Acceleration, velocity and displacement are the physical quantities often used to describe the motion of objects. These quantities are also known as the quantities of kinematics.
What are acceleration? Acceleration is a derived vector quantity that describes the motion of any object in terms of change in velocity per unit time. To be specific, it describes the increase in velocity of an object in one second.
Ex: The car is moving with a constant acceleration of 4ms-2. This means that the velocity of the car increases 4ms-1 every 1s. This occurs constantly throughout the motion of the car.
What is meant by velocity? Velocity is a derived vector quantity that describes the motion of any object in terms of change in displacement per unit time.
Constant velocity means the velocity is fixed throughout the motion. It also means the displacement covered by object is constant every one second.
The trolley above is moving down an inclined plane at the constant velocity of 1ms-1. This means that as the trolley is moving down the inclined plane, it covers a displacement of 1m every 1s. If the inclined plane is 3m long, it will take the trolley 3s to reach the bottom.
What is displacement? Displacement is a straight line distance measured from the initial point (reference point) to the final point.
Constant displacement is another way of saying that the object is stationary. When a displacement is constant, it means the final position is not changed. Hence, the object is resting at the final position.
Zero displacement is achieved when the final position meets the initial position. Hence, there is no distance between the final and initial positions.