Important Terms

A body is said to be at rest if it does not change its position concerning its surroundings.

A body is said to be in motion if it changes its position concerning its surroundings.

Physical quantities which are described by their magnitude only are known as scalars. 

Physical quantities which are described by their magnitude and direction are known as vectors.

Position means the location of a certain place or object from a reference point.

The distance traveled in any direction by a boy in unit time is called speed.

If the speed of a body does not change with time then its speed is uniform.

Average speed of a body is the ratio of the total distance covered to the total time taken

We define velocity as the rate of change of displacement or speed in a specific direction.

The average velocity of a body is defined as the ratio of its net displacement to the total time.

If a body covers equal displacements in equal intervals of time, however small the interval may be, then its velocity is said to be uniform.

The rate of change of velocity of a body is called acceleration.

A body has uniform acceleration if it has equal chances in its velocity in equal intervals of time, however small the interval may be.

The graph is a pictorial way of describing information as to how various quantities are related to each other.

Distance-time graphs provide useful information about the motion of an object. The slope of the displacement-time graph gives the velocity of the body.

Speed-time graph is also useful for studying motion along a straight line.

The distance traveled by a body can also be found from the area under the the Velocity-time graph if the motion is along a straight line.

When a boy is dropped freely he falls with an acceleration towards the earth. This acceleration is called acceleration due to gravity and is denoted by g. the numerical value of g is approximately 10 ms^-2 near the surface of the Earth.