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Measurement of Time and Motion - SI unit of time

Grade 7CBSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Time is the interval between two events. In ancient times, people used natural events like sunrise, sunset, and moon phases to measure time.

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The standard unit of time in the International System of Units (SI) is the second, represented by the symbol ss.

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Larger units of time include minutes (minmin) and hours (hh). These are related as: 1 h=60 min1 \text{ h} = 60 \text{ min} and 1 min=60 s1 \text{ min} = 60 \text{ s}.

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A simple pendulum consists of a small metallic ball (bob) suspended from a rigid stand by a thread. The motion of a simple pendulum is an example of periodic or oscillatory motion.

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The time taken by the pendulum to complete one full oscillation is called its Time Period (TT).

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Modern timekeeping devices include quartz clocks, which use the vibrations of quartz crystals to measure time with high precision.

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The speed of an object is defined as the distance covered per unit time. Therefore, time can be calculated if distance and speed are known using the relation: t=dvt = \frac{d}{v}.

📐Formulae

1 minute=60 seconds1 \text{ minute} = 60 \text{ seconds}

1 hour=60 minutes=3600 seconds1 \text{ hour} = 60 \text{ minutes} = 3600 \text{ seconds}

Time Period (T)=Total Time TakenNumber of Oscillations\text{Time Period (T)} = \frac{\text{Total Time Taken}}{\text{Number of Oscillations}}

Time (t)=Distance (d)Speed (v)\text{Time (t)} = \frac{\text{Distance (d)}}{\text{Speed (v)}}

💡Examples

Problem 1:

A simple pendulum takes 32 s32 \text{ s} to complete 2020 oscillations. What is the time period of the pendulum?

Solution:

T=3220=1.6 sT = \frac{32}{20} = 1.6 \text{ s}

Explanation:

To find the time period, we divide the total time taken by the total number of oscillations. Here, 32 s32 \text{ s} divided by 2020 gives 1.6 s1.6 \text{ s}.

Problem 2:

If a car travels at a speed of 60 km/h60 \text{ km/h}, how many seconds will it take to cover a distance of 1 km1 \text{ km}?

Solution:

Time in hours=1 km60 km/h=160 hours\text{Time in hours} = \frac{1 \text{ km}}{60 \text{ km/h}} = \frac{1}{60} \text{ hours} Time in seconds=160×3600=60 s\text{Time in seconds} = \frac{1}{60} \times 3600 = 60 \text{ s}

Explanation:

First, we find the time in hours using Time=DistanceSpeed\text{Time} = \frac{\text{Distance}}{\text{Speed}}. Then, we convert hours to seconds by multiplying by 36003600 (since 1 h=3600 s1 \text{ h} = 3600 \text{ s}).

Problem 3:

Convert 22 hours and 1515 minutes into seconds.

Solution:

(2×3600) s+(15×60) s7200 s+900 s8100 s\begin{array}{r} (2 \times 3600) \text{ s} \\ + (15 \times 60) \text{ s} \\ \hline 7200 \text{ s} \\ + 900 \text{ s} \\ \hline 8100 \text{ s} \end{array}

Explanation:

First, convert the hours to seconds (2×3600=72002 \times 3600 = 7200). Next, convert the minutes to seconds (15×60=90015 \times 60 = 900). Finally, add both results together to get the total time in seconds.