# FM1 - Direction of impulse when there is a collision between two particles

How do I work out the direction of impulse between two particles when they collide? I'm just going through the Further Mechanics 1 content and I'm doing decently with the Coefficient of Restitution stuff but I'm finding it hard to actually work out the direction of Impulse.

Can you generalise a way to determine this?

Original post by vnayak
How do I work out the direction of impulse between two particles when they collide? I'm just going through the Further Mechanics 1 content and I'm doing decently with the Coefficient of Restitution stuff but I'm finding it hard to actually work out the direction of Impulse.

Can you generalise a way to determine this?

An impusle is an integration of force with respect to time, so its really a question of which way the force acts on the object. Here there are two objects and they exert an equal and opposite force/impulse on each other during the collision - hence the conservation of momentum.
(edited 1 month ago)
Original post by mqb2766
An impusle is an integration of force with respect to time, so its really a question of which way the force acts on the object. Here there are two objects and they exert an equal and opposite force/impulse on each other during the collision - hence the conservation of momentum.
So the impulse experienced by the two particles is the same? Therefore, I'll be able to do the change in momentum on either of the particles and then get the impulse right?

I don't have a Physics Background so Mechanics really isn't my strong suit 😭 but I'm doing my absolute best to improve in it.

Original post by vnayak
So the impulse experienced by the two particles is the same? Therefore, I'll be able to do the change in momentum on either of the particles and then get the impulse right?

I don't have a Physics Background so Mechanics really isn't my strong suit 😭 but I'm doing my absolute best to improve in it.

The magnitude of the impulses is the same, but the signs are different as they are in opposing directions. For two objects m,u,v and M,U,V and constant acceleration (force) assumption
mv = mu + mat
MV = MU + MAt
(just multiply through v=u+at by the two masses). By newton 3
ma = -MA
so
mv-mu = mat = -MAt = MU-MV
or
mu+MU = mv + MV
so the conservation of momentum comes from the impulses mat, MAt being applied to the two objects and them being equal but opposite signs.