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Motion and Measurement of Distances - Describing Position

Grade 6CBSE

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

🔑Concepts

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To describe the position of an object, we need to specify a fixed point of reference, which is called the Reference Point or Origin.

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A complete description of position involves three components: the distance from the reference point, the direction from the reference point, and the name of the reference point itself.

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Distance is the measure of how far an object is from a reference point or how much ground an object has covered during its motion.

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For accurate measurement of position and distance, the International System of Units (SI) is used globally. The standard unit of length is the meter (mm).

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When measuring distance with a scale, the eye must be positioned exactly vertically above the point of measurement to avoid parallax error.

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If the '0' mark of a measuring scale is broken or obscured, the measurement can be taken from any other full mark (e.g., 1 cm1 \text{ cm}), and that initial reading must be subtracted from the final reading.

📐Formulae

1 km=1000 m1 \text{ km} = 1000 \text{ m}

1 m=100 cm1 \text{ m} = 100 \text{ cm}

1 cm=10 mm1 \text{ cm} = 10 \text{ mm}

Correct Length=Final Reading−Initial Reading\text{Correct Length} = \text{Final Reading} - \text{Initial Reading}

💡Examples

Problem 1:

While measuring the length of a pencil, the reading of the scale at one end is 3.0 cm3.0 \text{ cm} and at the other end is 14.7 cm14.7 \text{ cm}. What is the length of the pencil?

Solution:

Length of the pencil = 14.7 cm−3.0 cm=11.7 cm14.7 \text{ cm} - 3.0 \text{ cm} = 11.7 \text{ cm}

Explanation:

To find the actual length when the scale does not start from zero, we subtract the starting point reading from the ending point reading.

Problem 2:

Rohan's house is 2500 m2500 \text{ m} away from his school. Express this distance in kilometers (kmkm).

Solution:

Since 1000 m=1 km1000 \text{ m} = 1 \text{ km}, we divide the distance by 10001000: 25001000 km=2.5 km\frac{2500}{1000} \text{ km} = 2.5 \text{ km}

Explanation:

To convert meters to kilometers, the numerical value is divided by 10001000 because a kilometer is a larger unit.

Problem 3:

An athlete runs 450 m450 \text{ m} forward from the starting line and then walks 125 m125 \text{ m} back towards the starting line. Use vertical subtraction to find his current distance from the starting line.

Solution:

450−125325\begin{array}{r} 450 \\ - 125 \\ \hline 325 \end{array} The distance is 325 m325 \text{ m}.

Explanation:

The current position (distance from origin) is calculated by subtracting the distance moved backwards from the total distance moved forward.