Here is a case where we have vertical circular motion, a pendulum or swing, where it is a bit more complicated than horizontal circular motion. For a pendulum, the tension and gravity components vary with the angle, so we have non-constant forces and acceleration. This could be tough to solve with Newton's laws. However, with energy we can find speeds more easily, and this will allow us to find the tension in the string for any angle of its motion. Check it out.
Showing posts with label circular motion of particles. Show all posts
Showing posts with label circular motion of particles. Show all posts
Monday, January 9, 2012
Monday, April 26, 2010
How to think about mass spectrometers
We know that electric charges moving in magnetic fields feel a force, called the Lorentz force, which is a cross product: F = qv x B.
This force is always perpendicular to the motion and B-field, and because of this particles get pushed into circular paths. This means the centripetal force is determined by the magnetic force. No work is done, as the energy is unchanged, but just the direction of the particle is changed.
In order to get a mass spectrometer to work, we also need to know the velocity of the particles. We can use electric fields to create a velocity selector. Keep in mind there is a good ActivPhysics simulation for mass spectrometers, 13.10, you may want to check out, too.
This force is always perpendicular to the motion and B-field, and because of this particles get pushed into circular paths. This means the centripetal force is determined by the magnetic force. No work is done, as the energy is unchanged, but just the direction of the particle is changed.
In order to get a mass spectrometer to work, we also need to know the velocity of the particles. We can use electric fields to create a velocity selector. Keep in mind there is a good ActivPhysics simulation for mass spectrometers, 13.10, you may want to check out, too.
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