Class 9 Science

Motion

  • Rectilinear motion
  • Distance and displacement

Motion: If an object changes its position with respect to a reference point with elapse of time, the object is said to be in motion.

Rest: When an object does not change its position with respect to a reference point with elapse of time, the object is said to be in rest.

Example: When a vehicle changes its position with respect to an electric pole (a reference point) with elapse of time, then vehicle is called in motion. And if the same vehicle does not change its position with respect to that electric pole, the vehicle is called in the state of rest.

Thus to observe the motion of any object; two things are necessary – a reference point and time.

In the above example; vehicle is the object and electric pole is the reference point. A building, tree, or any other static thing can be taken as reference point to observe the motion of an object.

Motion along a straight line:

When an object moves along a straight line, the motion of the object is called rectilinear motion. For example; motion of a vehicle along a straight road.

Distance and Displacement:

Distance is the length of path covered by a moving object in the given time irrespective of direction. Distance has only magnitude and no direction.

SI unit of distance is meter (m).

Kilometer is used to measure bigger distance and it is abbreviated as ‘km’.

Displacement is the shortest possible distance covered by a moving object from initial point in a particular direction. In other words, shortest distance between initial point and final point is called the displacement.

Displacement has both magnitude and direction while distance has only magnitude.

Suppose, a ball is rolling along a straight line.

motion in straight line

Case 1:

Suppose, the ball starts moving from point A and reaches at point B.
Thus, distance covered by ball = 10 m
Displacement of ball = 10 m towards west.

Case 2:

Suppose, ball starts moving from point A and reaches to B. Again it returns on the same path from point B and reaches at A.

Thus, distance covered by the ball = distance from A to B + Distance from B to A
= 10 m + 10 m = 20 m
In this condition, distance covered by ball = 20 m.
Since, ball returns at point A, thus displacement of the ball = 0

Case 3:

Suppose, the ball starts moving from point A, reaches point B and returns back to point C.

Then, the distance covered by ball = distance from A to B + Distance from B to C
= 10 m + 7 m = 17 m
Displacement of ball = Distance of point C from A = 3 m towards west.

Quiz



See Answer

1: (c) Both a and b, 2: (a) Magnitude, 3: (b) Car on straight road, 4: (d) Pendulum, 5: (c) Butterfly, 6: (a) Speed, 7: (b) Meter, 8: (d) Meter per second, 9: (c) Meter per second2, 10: (a) First equation of motion


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Elements and compounds are pure substances. All other substances are mixtures which means they are not pure substances.

Atoms and Molecules

Read about law of conservation of mass, law of constant proportions and Dalton's atomic theory.

Structure of Atoms

Atom is made of three particles; electron, proton and neutron. These particles are called fundamental particles of an atom or sub atomic particles.

Cell: The Fundamental Unit of Life

A cell is capable of independent existence and can carry out all the functions which are necessary for a living being.

Tissue

A groups of cells which is meant for a specific task is called tissue. Tissues are the first step towards division of labour in complex organisms.

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Without proper classification, it would be impossible to study millions of organisms which exist on this earth.

Motion

If an object changes its position with respect to a reference point with elapse of time, the object is said to be in motion.

Force & Laws of Motion

Force has numerous effects. Force can set a stationary body in motion. Force can stop a moving body.

Gravitation

Earth attracts everything towards it by an unseen force of attraction. This force of attraction is known as gravitation or gravitation pull.

Work & Energy

When force is exerted on an object and object is displaced, work is said to be done. It means work is the product of force and displacement.

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Sound is a type of energy. Sound travels in the form of wave from one place to another.

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Food security is said to exist when all people, at all times, have physical and economic access to sufficient, safe and nutritious food to meet their dietary needs and food preferences for an active and healthy life.