# Acceleration and velocity

## Main Question or Discussion Point

Hi,

Velocity is defined as speed in a given direction and acceleration is the rate at which velocity changes over time.

Lets say a car is being driven on a road. If the speed changes, then the car is accelerating. Am I able to say that if direction changes, then the car has also accelerated?

Thanks,

Related Classical Physics News on Phys.org
cepheid
Staff Emeritus
Gold Member
Hi,

Velocity is defined as speed in a given direction and acceleration is the rate at which velocity changes over time.

Lets say a car is being driven on a road. If the speed changes, then the car is accelerating. Am I able to say that if direction changes, then the car has also accelerated?

Thanks,
Yes.

If the velocity vector is changing, there is an acceleration.

Example: uniform circular motion. For an object moving in a circle at a constant speed, there is a "centripetal" acceleration (an acceleration that points towards the centre of the circle). Since the acceleration is radially inward, whereas the velocity is always tangent to the circle, these two vectors are always perpendicular to each other. For this reason, the acceleration doesn't increase the magnitude of the velocity vector. All it does is rotate the velocity vector.