# I Acceleration and force

1. Aug 1, 2017

### pranav p v

Consider a body of mass m at rest,then if I apply force f1 on that then it accelerates and attains a velocity of v1.then I remove that force..now the body is in uniform motion.if I apply a force f2 which is less than f1, then body will be accelerated or retardated?I know if same f1 is applied then acceleration will be the previous same value,and if I apply force greater than f1 then it will be accelerated ( but not uniform)..what about f2 less than f1

2. Aug 1, 2017

### phinds

Well, if you applied f2 in a direction opposite that of the body's motion, then yes it would be retarded/decelerated.

3. Aug 1, 2017

### CWatters

That depends on the direction of F2.

Yes. If you apply F1 again the acceleration will be the same a2 = a1.

If you apply a force F2 > F1 the object will accelerate faster so a2 > a1. However if the new force is constant the new acceleration will also be constant (=uniform).

If F2 < F1 the new acceleration will be less than before, a2 < a1

All you need to remember is Newton's Law...
F = ma
so
a = F/m

The fact that the mass is moving does not change law.

4. Aug 1, 2017

### Staff: Mentor

F=ma, period. It doesn't remember previous action and doesn't know anything about speed.

5. Aug 1, 2017

### vanhees71

Even more importantly $\vec{F}=m \vec{a}$, i.e., force and acceleration are both vectors!

6. Aug 1, 2017