People often use the words velocity and speed as though they mean the same thing in how fast an object is moving.
However, in the world of physics and science, the two words don’t mean the same thing at all.
Speed may be how vast something is moving, but the term ‘velocity’ refers to how fast an object is moving ‘in a particular direction’.
Physicists refer to speed as a SCALAR, which actually means it’s a quantity that has only size or magnitude.
- Velocity is referred to as a VECTOR, which actually means that it has both direction and magnitude.
- An example of the difference would be to announce that there is a car that is going 50 miles per hour. That is announcing its speed. But if you said the same car was moving north at 50 miles per hour that is announcing its velocity.
The term ‘relative velocity’ is a term that is used to relate the difference in measurement of speed in relation to a reference point.
An example might be the experience you get when the car next to you is moving and you think it is your car. Your car hasn’t moved but it is the visual experience of the reference point that makes you think it has.
Another example of relative velocity is when you are in a slow-moving train going in the same direction as a fast-moving train. When the fast-moving train passes you it doesn’t seem to be going all that fast. But if you were standing outside at the station you would think the fast-moving train was going much faster. Each of these examples relies on a ‘reference point’ for velocity.
If you look at yet another example of velocity and consider a ship that is moving along the ocean at fifteen knots (one nautical mile per hour equals one knot). When someone on the shore looks at the ship they may see a passenger, sitting on the deck and that person will also be moving at fifteen knots.
If, however, the passenger gets up and begins to walk across the ship in the same direction the ship is going, at three knots, the person on the shore will think they are moving at 18 knots (15+3). The same types of changes happen if the passenger moves diagonally or even going backward. The person on the shore sees the passenger moving at a different velocity than the ship.
Speed is configured in units and, depending upon the area of the world or the type of transportation, they can be miles per hour, kilometers per hour or knots. In science, however, they are listed as ‘meters per second’ (m/s) or kilometers per hour (km/h). Other speed units can include kilometers per second (km/s) or even meters per minute (m/min).
Distances and Units of time that are used in measurements:
1 hour (1 h) = 60 minutes (60 min) = 3,600 seconds (3,600 s)
1 minute (1 min) = 60 seconds (60 s)
1 second (1 s) = 1/60 of a minute = 1/3600 of an hour
1 kilometer (1 km) is equal to 1,000 meters
1 meter (1 m) = 1/1000 of a kilometer
1 meter (1 m) is equal to 100 centimeters (100 cm)
1 cm = 1/100 of a meter