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While standing somewhere, we can accelerate a RC car more or less using the remote control toggle. The electric motor then applies a varying force ##F## to the car's wheels depending on when we act on the toggle. Does that varying force represent an example of a time-dependent force ##F(t)## since it varies according to the time we act on the toggle? However, from the car's perspective, the force varies with time but the car occupies a certain position in time, i.e. ##t(x)##, so the force can be implicitly made to depend on the position coordinate ##x## of the car as well....

As another example, a mass attached to a horizontal, oscillating spring, experiences a force ##F(x)=-kx## which depends on the spring position. Everytime the mass is the position ##x##, the force is the same, regardless of when it is there, so the force is not dependent on time. However, the mass position is a function of time, ##x(t)##, so we could write the spring force ##F(x)## as function of t and all of a sudden the spring force becomes a function of time: ##F(t)##. So, should we state that the spring force is a position-dependent force in an absolute sense or is it equally a time-dependent force since the force, from the oscillating mass perspective, is different at different time instants?

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# I Force as a function of time/space

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