What grade is the introduction of vector concept in middle school? Need to give chapters and corresponding text, to explain when the introduction of vector mathematics, physics.

What grade is the introduction of vector concept in middle school? Need to give chapters and corresponding text, to explain when the introduction of vector mathematics, physics.

It should be about the second grade of junior high school, when I learned speed in physics, it should be in the vector part in mathematics

"Is the magnitude of the force proportional to the acceleration product of the mass, or is the acceleration product of the mass proportional to the magnitude of the force
RT

According to Newton's second law, f = ma
We can see that both sides of the equal sign must be in direct proportion
Force is the cause of acceleration
So force is active
Then force is an independent variable
So it's the latter

An object with mass m can obtain an acceleration of magnitude a under the action of the resultant force F. in order to obtain an acceleration of magnitude 2a for an object, if its mass remains unchanged, the resultant force should be changed to zero___ F. If the resultant force is kept constant, its mass should be changed to zero___ m．

When the force F is applied, f = ma. If the acceleration is 2a, the applied force is f '= m × 2A = 2mA = 2F. If the force remains unchanged, the mass f = m ′× 2a, and the solution is m' = 12M, so the answer is: 2,12