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# Mechancis M1 constant retardation question. Watch

1. In this video a particle is constantly decelerating. And somehow it turns around? Is this because if you decelerate you will come to a halt and then if you decelerate even more you will start to reverse?[https://www.youtube.com/watchv=UD52y...61DC&index=17]

Retardation means to slow down... I don't understand how you can slow down at 0 m/s^-1. Please help explain.
2. (Original post by MathsMeister)
In this video a particle is constantly decelerating. And somehow it turns around? Is this because if you decelerate you will come to a halt and then if you decelerate even more you will start to reverse?[https://www.youtube.com/watchv=UD52y...61DC&index=17]

Retardation means to slow down... I don't understand how you can slow down at 0 m/s^-1. Please help explain.
I can't watch the video but I think I understand what you mean. Essentially decelerating in one direction is accelerating in the opposite direction. So when the particle reaches 0m/s^-1 it's can't slow down anymore, clearly, but keeps accelerating in the opposite direction, and so it's velocity will become negative. Hopefully I have explained this well enough haha

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3. (Original post by MathsMeister)
In this video a particle is constantly decelerating. And somehow it turns around? Is this because if you decelerate you will come to a halt and then if you decelerate even more you will start to reverse?[https://www.youtube.com/watchv=UD52y...61DC&index=17]

Retardation means to slow down... I don't understand how you can slow down at 0 m/s^-1. Please help explain.
Remember that velocity and acceleration are vector quantities. If something has a velocity in the positive direction and its acceleration is in the negative direction (retardation) then its velocity can have magnitude zero at some point, and thereafter the object can change direction and have a velocity in the negative direction.
4. Velocity is speed but with a direction, lemme give you an example.

A ball is projected upwards, the velocity is positive but the acceleration is negative due to gravity. Eventually that ball will come back down, the velocity is negative now as it's in the opposite direction.

Feel free to message me if you need more help

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