WHAT IS VELOCITY?
Average velocity is the displacement divided by the total time to travel. Displacement is the straight-line distance between the starting position and the final position, with direction toward the final position. It is a vector quantity. For straight-line motion in one direction, speed and velocity are very similar. Their magnitudes are the same, and they all travel straight in the same direction. The only difference would be that velocity must be written with the direction, since it is a vector quantity.
There is also instantaneous velocity. Which means the velocity at any very instant of time. The instantaneous speed that you find on a car's speedometer, add a direction to it, then you have an instantaneous velocity for that car at that very instant of time. But however, the car's direction changes very often, then the motion is an accelerated motion.
If the velocity is uniform, or constant, then we don't need to worry about changes. Think of an airplane is flying at a constant speed of 320 kilometers per hour westward at without changing it's attitude. Then the plane is traveling at a constant velocity and fly in a straight line. Therefore, you can say that the instantaneous velocity and average velocity are the same.
The earth is travelling at a speed of 66,700 miles per hour. Does that mean we are travelling at that speed too? The answer is yes, relative to the sun, we are travelling that fast. The earth is travelling at a constant speed, however, not a constant velocity, since it's travelling in a circular motion, which means that direction changes all the time. We don't sense this great speed because of the small relative motion of the stars.
If you are blind-folded sitting in a smooth driving quiet car. You won't be able to tell if you are travelling. Unless the car speeds up, slows down, or changing direction. A change of velocity, or can also think of a change in speed or direction of an object, is called acceleration.
[Introduction] [Straight-Line Motion] [Speed] [Velocity] [Acceleration] [Circular Motion]
[Satellites] [Force] [Gravitation] [Inertia] [Newton's Law] [Momentum] [Mass and Weight]
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