How can you tell, based on observing an object, that there is a net force acting upon that object?

Net force is the sum of all forces acting on an object. The net force can be calculated using Newton's second law, which states that F = ma, where: F is the net force. m is the mass of the object.

Explanation:

accelerating

Explanation:

If  accelerating it has a net ( unbalanced) force acting on it .

  with zero net forces it will either remain at rest or continue moving (but not accelerate)

atomic = no of protons.

mass number-atomic number = neutron number

there is no correct list among the choices you've provided.

the list might look something like this:

-- baby human

-- piccolo

-- flute

-- soprano singer

-- trumpet

-- tenor singer

-- trombone

-- baritone singer

-- baritone horn

-- bass singer

-- tuba

since i had to make up the list myself, i made it easy on myself, and i didn't try to shuffle the string instruments and woodwinds into it too.