This law tells us that an object can have something called a “charge,” and, if it does have a charge, forces can be exerted on the object which are not caused by something in contact with it. We can measure these forces as we measure other forces, for example by measuring the acceleration it causes and the mass of the charged object, or by balancing it with a known force, such as that exerted by a spring with a particular compression and known spring constant.
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We see from Lorentz’s law that the electromagnetic force on an object is the product of the charge on it and a vector quantity which is the sum of two terms. The first of these terms is independent of the charged object’s velocity, and the second is dependent on the object’s velocity and always perpendicular to it. Both terms can depend on the object’s position and on time.
