I have a question about gravity in dynamics

[IUIU]

Hi

I have a question about using gravity in dynamics...

first

In my thinking,,,

All force in dynamics is transferred by contact.

for example friction, tension, normal force,,,

but only except for gravity.

so I have always trouble in calculating gravity.....

In simple kinetics of parcicles

Newton's second law is

sum ( indivisual forces may be acting on the mass m)=m*a

I understand equation. but I have been confusing where I put gravity term.

Left or Right? ([indivisual] or [m*a])

In most problem about hanging problem, gravity term is in the Right.

but problem about car, gravity term is in the Left.

I don't know why this thing happen. ...

Help me please!

 

[tiny-tim]

Welcome to PF!

Hi IUIU! Welcome to PF!

In simple kinetics of parcicles

Newton's second law is

sum ( indivisual forces may be acting on the mass m)=m*a

I understand equation. but I have been confusing where I put gravity term.

Left or Right? ([indivisual] or [m*a])

In most problem about hanging problem, gravity term is in the Right.

but problem about car, gravity term is in the Left.

Gravity is a force, and so always goes on the left

(i'm assuming we're not talking about general relativity, where of course gravity isn't a force, it's an effect of the curvature of space-time)

… for example, a freely-falling body of mass m has only one force on it, mg, and the equation is mg = ma (so g = a)

… and a body stationary on a flat horizontal surface has two forces on it, mg and N, and the equation is mg - N = m*0 (so mg = N)

 

[IUIU]

oh thanks

I understand now ;;;

you saved me~~~

thank you