# Law of inertia states roughly that an object will remain

1. Dec 29, 2011

### fonz

The law of inertia states roughly that an object will remain in it's current state of rest or motion unless acted upon by an external force.

So if for example I wanted to move a ball of mass m from stationary I would have to overcome the inertia.

Ok so if I wanted the ball to accelerate at some rate a then I would apply a force F equal to ma (F=ma)

The next few statements just seem embarrassingly naive but hopefully they will allow you to get an idea of the concept I am just not understanding

So if for example I want the ball to move at a constant velocity v then how much force do you need to apply?

From what I understand if I wanted the ball to reach v more quickly I just apply a greater force. Surely then if you apply a greater force yes the acceleration is greater therefore the desired velocity v is reached sooner but will it not just continue accelerating? How to you achieve constant velocity after applying a force?

What I need to happen is I apply some force to accelerate the ball at some rate a for it to reach v in some desired time but then v to remain constant how does this work?

I suppose what I am asking is if acceleration is the rate at which velocity is changing and in this case velocity is constant and the acceleration is equal to the force/mass of object but you want a to be zero and v to be constant therefore momentum is constant???

Hope this makes sense

Dan

2. Dec 29, 2011

### Gordianus

Re: Inertia

a) No force is needed to keep an obeject moving at constant velocity.
b) If you apply a constant force you get a constant acceleration and the speed grows linearly with time.Once you reach the desired speed the force should drop to zero .

3. Dec 29, 2011

### fonz

Re: Inertia

Ok so by example if the ball was 10kg the desired velocity was 10ms-1 in 1 second :

a=10ms-2
m=10kg

F=10x10 = 100N

So a force of 100N would have to be applied for 1s to reach 10ms-1 in 1 second correct?

4. Dec 29, 2011

### Gordianus

Re: Inertia

Yep.

5. Dec 29, 2011

### Ethan0718

Re: Inertia

The concept which you need to understand is that the "net" force acting on the body equals its mass times its acceleration.

6. Dec 29, 2011

### mrclynch

Re: Inertia

Think of it like this:
The only thing that any force is doing is exerting a push or a pull on something. When exerting a force on a body you are just giving it a push. The harder you push, the faster it will pick up speed. In essence, this is f=ma. The harder you push, the faster it will accelerate. If friction is negligible, the body will remain in constant linear motion after the force has been exerted. It will remain in constant motion (no acceleration) until other forces act upon it. After you have applied the force, you must stop applying it to achieve constant motion. The only thing that the force will do is cause an acceleration, which would cause the motion to be inconsistent.
I hope this helps.