Class 9 Science

Chapters

# Distance Time Graph

• Calculation of velocity using distance time graph
• Distance time graph of a body in accelerated motion

When an object is moving with uniform velocity, the slope of graph is always a straight line. In other words slope of straight line of a distance-time graph shows that object is moving with uniform velocity.

In the above graph, straight slope line shows that object is moving with uniform velocity. Slope OB shows the velocity of the object.

## Calculation of Velocity using distance-time graph:

To calculate the velocity, let take two points A and B on the slope OB.

Draw one line parallel to y-axis and another parallel to x-axis from B.

Again draw a line parallel to y-axis and another parallel to x-axis from point A.

Let, line parallel to x-axis from point B cut at a point, S2 at y-axis.

Line parallel to x-axis from point A cut at point, S1 at y-axis.

Let, line parallel to y-axis from point B cut at t2 at x-axis.

Line parallel to y-axis from point A cut at t1 at x-axis.

Now, BC= Distance = S2 – S1 and AC = time = t2 – t1

We know that slope of the graph is given by the ratio of change in y-axis and change in X-axis.

Or, Slope = (text{Change in y-axis})/(text{Change in x-axis})

Thus, slope, AB=(BC)/(AC)

Or, v=(s_2-s_1)/(t_2-t_1)

Where, v= velocity, (s_2-s_1) = interval of distance and (t_2-t_1) = time interval

Thus, text{velocity}=text{Distance}/text{Time}`

## Distance – Time Graph of a body moving with Accelerated motion:

When graph of distance Vs time is plotted for an object moving with accelerated motion, i.e. with increasing non-uniform speed, the slope of graph will not be a straight line. The rising trend of slope shows the increasing trend of velocity.

## Matter in Our Surroundings

Anything that has both mass and volume is called matter. You can also say that anything which has mass and which occupies space is called matter.

## Is Matter Around Us Pure?

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.

## Diversity in Living Organisms

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.

## Sound

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

## Why Do We Fall Ill

Health is a state of physical, mental and social well being. A condition in which the affected person is unable to carry out normal activities is termed as disease.

## Natural Resources

Resources which are obtained from nature are called natural resources. Examples: Air, water, soil, wood, etc.

## Improvement in Food Production

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.