of motion
An object is in motion if its position changes with time. Motion can be along a straight line (rectilinear), back and forth (oscillatory, like a swing), round and round (circular, like a fan blade), or repeating after fixed intervals (periodic). Recognising the type helps describe how things move.
Speed
Speed tells us how fast an object moves and is the distance travelled divided by the time taken: speed = distance ÷ time. Its common unit is metres per second (m/s) or kilometres per hour (km/h). A higher speed means more distance covered in the same time.
Uniform motion, pendulum and graphs
Motion is uniform when equal distances are covered in equal time intervals, and non-uniform when the speed changes. A simple pendulum takes the same time for each swing, making it a good timekeeper. A distance–time graph shows distance on one axis and time on the other; a straight slanting line means uniform motion.
Important formulas
Speed
speed = distance ÷ time
Distance
distance = speed × time
Key definitions
- Motion
- A change in the position of an object with time.
- Speed
- The distance travelled in unit time (distance ÷ time).
- Uniform motion
- Motion covering equal distances in equal time intervals.
- Oscillation
- One complete to-and-fro movement, as of a pendulum.
Solved examples
Q1. A car travels 100 km in 2 hours. Find its speed.
Solution: Speed = 100 ÷ 2 = 50 km/h.
Q2. What is the basic unit of time?
Solution: The second.
Q3. What kind of motion does a swing show?
Solution: Oscillatory (to-and-fro) motion.
Common mistakes to avoid
- Dividing time by distance instead of distance by time for speed.
- Forgetting to keep units consistent (km with hours, m with seconds).
- Confusing uniform with non-uniform motion.
- Thinking a curved distance–time graph means uniform motion.
Measurement of Time and Motion — MCQ Quiz
10 questions with instant feedback. Use number keys 1–4 to answer.
The basic unit of time is the:
Practice questions
Short answer
Write the formula for speed.
Speed = distance ÷ time.
What is uniform motion?
Motion covering equal distances in equal intervals of time.
Why is a pendulum useful in clocks?
Because each swing takes the same time, so it keeps regular time.
Long answer
Explain speed and the difference between uniform and non-uniform motion, with examples.
Speed measures how fast an object moves and is found by dividing the distance travelled by the time taken: speed = distance ÷ time, measured in units like m/s or km/h. Motion is described as uniform when the object covers equal distances in equal intervals of time, so its speed stays the same — for example, a car moving steadily at 50 km/h. Motion is non-uniform when the speed changes from moment to moment, such as a bus speeding up and slowing down in city traffic. On a distance–time graph, uniform motion appears as a straight slanting line, while non-uniform motion gives a curved line.
How is time measured, and how does a simple pendulum help?
Time is measured in units of seconds, minutes and hours, with the second as the basic unit. Since any regularly repeating event can be used to mark time, people have measured time using the Sun, sand timers and water clocks in the past. A simple pendulum — a small weight hanging from a fixed point — is especially useful because each complete to-and-fro swing, called an oscillation, takes the same amount of time. This steady, repeating motion allowed pendulums to be used in clocks to keep accurate time, illustrating the link between regular motion and the measurement of time.
HOTS (Higher Order Thinking)
Two cars cover the same distance, but one takes less time. Which is faster, and why?
The one taking less time, because for the same distance a shorter time means a higher speed (distance ÷ time).
If a pendulum's swing always takes the same time, what happens to the number of swings in one minute if you do not change the pendulum?
It stays the same, since each swing takes a fixed time — that constancy is what makes it a good timekeeper.
Quick revision
Revision notes
- Time unit: second; any regular repetition can measure time.
- Motion = change of position with time; types: straight, circular, oscillatory, periodic.
- Speed = distance ÷ time (m/s or km/h).
- Uniform motion = equal distance in equal time = straight line on a distance–time graph.
Key takeaways
- Speed = distance ÷ time.
- Uniform motion keeps a steady speed.
- A pendulum's regular swing measures time.
Frequently asked questions
How do I calculate speed?
Divide the distance travelled by the time taken.
What is an oscillation?
One complete to-and-fro movement, as of a pendulum.
What does a straight line on a distance–time graph mean?
The object is in uniform motion (constant speed).