Which two conditions must exist in order for radiation to occur?
the presence of a solid, liquid, or gas and a temperature difference
direct contact of molecules and the presence of a solid, liguld, or gas
the presence of electromagnetic waves and direct contact of molecules
e a temperature difference and the presence of electromagnetic waves

f is prop to m1xm2 double m1 double force

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.