A Cautionary NoteДЄverage speed is often derived from units of distance or time that must convert to other units for the final answer. You might have to make numerous stops when walking a dog, but in all three cases, you can easily calculate average speed by dividing the total distance traveled by total elapsed time. That three-toed sloth may have stopped for a moment to catch its breath before hurrying onward. The porpoise could have started slowly, sped up, paused to play, and continued. If you need the total distance, you must have the speed and the time:ДЄverage speed is especially useful because it takes into account the reality of an event, rather than assuming something or someone is moving at a constant speed. You plug those two scalar quantities into their parts of the triangle to get: If you need the total time, you must have the distance and speed. If you know two of the three variables, distance, time, and speed, then you can use algebra to find what you're missing. S = 89.7 k m 3 h o u r s = 29.9 k i l o m e t e r s p e r h o u r ( k p h ) Plug those two given numbers into the triangle in their two corners to get: You are told that it can move a distance of 89.7 k i l o m e t e r s in 3 h o u r s. Say you want to find the average speed of a Pacific Bottlenose porpoise.

To get distance, D, multiply speed times the amount of time: s Г— t.

To get elapsed time, t, divide total distance by speed: D s.

To get average speed, s, divide total distance by elapsed time: D t.

The three parts in the triangle are set up in their correct positions mathematically: The distance/speed/time triangle is handy for calculating this and two other scalar quantities (distance and time): To calculate the average speed of an object, you must know the total distance an object travels and the total elapsed time of its whole journey.

Distance and time are also scalar quantities and can also be measured with numbers. Average and instantaneous speeds are always scalar quantities, which means you can always measure them with a number. Speed, being a scalar quantity, can never be less than 0. Scalar quantities can go from 0 (no speed) to infinitely fast.ДЄ vector quantity has size and direction, as with the movement of an airplane in the sky. It only has a size, meaning a magnitude or scale. Finding the average speed is far easier вЂ“ and usually far more useful вЂ“ than calculating instantaneous speed.

Instantaneous speeds fluctuate throughout a timed event. In most cases you do not need to know the formula for instantaneous speed, v, finding the limit as the change in time (the вЂњinstantвЂќ) approaches 0: To simplify measurements and make progress on a physics or mathematics problem, you take the average speed of all the discrete events, saying the car traveled 5.5 m i l e s in 6 m i n u t e s:ДЄll those other measurements, at particular moments in the journey, are instantaneous speeds. It might be 0 mph, then 7 mph in another instant, then 53 mph, then 61 mph, and finally 3 mph before returning to 0 mph. At any given moment, the car is not traveling at 55 m i l e s p e r h o u r ( m p h ). Instantaneous SpeedДЄverage speed takes into account the entirety of an event, such as a car accelerating from a stop, speeding up, traveling for a while, then slowing at a yellow light, and finally stopping.ДЄ car travels at different speeds. A v e r a g e S p e e d ( s ) = t o t a l d i s t a n c e t o t a l e l a p s e d t i m eДЄverage speed contrasts with instantaneous speed.

Average speed symbol