Physics Asked on May 13, 2021
I’m an A2 igsce math student and I’m taking mechanics for the first time in math this session. However, I was adviced to ask this question in the physics forum instead.
I know that what I’m going to say is wrong judging from my teacher’s reaction when I asked him about this but unfortunately he didn’t explain to me why it’s wrong.
So, when we draw two forces on an object, we usually assume that they are applied at the same time but do we also assume that they were applied for a certain duration of time, like one second maybe?
I mean, how are we supposed to get the magnitude of the resultant of these two forces meanwhile we don’t know the duration? To make my point clearer, for example, couldn’t there be more than one force in the exact direction of the resultant force that would make our object/point reach the final speed it is supposed to reach after these two forces are applied for a certain time? — thinking about it now the examiner never mentions for how long two forces should be applied, but anyway.
But each force would need a certain amount of time, like a weaker force will need more time while a stronger one will take less time and so on. And all these forces are in the same direction of the resultant force of course.
This question is brilliant, In the many institutions the time duration of two forces are assumed to be of the same duration to make things similar but anyway if you think of weak force and a strong force there is no problem to consider them being played on different durations but this might affect the answers.
Time is usually denoted by a scalar that is a number or a interval that is associated with the vector.
Answered by user285989 on May 13, 2021
One has not to confuse forces and effects of the forces. The resultant force's effect is the motion of the system to which the force has been applied. This motion is certainly different if a given force acts for a longer or shorter time. But the second Newton's law says that the acceleration at a given time $t$ is given once one knows the force at the same time. The instantaneous force information is encoded into a second-order differential equation whose solution automatically takes into account the time-span each individual force has been applied.
Answered by GiorgioP on May 13, 2021
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