Force
Force is an interaction between objects that can change an object’s motion, speed, direction, or shape. Forces are mainly divided into contact forces and non-contact forces. Contact forces act when objects physically touch each other. Examples include friction, which opposes motion between surfaces, and air resistance, which acts against an object moving through the air. Non-contact forces act from a distance without direct physical contact. These include gravitational force, which attracts objects with mass, magnetic force, which causes attraction or repulsion, and electrostatic force, which acts between electrically charged objects. When the forces acting on an object are balanced, the net force is zero and its motion does not change. When the forces are unbalanced, the net force causes the object to speed up, slow down, or change direction.