g You can use the pin in the knee joint as the pivot point, and the red dot marks the center of mass for the lower leg. Choose an angle between 15 and 30 degrees to make your measurements.

it is a negative acceleration

force is based upon mass and acceleration.the statement is not always true.

it can be explained from newton's second law of motion.

as per newton's second law of motion the rate of change of momentum is directly proportional to the applied force and takes place along the direction of force.

mathematically it can be written as -

                                              ⇒      

here   k is the proportionality constant whose value is 1.

                                                            [a is the acceleration=dv/dt]

hence we see that force not only depends on mass and acceleration but also on velocity and rate of change of mass. force f will depend on mass and acceleration only when mass is constant.

hence the statement that force is based upon mass and acceleration is false.

because if the tool that you are using is not balanced it there would be false mass.