In physics, there’s a concept called the conservation of momentum. This means that in a system where nothing from the outside is messing with it, the total momentum stays the same. But when outside forces come into play, they can change the momentum a lot.

Effects of External Forces:

1. What Are External Forces?
   External forces come from outside the system. They include things like gravity, friction, and any pushes or pulls we apply.

2. How They Affect Momentum:

   • Momentum ($p$) is a way to describe how much motion an object has. It’s calculated by multiplying the object's mass ($m$) by its speed or velocity ($v$):
     $p = mv$

   • According to Newton's second law, if there’s an outside force ($F$) acting on an object, this force changes the momentum over time:
     $F = \frac{dp}{dt}$

   • If the total outside force acting on a system isn’t zero ($F_{net} \neq 0$), then the momentum will change.

3. Numbers and Changes in Momentum:

   • If we look at an object’s starting momentum ($p_i$) and its ending momentum ($p_f$), we can find the change in momentum:
     $\Delta p = p_f - p_i$

   • When a force acts for a certain time, we can calculate something called impulse ($J$), which is related to how momentum changes:
     $J = F \Delta t = \Delta p$

Looking at an Isolated System:

• If no outside forces are acting on a system ($F_{net} = 0$), then:
  $p_i = p_f$
  This means the total momentum stays the same.

• But when we have outside forces acting:

  • For example, if a 10 Newton force (that’s how strong a push is) acts on a 2 kg object for 3 seconds, we can figure out the change in momentum:
    $J = F \Delta t = 10 \, \text{N} \times 3 \, \text{s} = 30 \, \text{Ns}$
    This shows a change in momentum of 30 kg·m/s.

In Summary:

External forces are very important when studying momentum because they change the way momentum behaves in a system. The idea of conservation of momentum only works when these outside forces are not present. So, understanding how these forces affect momentum is key to predicting how objects will move and act within a system.