Title text:
Unstoppable force-carrying particles can't interact with immovable matter by definition.
Transcript:
[An arrow pointing to the right and a trapezoid are labeled as 'Unstoppable Force' and 'Immovable Object' respectively.]
[The arrow is shown as entering the trapezoid from the left and the part of it in said trapezoid is coloured gray.]
[The arrow is shown as leaving the trapezoid to the right and is coloured black.]
[Caption below the panel:] I don't see why people find this scenario to be tricky.
Source: https://xkcd.com/3084/
It may be worth it to decide how we define ‘unstoppable force’ and ‘immovable object’.
An Immovable Object has 0 velocity:
v = 0
Acceleration is the time derivative of velocity:
a = d/dt(v(t))
a = d/dt(0)
a = 0
And we know that
a = F~net~ / m
An object with infinite mass would satisfy this equation, but an object with no net force would too. We could add a correction force that will satisfy the constraint of 0 net force.
|F~net~| = 0
∑F~i~ = 0
F~correction~ + … = 0
To satisfy Newton’s 3rd law, we would need a reaction force to our correction force somewhere, but let’s not worry about that for now.
A physics definition of ‘Unstoppable Force’ is:
|F~unstoppable~| =/= 0
In this case the gravitational force fits this description, given a few constraints
F~g~ = Gm∑ M~i~ / x~i~^2^
As long as the gravitational constant G is not 0, our object has mass, and
∑ M~i~ / x~i~^2^ =/= 0, then
|F~g~| > 0
But this does feel kinda like cheating because it’s not really what people mean by ‘unstoppable force’. the other way to define it is just immovable object in a different reference frame.
a = 0, |v| > 0
I’m gonna stop here because this is annoying to type out on mobile