# I Vectors and vector sum

1. May 8, 2016

### prashant singh

Suppose if I applied a 4N force and then 2N force on an object , what will be total force. Note I didn't said simoultaneously, I mean one after the other, then what will be the total force , I think 6N , i know about vector sum and etc.. but I think this question doesn't makes any sense. What's your opinion. vector addition and vector algebra is applied for simoultaneous force(vectors).

2. May 8, 2016

### Math_QED

What's the direction of the forces?

3. May 8, 2016

### FactChecker

No. A time sequence of forces is not equivalent to the sum of those forces at a single time. If you graphed the acceleration and associated velocities over time, you would see that you will not get the same result from the two cases.

4. May 8, 2016

### prashant singh

I think this question doesn't makes any sense because vector algebra is applied for simooultaneous vectors(here force). I think direction doesn't matters but u can take both in same direction.

5. May 8, 2016

### FactChecker

That depends on how you are using the vectors. If a person moves from A to B and then from B to C, you can add two motion vectors AB and BC to get the total motion vector AC. But force doesn't work that way.

6. May 8, 2016

### prashant singh

I think this question doesn't makes any sense because vector algebra is applied for simooultaneous vectors(here force). I think direction doesn't matters but u can take both in same direction.

7. May 8, 2016

### Staff: Mentor

The magnitudes of the forces add like this only if the forces are acting in the same direction.

Of course the direction matters.

Also, "textspeak" such as "u" for "you" is not allowed at this site.

8. May 8, 2016

### prashant singh

Okk sorry for using u

9. May 8, 2016

### prashant singh

Can we add two vectors which are not acting simoultaneously by the vector law of addition.

Last edited by a moderator: May 8, 2016
10. May 8, 2016

### Staff: Mentor

I don't think that makes sense. If you have some object that is moving along a path, and you apply a force to it, that force could cause the object to change direction (or not, all depending on the direction of the force and the direction the object is moving). If later a different force is applied, then that could cause a different resulting direction for the object. To the best of my knowledge, you don't add vectors that aren't acting simultaneously (simoultaneously is not a word).

Also, if the two forces are applied at different times (i.e., not simultaneously), how much time elapses between the times of the two forces? One second, one hour, one week, ten years?

Last edited: May 8, 2016
11. May 8, 2016

### prashant singh

Exactly

12. May 9, 2016

### SammyS

Staff Emeritus
You can if it makes sense for the context of the situation . For instance a displacement of 3km due north followed by a displacement of 4km due east. Those displacement vectors can be added to give the overall displacement.

This sort of vector addition does not make sense if one force is followed by a second force.