 Today I'm going to recap how we can understand the gravitational force, electric force, and magnetic force using the model of fields. Let's start with the gravitational field. In order to make a gravitational field, an object needs mass. The field lines point towards the center of that mass, and the strength of the field is indicated by how closely spaced the lines are. Closer lines mean a stronger field. When a particle with mass is in the field, it will experience a gravitational force in the same direction as the gravitational field. That's pretty easy. For gravity, the force and field are always in the same direction. Now let's look at electric fields. In order to make an electric field, an object needs charge. There are two natures of charge, positive and negative, and the electric field lines go towards the negative charges and away from the positive charges that are creating the fields. When a particle is in an electric field, it only experiences an electric force if it has a charge. If the particle has a positive charge, it experiences a force in the same direction as the electric field. And if it has a negative charge, the particle experiences a force in the opposite direction as the electric field. Now let's think about magnetic fields. Magnetic fields are created by permanent magnets, or charges moving through conductors, and you can click on this video I made about the first and second hand rules to see how that works. In order to experience a magnetic force, a particle again has to have charge, but now it also has to have velocity. The nature of the charge and the direction of the velocity determine the direction of the force, and it can be worked out using the third left or right hand rule. The force will always be at a right angle to the magnetic field, which is unique compared to the electric and gravitational fields. Now let's look at the motion of our particles in the different types of fields. In a gravitational or electric field, there are two types of motion we can get. If the particle is moving parallel to the field, the particle will experience a force in the same dimension as its velocity, and it will have linear accelerated motion. It will speed up or slow down in a straight line. If the particle is moving perpendicular to the field, the force will start off at a right angle to the velocity, and it will get motion in a parabola, just like projectile motion. Finally, the magnetic field. If a particle moves in the same dimension to the magnetic field, we get no force produced, and the particle has uniform motion. But if the particle moves at a right angle to the field, we get a magnetic force which is always at a right angle to the velocity through the entire motion of the particle, which causes uniform circular motion. If you're looking for more information on the mathematical models that describe the motion of these particles, check out these other videos on my YouTube channel. Thank you.