Speed is distance multiplied by time -- Is this correct?

[Rev. Cheeseman]

TL;DR Summary

Using an online converter, I get a different result

Hello,

In this study https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9784821/, the distance the punch travelled from start to impact is 0.49 meters and the time taken from start of punch (that's it, they define the start of punch as the moment the elbow first start to extend) to impact is 0.1 second. The velocity of the fist at impact is 8.9 meter per second. I use an online speed, time and distance calculator I got 4.9 meter per second. Why is that? Thank you.

 

[Demystifier]

Speed is certainly not equal to distance times time, obviously you meant distance divided by time. But this is true only for constant speed, and in the case you consider the speed is not constant. That's why 4.9 meter per second is wrong.

 

[Drakkith]

The velocity of the fist at impact is 8.9 meter per second. I use an online speed, time and distance calculator I got 4.9 meter per second. Why is that?

Because speed = distance / time, and 0.49 divided by 0.1 is 4.9.
Note that the units themselves tell you this: meters per second. Meters/seconds. Distance over time.

How you calculated 8.9 meters per second I cannot say. If you multiplied instead of dividing you would come up with 0.049, not 8.9.

 

[Rev. Cheeseman]

Speed is certainly not equal to distance times time, obviously you meant distance divided by time. But this is true only for constant speed, and in the case you consider the speed is not constant. That's why 4.9 meter per second is wrong.

Oh I'm sorry for the mistake, yes it should be distance divided by time. Thus, 4.9 meter per second is more like average velocity and it will be 4.9 meter per second only if the speed or velocity is constant? Sorry, my English is not really good.

 

[Rev. Cheeseman]

Because speed = distance / time, and 0.49 divided by 0.1 is 4.9.
Note that the units themselves tell you this: meters per second. Meters/seconds. Distance over time.

How you calculated 8.9 meters per second I cannot say. If you multiplied instead of dividing you would come up with 0.049, not 8.9.

Sorry it is actually distance divided by time.

The velocity should be 4.9 meter per second if we divided 0.49 meter with 0.1 second, but in the study in the link given the actual speed is 8.9 meter per second which means the distance should be 0.89 meter.

 

[Demystifier]

Thus, 4.9 meter per second is more like average velocity and it will be 4.9 meter per second only if the speed or velocity is constant?

Yes, exactly!

 

[Rev. Cheeseman]

Yes, exactly!

Thank you so much.

 

[Rev. Cheeseman]

Yes, exactly!

I'm sorry, one more thing. Therefore, assuming if the distance from the start of a punch to the impact pad is 1 meter and the time taken for the punch to reach the impact pad is 0.3 second. The real velocity of the punch will be likely to exceed 3.3 meter per second too?

 

[Demystifier]

I'm sorry, one more thing. Therefore, assuming if the distance from the start of a punch to the impact pad is 1 meter and the time taken for the punch to reach the impact pad is 0.3 second. The real velocity of the punch will be likely to exceed 3.3 meter per second too?

Yes, of course.

 

[Rev. Cheeseman]

Yes, of course.

Thank you.