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Course: Class 9 Physics (India) > Unit 1
Lesson 3: Instantaneous speed and velocityInstantaneous speed & velocity
Let's learn what instantaneous speed & velocity are. Created by Mahesh Shenoy.
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- If (as said by the respected teacher) instantaneous velocity is 0, then how come calculus or both ways could find the numeral excluding 0 ?(2 votes)
- the thing that the formula finds is not exactly instantaneous velocity. it is just as close as you can get to the instantaneous velocity. very clever invention by sir newton. he was a genius.(2 votes)
- is the instantaneous speed is the magnitude of instantaneous velocity?(1 vote)
- yes, instantaneous speed is just how fast something is moving in the instant that we are looking at it. the direction doesnt matter, like it does with inst. velocity(2 votes)
- Can someone explain the second way of finding instantaneous velocity?>(1 vote)
- The second method uses the kinematic formulas to get the velocity(v) at any time(t)
Learn more about kinematic formulas here:
https://www.khanacademy.org/science/physics/one-dimensional-motion/kinematic-formulas/a/what-are-the-kinematic-formulas
https://www.khanacademy.org/science/ap-physics-1/ap-one-dimensional-motion/motion-with-constant-acceleration/v/choosing-kinematic-equations(2 votes)
- Is their a less difficult way to solve instantaneous Velocity questions??(1 vote)
- So here are my thoughts, please tell me if im wrong.
i think what sir newtons instantaneous velocity is is not a perfect instantaneous velocity. it is just as close as we can get to an instant without eliminating the concept of time. time is just relative change with respect to a fixed regular intervaled change like the moving of the sun or the hands of a clock. but in reality time doesnt exist for a system in which there is only one object and the condition that the system cant be ever used as a reference. due to that, the instantaneous and the average and the overall velocity will always be zero for things when we just look at those things alone. in reality, motion, force, displacement, distance, speed, velocity, etc etc anything that uses the concept of time can not exist for a single object only system. Due to time being a relative measurement, these all quantities also become relative concepts. They are good to predict the interactions and the positions of objects with respect to each other in a fixed "time period" but if theres no things to relate an objects activities to. then those activities just dont exist. so if we talk and think about just one object, then we cannot consider it moving its just changing maybe and we can not calculate the speed or anything because for that we require time which intriduces another changing object in the system.(1 vote)
Video transcript
pretend you were a physics student you were just getting out of class you were walking home when you remembered that there was a galaxy Wars Marathon on tonight so you do what every physics student would do run you're pretty motivated to get home so say you start running at 6 meters per second maybe it's been a while since the last time you ran so you have to slow down a little bit to 2 meters per second when you get a little closer to home you say no captain Antares wouldn't give up and I'm not giving up either and you start running at 8 meters per second and you make it home just in time for the opening music these numbers are values of the instantaneous speed the instantaneous speed is the speed of an object at a particular moment in time and if you include the direction with that speed you get the instantaneous velocity in other words eight meters per second to the right was the instantaneous velocity of this person at that particular moment in time note that this is different from the average velocity if your home was a thousand meters away from school and it took you a total of 200 seconds to get there your average velocity would be five meters per second which doesn't necessarily equal the instantaneous velocities at particular points on your trip in other words let's say you jogged 60 meters in a time of 15 seconds during this time you were speeding up and slowing down and changing your speed at every moment regardless of the speeding up or slowing down that took place during this path your average velocities still just gonna be 4 meters per second to the right or if you like positive 4 meters per second say you wanted to know the instantaneous velocity at a particular point in time during this trip in that case you'd want to find a smaller displacement over a shorter time interval that's centered at that point where you're trying to find the instantaneous velocity this give you a better value for the instantaneous velocity but it still wouldn't be perfect in order to better zero in on the instantaneous velocity we could choose an even smaller displacement over that even shorter time interval but we're gonna run into a problem here because if you want to find a perfect value for the instantaneous velocity you'd have to take an infinitesimally small displacement divided by an infinitesimally small time interval but that's basically 0/0 and for a long time no one could make any sense of this in fact since defining motion at a particular point in time seemed impossible it made some ancient Greeks question whether motion had any meaning at all they wondered whether motion was just an illusion eventually Sir Isaac Newton developed a whole new way to do math that lets you figure out answers to these types of questions today we call the math that Newton invented calculus so if you were to ask a physicist what's the formula for the instantaneous velocity he or she would probably give you a formula that involves calculus but in case some of you haven't taken calculus yet I'm going to show you a few ways to find the instantaneous velocity that don't require the use of calculus the first way is so simple that it's kind of obvious if you're lucky enough to have a case where the velocity of an object doesn't change then the formula for average velocity is just gonna give you the same number as the instantaneous velocity at any point in time a third way to find the instantaneous velocity is for another special case where the acceleration is constant if the acceleration is constant you can use the kinematic formulas to find the instantaneous velocity V at any time T you