The instrument that measures the force needed to move an object along a surface is called a friction tester.

Here's why:

* Friction is the force that opposes motion between two surfaces in contact.

* A friction tester is designed to apply a controlled force to an object resting on a surface.

* By measuring the force required to initiate or maintain movement, the tester determines the coefficient of friction between the object and the surface.

Note: Other instruments like load cells and force sensors can also be used to measure force, but they are not specifically designed for friction measurement.