Motion - Scalars and Vectors
Everything is in motion one way or another, even if your still right now the tiny particles bouncing around inside you are constantly moving. Movement is needed for our everyday survival such as eating, breathing, allowing the earth to rotate so we don't freeze or burn depending on what side we're on! Anyway since movement is so common and so good for us we need to know more about it so we can find some answers about how it works and why!
Physics is very mathematical, this is because scientists look at some pretty small and invisible things that would be too complex or impossible to experiment on! So movement or motion of objects has names and rules scientists need to follow. By names I don't mean 'going fast' or 'stopping', I mean the proper smart names such as acceleration and velocity!
Scientists like to group similar characteristics so that they can easily see what does what. The two main groups for speed are;
Scalars - Quantities that describes just the numerical value of the speed
Vectors - Quantities that describe the numerical value of the speed but also the direction the speed is going.
These groups are the key to figuring out how to calculate any hypothesis to do with speed and what the outcome should look like.
Distance and Displacement are two examples of where scalar and vector types come into play.
Distance is a typical term that most non-physicists know and it's as simple as how far an object has gone from its starting position.
Displacement, however, is a bit more interesting as it is how far out of place an object has gone. This adds direction so we can safely assume this is going to use the vector quantity.
Say, for example, a cat ran up a 6-meter tree and then ran down it again to its original position. For the distance quantity, the cat has gone 12 meters in total as its got up and down the 6-meter tree. However, in 'displacement' the vector quantity is zero because it has to factor in the direction so the 6 meters up the tree is canceled by the cat then running back down the tree so zero 'displacement' has occurred.
Another big example is speed and velocity. Speed is a scalar quantity because is refers to how fast an object is moving. Velocity, however, is a vector quantity because it refers to the rate an object changes position. This relates to the cat scenario because if a person is pacing back and forth rapidly but always returning to their original position then their velocity will always be 0 because velocity is the measure of the rate an object changes position.
Determining the direction of the velocity vector is very simple as it is just the same direction that the object is moving, so if it was moving up the velocity would be up and if it was moving east the velocity would be east etc.
To calculate the average speed of an object you would use the formula;
Average speed = Distance travelled/ Time
To calculate the average velocity of an object you would use the formula;
Average velocity = displacement / time
However, there is one other type of speed that some may get confused about. Instantaneous speed.
Average speed is the measurement of the overall speed during a particular time, the instantaneous speed is the speed at any given time.
For example, if you looked at the speedometer in a car while moving it would show the current speed which would be the instantaneous speed. So to get the average speed you would have to average all the readings taken on the speedometer.