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When an object is moving at a steady speed, the speed can be found if the distance travelled and the time taken to travel it are known. Speed is a scalar quantity, since it is given by its magnitude only.
When describing speed for walking, running and cycling, the speeds will vary due to many factors, such as age, fitness level and the total distance travelled, however some typical values for this and for some transportation methods are shown in the given table. The typical speed of sound in air is approximately 340 m/s, whereas in a vacuum it is 0 m/s. This is because there are no particles present, which are needed to propagate sound waves, therefore they do not travel in a vacuum
The equation used to calculate the steady speed of a moving object can also be used to calculate the speed of objects moving at a non-steady speed. The resultant speed is called the average speed and is calculated using the total distance travelled and the time within which it is travelled. For an object not moving at a steady speed, the instantaneous speed cannot be known, since the speed will be different at any point in time during its journey.
A distance-time graph can be drawn to model the motion of an object moving in a straight line. The gradient of a distance-time graph represents the speed of the object, thus the greater the slope of the graph, the greater the speed of the object.
The gradient of a distance-time graph represents the speed of the object whose motion it describes. For objects travelling at a constant speed, this can be calculated using a triangle, whereas for acelerating objects, a tangent can be drawn at the point for which the speed is wanted and the triangle for the tangent line can be used to calculate the speed.
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