For the analysis, we will use a moving reference frame attached to the rotating disk. Using this in Newton's 2nd law, we determine the contact force F acting on the particle. It is seen that the ...

Forces are divided into contact forces and non-contact forces ... You cannot see a force but you can see its effect. For example, when you apply a force to push a door open.

A force is a push or a pull. Contact forces arise between two objects which are in contact. Friction close frictionA force that opposes or prevents movement and converts kinetic energy into heat.