CBSE Class 9 Science Motion Notes

CBSE Class 9 Science Motion Notes. There are many more useful educational material which the students can download in pdf format and use them for studies. Study material like concept maps, important and sure shot question banks, quick to learn flash cards, flow charts, mind maps, teacher notes, important formulas, past examinations question bank, important concepts taught by teachers. Students can download these useful educational material free and use them to get better marks in examinations.  Also refer to other worksheets for the same chapter and other subjects too. Use them for better understanding of the subjects.

MOTION

Motion means movement. The motion of an object is perceived when its position changes continuously with respect to some stationary object.

DISTANCE

The distance travelled by an object is the length of actual path travelled by the object during the motion.

DISPLACEMENT

The displacement of an object is the shortest distance travelled between the initial and final position of the object.

* When final position coincides with the initial position, displacement is 0 but distance is not equal to 0.

* Both, the distance and displacement are measure in meter or cm or km.

* Distance is a scalar quantity having only. Displacement is a vector quantity having both magnitude and direction.

* The distance travelled by an object in motion can never be zero or negative. The displacement can be positive, zero or negative.

INTEXT QUESTIONS 

1. A farmer moves along the boundary of a square field of side 10 m in 40 s. What will be the magnitude of displacement of the farmer at the end of 2 minutes 20 seconds?

Ans. The farmer takes 40 s to cover 4 × 10 = 40 m. In 2 min and 20 s (140 s), he will cover a distance = 40/40Χ140 m Therefore, the farmer completes 140/40= 3.5  rounds (3 complete rounds and a half round) of the field in 2 min and 20 s.

That means, after 2 min 20 s, the farmer will be at the opposite end of the starting point.

Now, there can be two extreme cases.

Case I: Starting point is a corner point of the field. In this case, the farmer will be at the diagonally opposite corner of the field after 2 min 20 s.

Therefore, the displacement will be equal to the diagonal of the field.

Hence, the displacement will be √10² +10² =14.1m

Case II: Starting point is the middle point of any side of the field. In this case the farmer will be at the middle point of the opposite side of the field after 2 min 20 s. Therefore, the displacement will be equal to the side of the field, i.e., 10 m. For any other starting point, the displacement will be between 14.1 m and 10 m.

2. Which of the following is true for displacement?

(a) It cannot be zero.

(b) Its magnitude is greater than the distance travelled by the object.

Ans. (a) Not true. Displacement can become zero when the initial and final position of the object is the same.

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