Question

Question #52385

Answer 1

Newton's first law says that an object will stay at rest or travel at constant velocity if no resultant force acts upon it.

Newton's second law states that `F=(mv-"mu")/t=(m(v-u))/t=ma`

If we rearrange the equation, we get `a=F/m`, where `F` is the resultant force, if the net force (total force) acting on a body is 0, then `F=0`. So, `a=0/"mass"=0`, no acceleration. An object at rest or constant velocity has no acceleration.

Answer 2

Newton's second law states that:

`"Force"` `=` `"mass"` `xx` `"acceleration"`

Mass must be nonzero. Therefore:

If the Force is 0, the Acceleration must also be 0.

If the Force is non-zero, the Acceleration must also be non-zero.

So what we're saying is that if the force is 0, then the acceleration must also be 0; and if the acceleration is nonzero, then the force must also be nonzero.

If the acceleration is 0, then there is no change in the object's motion, since acceleration is (by definition) a change in motion.

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Using this notion of acceleration, we can change our previous statement to this:

If there is a net force of `0` on the object, there is no change in motion. If the net force is NOT `0`, then the object will change its motion.

Notice that this is exactly what Newton's first law states, but written in a slightly different way:

An object's motion will not change unless there is an unbalanced (nonzero) force acting on it.