1. The problem statement, all variables and given/known data I am having trouble with a basic deflection problem - a single proton travelling through a magnetic field: v = Velocity of the proton = 6 000 000 meters per second (1/50th the speed of light, so no relativistic effects) B = magnetic field strength = 0.5 Tesla Charge of proton q = + 1.60217e-19 Coulombs Mass of proton m = 1.67262e-27 kg Direction = zero radians 2. Relevant equations Force = q*v*B sin(theta) Radius=(Mass*sqr(Velocity))/Force Period:=(2*pi*Radius)/Velocity Force=Mass*Acceleration 3. The attempt at a solution First I find the maximum force on the proton due to its charge and velocity through the field: Force = q*v*B sin(theta) In this case the proton is travelling perpendicular to the field, so sin(theta) = 1 and the magnitude of the force is simply: Force = q*v*B = 4.8065e-13 Newtons Now that is fine, and if I want the radius of the circle described by the proton in the field I can use: Radius=(Mass*sqr(Velocity))/Force or r=mv/qB = 0.125 meters or 125mm Which is particularly satisfying, because it relates such high speed, low mass and charge into a realistic spatial dimension. I can also find the time that it takes to complete one revolution: Period:=(2*pi*Radius)/Velocity =131.19e-9 seconds or 131 nanoseconds. But what I would like to find is the instantaneous position and direction after a given time, say 1 nanosecond. I tried dividing the circumference by 131 nanoseconds, but I feel like this is cheating. I also tried to use Acceleration = Force/mass, but in this case the acceleration is only a change in direction, not in velocity.