Forces

A force is a push or a pull that can change the motion or shape of an object. In physics, forces explain why objects start moving, stop, speed up, slow down or change direction. They are measured in newtons (N), named after Isaac Newton, whose laws of motion describe the relationship between forces and movement.

Forces can act through direct contact, such as friction, tension or the force applied by a hand, or at a distance, as with gravity, magnetism and electric forces. When the forces acting on an object are balanced, they cancel each other and the object's motion does not change. If the forces are unbalanced, the object accelerates in the direction of the resulting force.

The greater the mass of an object, the more force is needed to produce the same acceleration. Forces are involved in almost everything that happens around us. Gravity keeps planets in orbit around the Sun, causes objects to fall toward Earth and gives them weight. Friction allows people to walk without slipping, helps vehicles brake and generates heat when surfaces rub together.

Air resistance slows the motion of falling or moving objects, while buoyant force enables boats to float and balloons filled with helium to rise. Engineers and scientists study forces to design safe buildings, bridges, vehicles, aircraft and machines. Understanding how forces interact makes it possible to explain everyday events, predict the motion of objects and develop technologies used in transportation, construction, sports and space exploration.