# Difference between newtons 1st,2nd,and 3rd law? How to know when to use them on a tes

1. Dec 10, 2009

### slobodan48

1. The problem statement, all variables and given/known data
Can someone help me?

2. Relevant equations
Fg=mg
fnet=ma

3. The attempt at a solution
.
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Dec 10, 2009

### ideasrule

Re: Difference between newtons 1st,2nd,and 3rd law? How to know when to use them on a

Well, first, do you know what the laws ARE? If you do, it's pretty hard to not know the difference between them.

3. Dec 10, 2009

### kjohnson

Re: Difference between newtons 1st,2nd,and 3rd law? How to know when to use them on a

Newtons second law is the must common to see and is explained below:
F=ma which just states that the acceleration in a given direction is proportional to the NET force in that direction. If two or more forces act in a given direction find the resultant and that is the net force.

Newtons third law is also encountered and relates to interactions:
It states that every action has an equal and opposite reaction. Really this means that forces are equal and opposite at a boundary. If I push a block i will indeed accelerated it but that block pushes back on me with the same force. This is felt as resistance, the heavier the block I try to push the more force I feel.

Newtons first law just states that a object with mass will maintain its path (and velocity) until a force is applied on it. This applied force causes an acceleration. An acceleration is equal to (change in velocity)/(change in time). Likewise if there is no change in velocity there is no force acting on the object.

4. Dec 12, 2009

### stanton

Re: Difference between newtons 1st,2nd,and 3rd law? How to know when to use them on a

Newton's first law is 'all object will continue to be in their state of rest or of uniform speed in a straight line unless they are compelled to change that state by forces acting on them.'

Second law is 'the acceleration of an object is directly proportional to the net force acting on it and is inversely proportional to its mass. The direction of the acceleration is in the direction of the applied net force.'

The third law is 'Whenever one object exerts a force on a second object, the second exerts an equal and opposite force on the first.'