An external force is a force that acts on an object from outside the object. In other words, it is a force that is not caused by any of the object's internal components or interactions. External forces can be either contact forces or non-contact forces.

Examples of external contact forces include:

- A person pushing on a wall

- A book resting on a table

- A car colliding with another car

Examples of external non-contact forces include:

- Gravitational force

- Magnetic force

- Electric force

External forces can cause an object to move, change its shape, or both. For example, if you push on a wall, the wall will move in the direction that you are pushing it. If you drop a book, the book will fall to the ground due to the force of gravity.