When we carry this process to its logical conclusion, we are left with an infinitesimally small interval. Over such an interval, the average velocity becomes the instantaneous velocity or the velocity at a specific instant.
Police give tickets based on instantaneous velocity, but when calculating how long it will take to get from one place to another on a road trip, you need to use average velocity. Instantaneous velocity v is the average velocity at a specific instant in time or over an infinitesimally small time interval. Mathematically, finding instantaneous velocity, v , at a precise instant t can involve taking a limit, a calculus operation beyond the scope of this text.
However, under many circumstances, we can find precise values for instantaneous velocity without calculus. In physics, however, they do not have the same meaning and they are distinct concepts.
One major difference is that speed has no direction. Thus speed is a scalar. Just as we need to distinguish between instantaneous velocity and average velocity, we also need to distinguish between instantaneous speed and average speed.
Instantaneous speed is the magnitude of instantaneous velocity. At that same time his instantaneous speed was 3. Average speed, however, is very different from average velocity. Average speed is the distance traveled divided by elapsed time. We have noted that distance traveled can be greater than displacement.
So average speed can be greater than average velocity, which is displacement divided by time. Your average velocity, however, was zero, because your displacement for the round trip is zero. Displacement is change in position and, thus, is zero for a round trip.
Thus average speed is not simply the magnitude of average velocity. Figure 3. During a minute round trip to the store, the total distance traveled is 6 km. The displacement for the round trip is zero, since there was no net change in position.
Thus the average velocity is zero. Another way of visualizing the motion of an object is to use a graph. A plot of position or of velocity as a function of time can be very useful. For example, for this trip to the store, the position, velocity, and speed-vs. Note that these graphs depict a very simplified model of the trip.
We are also assuming that the route between the store and the house is a perfectly straight line. Figure 4. Position vs. Note that the velocity for the return trip is negative. If you have spent much time driving, you probably have a good sense of speeds between about 10 and 70 miles per hour. But what are these in meters per second? To get a better sense of what these values really mean, do some observations and calculations on your own:.
A commuter train travels from Baltimore to Washington, DC, and back in 1 hour and 45 minutes. The distance between the two stations is approximately 40 miles. It is commonly used in different commodities.
It is commonly used in measuring large amount of liquid such as gasoline. Unlike the other two temperature scales, the Kelvin scale does not use degrees. Its zero point, 0 K, is defined as the coldest possible temperature which is also called absolute zero.
Contact Us. Grades 6 7 8 9 10 11 Toggle navigation. Physical Quantities and Their Units. The following are the basic quantities being measured and the respective units used: 1.
Length Length — describes how long something is. Units of Length. A weighing scale is an instrument commonly used for measuring the mass of fruits, vegetables, and meat. The scale is calibrated in grams and kilograms. Units of Mass. A clock is a common instrument for indicating time.
It shows the time in hours, minutes, and sometimes in seconds. Units of Time. Second s minute min hour hr day d week wk month mo year yr.
A football field usually measures about 1 hectare. Units of Area. A measuring cup is a kitchen utensil used to measure the volume of liquid or ingredients like flour and sugar. A gasoline container usually measures 1 gallon.
Units of Volume. The thermometer is the most common instrument for measuring temperature. There's a lot of activity going on under the hood of the OS, which is very likely to mess up your time measurements. In order to improve the accuracy of the measured times you should execute the tests multiple times and remove the lowest and the greatest times from the final results. This approach will exclude most of the external factors that may influence your code's execution time and will serve you well in most cases.
The Stopwatch class is used to measure time as it is much more accurate than using DateTime. You can easily make a test class to automate this. I have published one such class in my blog. All you have to do is to override the Method1 and Method2 methods putting there the code fragments you want to test and use the test class like this:. You may have to apply some statistical techniques here to iron out the variance.
Try running the same piece of code times and then take the average time, and compare that. Simulations usually employ some sort of methods to 'clean up' the numbers, and this is one of those. Generally: Don't look at the wallclock time but the CPU time consumed by your process to determine how long it ran.
Especially for things that are just computation this is much more reliable because it will be unaffected by other processes running at the same time. The trouble with all the clock-based approaches is that you are never quite certain what you are timing. You might, whether you realise it or not, include in your timing:.
I'm not saying that all of these apply to this particular timing but to timings in general. So you should supplement any timing you do with some consideration of how many basic operations your alternative codes execute -- some considerations of complexity not ignoring as we usually do the constant terms. And make sure, if you take this approach, that you don't inadvertently speed up the second trial by having data already loaded after the end of the first trial.
I'll have to recommend the highly profiler included in Visual Studio Team Suite or Development Edition or the upcoming Visual Studio Premium or Ultimate is even better as the best way. It is highly configurable, extremely powerful, dead simple to use, very fast, and works with both native and managed code.
I'm not familiar with the workflow of ANTS , but that appears to be another option. Without a doubt using a profiler is the only option for a developer that is concerned with their application's performance. There is no substitute, and you really can't take any commercial developer working on performance that would pass up a profiler seriously. However, if you are interested in measurements for one of the following, you may not have access such a profiler, in which case the Stopwatch class can form a basis for your measurement technique:.
You can also use log4net, simply add log. Info "Test" where you wanna track stuff and you will find all your info and the time that line was executed in a txt file, for example: , [9] INFO Hms. How are we doing? Please help us improve Stack Overflow. Take our short survey. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. What is the best way to measure how long code takes to execute?
Ask Question. Asked 11 years, 10 months ago. Active 2 years, 11 months ago. Viewed 73k times. I'm trying to determine which approach to removing a string is the fastest. I simply get the start and end time and show the difference. What is a better method to get more accurate results?
Collections; using System.
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