You can't produce acceleration in a body without applying an external force. This is a fundamental principle of physics known as Newton's Second Law of Motion:

F = ma

Where:

* F is the net external force acting on the body

* m is the mass of the body

* a is the acceleration of the body

This equation tells us that acceleration is directly proportional to the net force and inversely proportional to the mass. Therefore, if there is no net external force acting on a body, its acceleration will be zero.

However, there are a few scenarios that might seem like acceleration without an external force:

* Gravity: Gravity is a force, not a result of a force. It's an inherent property of objects with mass, and it causes acceleration. So, while it may appear that objects accelerate towards the Earth without an external force, gravity is the force acting on them.

* Fictitious forces: These forces are not real forces but rather appear as forces due to non-inertial reference frames. For example, in a car accelerating, you might feel pushed back into your seat. This "force" is not real; it's a result of the car's acceleration and your inertial tendency to stay at rest.

In conclusion, while there are situations that might seem like acceleration without external forces, it's important to remember that acceleration is always caused by a net external force.