CBSE Class 6 Science Chapter 10: Motion and Measurement of Distances NCERT Solutions

Solution: To understand how people and goods travel, we can categorize modes of transport based on the medium they use:

Land Transport: These are vehicles that travel on roads or tracks.

• Examples: Bus, Train, Car, Motorcycle, Bicycle.

Water Transport: These are vessels that move on bodies of water like rivers, lakes, and oceans.

• Examples: Boat, Ship, Submarine, Steamer.

Air Transport: These are vehicles that travel through the sky.

• Examples: Aeroplane, Helicopter, Hot Air Balloon.

Solution: Let's fill in the blanks with the correct terms and values:

1. One metre is 100 cm. (Since 1 m = 100 cm)
2. Five kilometre is 5000 m. (Since 1 km = 1000 m, so 5 km = 5 × 1000 m = 5000 m)
3. Motion of a child on a swing is periodic motion. (The child moves back and forth over a regular interval of time).
4. Motion of the needle of a sewing machine is periodic motion. (The needle moves up and down repeatedly in a regular pattern).
5. Motion of wheel of a bicycle is circular motion. (The wheel rotates around its center).

Solution: A pace or a footstep cannot be used as a standard unit of length because these measurements are not consistent. The length of a person's pace or footstep varies significantly from one individual to another. For example, an adult's pace is longer than a child's pace. This variability would lead to different measurements for the same distance depending on who is measuring, causing confusion and making it impossible to have a reliable, universally accepted measurement. Standard units, like the meter, are defined precisely and are the same for everyone, ensuring accuracy and consistency in measurements.

Solution: To arrange these lengths in increasing order, we need to understand their relative sizes. The standard relationships are:

• 1 kilometre (km) = 1000 metres (m)
• 1 metre (m) = 100 centimetres (cm)
• 1 centimetre (cm) = 10 millimetres (mm)

From these relationships, we can see that a millimetre is the smallest unit, followed by a centimeter, then a meter, and finally a kilometer is the largest unit among the given options. Therefore, arranging them in increasing magnitude gives: 1 millimetre, 1 centimetre, 1 metre, 1 kilometre.

Solution: We are given the height of a person as 1.65 meters and need to convert it into centimeters (cm) and millimeters (mm). We know the standard conversion factors:

• 1 metre = 100 centimetres
• 1 metre = 1000 millimetres

To convert 1.65 m to cm, we multiply by 100:

$$1.65\; \backslash text\{\; m\}\; =\; 1.65\; \backslash times\; 100\; \backslash text\{\; cm\}\; =\; 165\; \backslash text\{\; cm\}$$

To convert 1.65 m to mm, we multiply by 1000:

$$1.65\; \backslash text\{\; m\}\; =\; 1.65\; \backslash times\; 1000\; \backslash text\{\; mm\}\; =\; 1650\; \backslash text\{\; mm\}$$

So, the height of the person is 165 cm and 1650 mm.

Solution: The distance between Radha's home and school is given as 3250 meters (m). We need to express this distance in kilometers (km). We know the conversion factor between meters and kilometers:

$1\; \backslash text\{\; m\}\; =\; \backslash frac\{1\}\{1000\}\; \backslash text\{km\}$

To convert 3250 m to km, we divide the value in meters by 1000:

$$3250\; \backslash text\{\; m\}\; =\; \backslash frac\{3250\}\{1000\}\; \backslash text\{\; km\}\; =\; 3.25\; \backslash text\{\; km\}$$

Therefore, the distance between Radha's home and her school is 3.25 km.

Solution: To find the length of the knitting needle, we need to calculate the difference between the final reading and the initial reading on the measuring scale. The initial reading (one end) is 3.0 cm. The final reading (other end) is 33.1 cm. The length of the needle is the difference between these two readings:

$$\backslash text\{Length\; of\; needle\}\; =\; \backslash text\{Final\; reading\}\; -\; \backslash text\{Initial\; reading\}$$

$$\backslash text\{Length\; of\; needle\}\; =\; 33.1\; \backslash text\{\; cm\}\; -\; 3.0\; \backslash text\{\; cm\}\; =\; 30.1\; \backslash text\{\; cm\}$$

Thus, the length of the knitting needle is 30.1 cm.

Solution: Let's compare the motion of a bicycle and a ceiling fan:

Similarity:

• Both a bicycle (specifically its wheels) and a ceiling fan exhibit circular motion. The wheels of the bicycle rotate around their axles, and the blades of the ceiling fan rotate around the central motor.

Differences:

• Bicycle: When a bicycle is moving forward on a straight road, its overall motion is rectilinear motion (motion in a straight line). While the wheels are rotating (circular motion), the bicycle itself travels in a straight path.
• Ceiling Fan: A ceiling fan, when switched on, primarily exhibits rotational motion around a fixed axis (the motor). It does not typically show rectilinear motion unless the entire fan assembly is moving, which is not the usual case. The blades move in a circle, but the fan itself stays in one place.

Solution: An elastic measuring tape cannot be reliably used to measure distance because it is not a rigid object and can be stretched. Here are the problems you would encounter:

Why it cannot be used:

• Stretching: When you pull an elastic tape, it stretches. This stretching increases its length beyond its actual marked length. If you measure a distance using a stretched tape, the measured value will appear shorter than the actual distance.

Problems in telling someone about a measured distance:

• Inconsistent Measurements: You would not know how much the tape has stretched each time you use it. The amount of stretch can vary depending on how tightly you pull it, the temperature, or even the material's condition. This means repeated measurements of the same distance could yield different results.
• Lack of Standardization: Since the amount of stretch is variable and not standardized, the measurement taken with an elastic tape is not comparable to measurements taken with a standard, non-elastic tape or ruler.
• Difficulty in Communication: If you tell someone a distance measured with an elastic tape, they cannot verify it or use it accurately because they don't know the exact conditions under which it was measured (e.g., how much it was stretched). This makes communication of the measurement unreliable.

For accurate measurements, rigid measuring instruments like a non-elastic measuring tape, a ruler, or a meter scale are necessary.