(1) Method 1: Use a spring dynamometer to pull the object to move in a straight line at a uniform speed to the right on the horizontal plane. The dynamometer indicates that the friction force on the object is 3.6 N as shown in Figure A; When the tension increases to 5N, the friction force on the object is 3.6 N. 。
(2) Method 2: As shown in Figure B, the board A stretches and moves on the horizontal ground with a horizontal force F of 3N, while B is still. At this time, the pointer of the spring dynamometer connected with B is 2N, so the friction force acting on B is 2N, and the direction is horizontal to the right; If you add a towel to the desktop and board A, and then increase F to pull A, the friction on B will remain unchanged.
Extended data
Analysis (1) The object moves at a uniform speed and is in a state of equilibrium. Friction and tension are a pair of balanced forces, so friction equals tension. The factors affecting sliding friction are: pressure and roughness of contact surface;
(2) When the object B is at rest, it will be influenced by the balance force, and the magnitude and direction of the friction force can be judged according to the knowledge of the balance force;
The factors affecting sliding friction are pressure and roughness of contact surface.