Definition and real life examples of velocity

Velocity is not exactly the same as speed. Keep reading to see the difference between the two.

The speed is just how fast a car is moving without taking into consideration its direction. If you are looking at the speedometer and you see 50 m/h, this is just the speed of the car that you are driving.

However, you must have both speed and direction in order to have velocity. 

  • If an airplane travels 200 miles per hour, we are talking about its speed.
  • If an airplane travels 200 miles per hour to the east, we are talking about its velocity.

Definition of constant velocity 

A velocity is constant if the following two conditions are met.

  • The speed is constant
  •  The direction is constant 

Constant speed means that the object is moving at the same speed or does not go faster or slower.

Constant direction means that the path is a straight line.

It may make sense to you why the object should not move faster or slower in order to have constant speed.

It might not make sense why the path should be a straight line.

Simply put, if the path is not a straight, the direction will change.

For example, because the path is not completely straight, the green dot below changes direction 2 times.

The first time the direction changes is on the blue line and the second time is on the black line.

Change of direction

The same thing will happen if the path is a circle. The direction will change constantly. 

In circular motion, the direction keeps changing

You can see from the figure above that the green dot changed direction 3 times.

Any object moving on a circular path will never have a constant velocity because the direction of the object changes every instant. However, the object may have constant speed. 

Notice that from the definition of velocity, you can see that a velocity is changing whenever the speed, the direction, or both are changing.

Again, even if an object moves at constant speed around a curved path, it does not move at constant velocity. 

When you are looking at your speedometer and you see 65 miles per hour and your car is in cruise control, you are seeing constant speed.

You are not seeing velocity since the speedometer does not know your direction.

Some cars are equipped with a compass. If you combine your speedometer with the reading on the compass, then you will have constant velocity if you are on cruise control and you are heading straight in the same direction.

Velocity quiz

This velocity quiz will test your knowledge of speed and velocity. After completing this quiz, you should be able to clearly see the difference between speed and velocity. You will not need to use a paper and pencil to complete this quiz.

My recommendation is to first read this lesson about the definition of velocity and then take this quiz without using a calculator.

Objective of the quiz:

  • Master the meaning of speed.
  • Master the meaning of velocity.
  • Master the difference between speed and velocity.
  • Master the meaning of constant speed.
  • Master the meaning of constant velocity. 
  • Master the meaning of speed, velocity, constant speed, constant and velocity with concrete, real life examples. 

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