Velocity

Speed does not refer to the moving direction of the object. The term velocity isused to indicate both the direction and the magnitude of the object.The velocity of an object could be represented by using the
following equation.

The SI unit for velocity is metres per second (m s-1)Velocity is the displacement per unit time or is the rate of change of displacement.Since displacement has a direction, the direction of velocity is also in similar to
that of the displacement. That means, velocity has a magnitude and a direction.Therefore, velocity is a vector quantity.
Refer to the diagram given in Fig           
3.1.3. It shows two vehicles with the
velocities of 40 km h-1 travelling in the
opposite directions.
Are the two velocities same?
clarify your answer.
Though the magnitudes of the two velocities are same, the directions are
different. Therefore, the velocities are not equal to each other.
Acceleration and deceleration
According to the experience of travelling by vehicles we know that the speed of a vehicle changes from time to time. The driver can increase the speed by pressing onthe accelerator and he can decrease the speed by using the brakes.When a vehicle starts and drive ahead, its speed will increase. It is called 'Acceleration'.
Acceleration
The following table shows the change of velocity of a train which started its motion from rest, with time

 Note that in the above example,
• The train starts from rest.
• Velocity has increased uniformly.
• Every second, the velocity has increased by 3 m s-1
.
Thus, the object has accelerated at 3 metres per second in every second.Acceleration of an object could be represented by the following equation.

SI unit for acceleration is metres per square second (m s-2)
Acceleration is defined as the change of velocity per unit time or as the
rate of change of velocity. Acceleration is a vector quantity.
When a driver presses the accelerator, the velocity of the vehicle is increased as well. When a car drives away from the traffic lights, its velocity gradually increases.Then it is said that the vehicle is accelerating.Refer to the velocity between 2nd and 5th seconds in the table 3.1.1












Deceleration
What happens when you apply brakes on a moving vehicle. The vehicle will slow down. This is the opposite of acceleration. It is known as deceleration.
e. g. The speedometer of a vehicle indicates 54 km h-1 at point A. After
applying brakes it arrives at point B at a speed of 36 km h-1 in 4 seconds. Assume that the velocity has decreased uniformly.