Force

In physics, a force is an external cause responsible for any change of a physical system. For instance, a person holding a dog by a rope is experiencing the force applied by the rope on his hand, and the cause for its pulling forward is the force exercised by the rope. The kinetic expression of this change is, according to Newton's second law, acceleration, non kinetic expressions such as deformation can also occur. The SI unit for force is the newton.

Forces in the laboratory

Founding experiments

• Galileo Galilei used rolling balls to disprove the Aristotelian theory of motion (1602 - 1607)
• Henry Cavendish's torsion bar experiment measured the force of gravity between two masses (1798)

Instruments to measure forces

• spring balance
• pivot balance
• forcemeter