How does size of an object affects its speed? Suppose if two objects of different sizes (very different indeed) moves at speed of say 100 mph for an hour, will the object greater in size covers the distance in lesser time or the same time? Why?

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    $\begingroup$ Can you clarify why you think size would affect the distance covered? $\endgroup$ – pfnuesel Jul 27 '15 at 10:39
  • $\begingroup$ What they said ie size does not affect time taken (by definition) BUT larger objects have more air drag so take more energy to move through air at the same speed. ROUGHLY energy required is proportional to frontal area for equal shapes and to the CUBE of the speed. $\endgroup$ – Russell McMahon Jul 27 '15 at 12:54

Time taken to cover a distance L by an object moving at a speed V is given by $$ t = \frac{L}{V} $$ where t is the time taken.

Therefore, the size of the object does not matter at all. Whatever be the size of two objects; if they have the same speed, they will cover the same distance in a given time.

But, usually objects with a better aerodynamic design will move faster (i.e. have a greater speed) than a similar object with a poor aerodynamic design.


There is one, very limited and very deceptive, experimental case in which a large object can "cover more distance" than a smaller object at the same speed:

Say you have two small cannons in a gymnasium and are going to launch two projectiles - a round cannonball and a long pole - to the opposite wall. The gymnasium wall is 100ft from the back of each cannon, and the cannons fire their projectiles at 10ft/s, so each should cover the distance in the same amount of time. However the pole, being ten feet long, hits the far wall 0.9s before the cannonball, which is only 1ft in diameter, so it could be interpreted that the pole covers the distance faster than the ball.

However there's a distinction to be made here: the front of the pole hits the wall first only because it gets a head start: when the pole hits the wall, the ball is still 9ft away, which makes sense because it was 9ft behind to begin with. The back of each projectile, however, is 10ft from the wall when the pole front contacts the wall, which again makes sense because they started at the same distance - the back of each cannon - so it is (correctly) measurable that the speed of each is the same regardless of size. The pole travels 90ft in 9 seconds, and the ball travels 99ft in 9.9s: 10ft/s for each.


There is no size or weight in speed
The speed of an object does not depend on its size or its weight
The units for speed is distance / time

Distance is speed X time

100 miles / hour for time of 1 hour

(100 miles / hour) X 1 hour = 100 miles

  • $\begingroup$ This answer does not appear to address the question asked. You have not addressed the issue of the size of the object travelling.... $\endgroup$ – tom Jul 27 '15 at 21:26
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    $\begingroup$ @tom First sentence. What part of "There is no size or weight in speed" is not clear? And it is the only answer that addresses moves at speed of say 100 mph for an hour. $\endgroup$ – paparazzo Jul 27 '15 at 21:28
  • $\begingroup$ Ok Frisbee - I see what you mean, but it could be more explicitly state like "The speed of an object does not depend on its size or its weight" $\endgroup$ – tom Jul 27 '15 at 21:39

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