When you add forces you get a single force?

Question

Trying to figure this out: the sum of Weight + Normal force = MA ??? huh?

Also N-W = MA?

Answer 1

This idea is known as the superposition principle of forces. This principle says that two forces acting on a body has the same effect as a single force equal to the sum of the individual forces. This works for any number of forces. This means that we can represent any number of forces as a single force (called the net force). Keep in mind that all of these forces are vectors.

In your example, the force of gravity (weight) + the normal force = ma.
This is only true if those are the only two forces acting on the object. Also, force and a (acceleration) are vectors.

Your other equation n - w = ma only deals with magnitudes since n and w point in different directions, you need to subtract one from the other. And as Madhukar said, they must be in exactly opposite directions from each other.

Answer 2

The resultant of forces will be a single force only if the lines of action of the forces are concurrent.

For non-concurrent forces, the resultant will be either a couple of forces or a couple associated with a single isolated force.

Couple of forces means two forces equal in magnitudes, opposite in direction and separated by a distance. Their equal magnitude multiplied by the distance between them gives the torque of a couple.

You have not fully described the situation where you are trying to understand weight + normal force = Ma. I can imagine such a situation in case of a roller coaster in its topmost position, where the normal force and weight are both in the downward directions and their sum is the centripetal force, Ma, where a is the centripetal acceleration.

Answer 3

By newton 2nd law,
resultant force = mass X acceleration

By Newton 1st law,
when an object is at rest, resultant force = 0
hence,
(+)weight + (-)normal = M x A
= 0N

Answer 4

this is centripetal force..
which equals to MA...
depends on the qn...



if i rmb correctly