# F=ma proof and understanding force

1. Apr 19, 2005

### chandran

general
force is a push or pull.

how this push or pull is equal to mass x acceleration.

one more doubt.

a ball is released from rest from the top of a building. initial velocity=0.after 1sec velocity is 9.81m/sec. so acceleration is 9.81m/sqs. so force
that caused the ball to fall from 0 to 1sec is 9.81N considering the mass to be 1kg. from 1second to 2seconds the net force is another 9.81N.
am i correct in the above statements.

Can anybody clarity on force on statics theory and the force referred in dynamics theory.

2. Apr 19, 2005

### dextercioby

Let me put in my dear terms.Technical ones.

In the Newtonian formulation of classical mechanics,the second postulate (which is valid in inertial reference frames) says that,for a mechanical system undergoing translation movement (a system of point masses):

$$\frac{d\vec{p}}{dt}=\sum_{k}\vec{F}_{k}$$

,where $\vec{p}$ is the total momentum of the system and $\vec{F}_{k}$ are the internal & external forces...

So u can "prove" that
$$\vec{F}=m\vec{a}$$

,starting with the II-nd axiom & simplifying hypothesis...

Daniel.

P.S.That acceleration is $\left|\vec{g}\right|=9.80665 \ \mbox{ms}^{-2}$

3. Apr 20, 2005

### Staff: Mentor

All correct. Ignoring air resistance, the only force on a falling body is that due to gravity, its weight.

Can you restate your question? Whether or not a problem is one of statics or dynamics depends on whether the net force on an object is zero. Zero or not, forces are treated the same way.

4. May 10, 2006

### RipClaw

Well,

I too want to understand the concept of "force".
I find it a bit hard to understand.

1> I don't need proofs. I just need the understanding.
2> Is 'time' a part of 'force' ?? . Can we talk about force ignoring time ?

5. May 10, 2006

### Hootenanny

Staff Emeritus
A force is anything that causes a body to change it's velocity. One can talk about a force acting without reference, however, one cannot define force without reference to time. Essentially unless a body is in equilibrium (no net force), it is not meaningful to talk about force without reference to time.

See this; http://en.wikipedia.org/wiki/Force

~H

6. May 10, 2006

### JohnSimpson

if a body changes its velocity (momentum), a force has been exerted