When an object changes velocity, it accelerates.
Acceleration is the change in velocity per second and is measured in m/s2.
Acceleration is a vector quantity because it has size and direction.
The relationship between acceleration, change in velocity and the time taken is given by the equation:
v = final velocity and u = initial velocity
If an object has an acceleration of 10 m/s2 it means that the velocity of the object changes by 10 m/s every second.
Find the acceleration of a car, if it starts at 10 m/s and it reaches 30 m/s in 4 seconds.
Final velocity v = 30 m/s.
Initial velocity u = 10 m/s.
The final velocity v – initial velocity u is 30 m/s – 10 m/s
= 20 m/s.
The acceleration is (final velocity v – initial velocity u) ÷ time, which is 20 m/s ÷ 4 s = 5 m/s2.
The acceleration of the car is 5 m/s2.
Find the acceleration of the car, if it starts at 20 m/s and slows down to 12 m/s in 2 seconds.
Final velocity v = 12 m/s.
Initial velocity u = 20 m/s.
The final velocity v – initial velocity u is 12 m/s – 20 m/s
= -8 m/s.
The acceleration is the (final velocity v – initial velocity u) ÷ time, which is -8 m/s ÷ 2 s = -4 m/s2.
The car has an acceleration of -4 m/s2.
A negative acceleration is called a retardation.
A minus sign means that the car is slowing down and has a retardation of 4 m/s2.