Speed vs Velocity

Speed is a scalar quantity, whereas velocity is a vector quantity.

Speed is distance over time. Speed is a scalar quantity that refers to how fast an object is moving.” Speed is the rate at which an object covers distance. A fast-moving object is said to have a high speed i.e. it covers a large distance in a short amount of time. Whereas, a slow-moving object that has a low speed covers a small distance in the same amount of time. An object with no movement at all has a zero speed.

Average speed = Distance traveled / Time taken = s/t

Velocity is displacement over time. Velocity is a vector quantity that refers to “the rate at which an object changes its position.” If a person keeps on moving two steps forward and then two steps back, they return to the same position. Even though the person might move very fast, it would result in a zero velocity.

This is because the person always returns to the original position. Since velocity is defined as the rate at which the position changes, two steps forward and then two steps back results in zero velocity. For someone to maximize their velocity, they have to keep on moving away from their initial point. Every step must go into moving that person further from where he or she started.

Velocity is a vector quantity. When evaluating the velocity of an object, one must keep track of direction. It would not be enough to say that an object has a velocity of 49 mi/hr.

One must include direction information in order to fully describe the velocity of the object. For instance, you must describe an object’s velocity as being 49 mi/hr, west. This is one of the essential differences between speed and velocity.

Velocity = displacement / time taken = (Xf – Xi) / t

Practice Problems

1. What is the average speed of a cheetah traveling 100m in 4 seconds?

Distance traveled: 100 m

Time taken = 4 sec

Average speed = 100 meter /4 sec = 25 m/s

2. Jones travels 12 km to the east. He turns the car around and travels 2 km to the west. What is his Average velocity if the time taken is 0.5 hours?

Displacement = Xf – Xi = 12 – 2 = 10 km → 10,000 m

Time taken = 0.5 hrs → 1800 sec

Average velocity = 10000 meter / 1800 sec = 5.55 m/s

3. The length of a circular track is 1000m. An Olympic runner can run the entire track in 6 minutes. What is her Average velocity?

Displacement = 0 m (since the final position and initial position are the same, the displacement is zero. Do not confuse displacement with distance traveled, which would be 1000 m).

Since displacement is zero, velocity would be zero by default.