A muscle cramp is a sudden, painful contraction of a muscle, during which movement is difficult. What is happening at the cellular level during a muscle cramp?
OA
The proteins in the myofibrils become denatured, preventing relaxation.
B.
Myosin and actin do not fully detach, so the muscle cannot relax.
O C.
The motor neuron does not send a signal, so the muscle cannot relax.
OD
A lack of calcium causes the sarcomeres to lock together, preventing relaxation.

grav forces affect all objects magnetic forces affect magnetic objects and electric currents

air exerts forces on falling objects near earth’s surface.

explanation:

the term 'free falls' refer to object that are falling towards the earth, in a situation in which gravity is the only force acting on the object.

for an object in free fall, the acceleration is constant (g, the gravitational acceleration), and so the velocity of the object constantly increases.

for objects near earth's surface, there is always another force acting on the object: the resistance due to the air. this force is opposed to the direction of fall of the object, and it is proportional to the velocity of the object, so as the object falls down, this force increases up to a point when it balances the force of gravity, and the object continues its motion at constant velocity (called terminal velocity). since in this case gravity is not the only force acting on the object, we are not in a situation of free fall.