Distance, Displacement, Speed and Velocity
Distance is Scalar, Displacement is a Vector
- Distance is just how far an object has moved. It’s a scalar quantity, so it doesn’t involve direction.
- Displacement is a vector quantity. It measures the distance and direction in a straight line from an object’s starting point to its finishing point. The direction could be relative to a point, then 5m south, your displacement is 0m but the distance travelled is 10m
- If you walk 5m north, then 5m south, your displacement is 0m but the distance travelled is 10m
Speed and velocity are both how fast you’re going
Speed and velocity both measure how fast you’re going, but speed is a scalar and velocity is a vector
Speed is just how fast you’re going with no regard to the direction. Velocity is speed in a given direction
This means you can have objects travelling at a constant speed with a changing velocity. This happens when the object is changing direction whilst staying at the same speed. An object moving in a circle at a constant speed has a constantly changing velocity, as the direction is always changing
If you want to measure the speed of an object that’s moving with a constant speed, you should time how long it tales the object to travel a certain distance. You can then calculate the object’s speed from your measurements using this formula:
distance travelled= speed x time
Objects rarely travel at a constant speed. For these cases, the formula above gives the average speed during that time
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You need to know some typical everyday speeds
- Whilst every person, train, car is different, there is usually a typical speed that each object travels at. Remember these typical speeds for everyday objects
- Lots of different things can affect the speed something travels at. For example, the speed at which a person can walk, run or cycle depends on their fitness, their age, the distance travelled and the terrain as well as many other factors
- It’s not only the speed of objects that varies. The speed of sound changes depending on what the sound waves are travelling through, and the speed of wind is affected by many factors
- Wind speed can be affected by things like temperature, atmospheric pressure and if there are any large buildings or structures nearby
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