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Author Topic: Force = m x a and F = P x A. Difference?  (Read 312 times)

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Offline jigarmech

Force = m x a and F = P x A. Difference?
« on: December 26, 2017, 09:32:34 PM »
Can i use value of F = m x a in F = P x A?
"A neutron walks into a bar and asks how much for a drink, the barman replies for you NO CHARGE"

Offline jigarmech

Re: Force = m x a and F = P x A. Difference?
« Reply #1 on: December 26, 2017, 10:04:46 PM »
This is more of a physics question and not an mechanical engineering question.  :-\\
"A neutron walks into a bar and asks how much for a drink, the barman replies for you NO CHARGE"

Offline nethan

Re: Force = m x a and F = P x A. Difference?
« Reply #2 on: December 26, 2017, 10:54:11 PM »
 :111: in what context you're saying? can you elaborate?
“The greatest challenge in life is discovering who you are, The second greatest is being happy with what you find.”
― Auliq Ice

Offline jigarmech

Re: Force = m x a and F = P x A. Difference?
« Reply #3 on: December 26, 2017, 11:40:20 PM »
:111: in what context you're saying? can you elaborate?

i am solving a problem where my weight of ball needed is calculated with the help of F = P x A formula, weight is the counter force that will act against pressure to keep my ball in stable condition. If i am suppose to lift the ball, my pressure should be high as compared to the stable condition pressure. So i applied more pressure and found the force that is applied on the ball due to that pressure for same weight of the ball that was taken for stable condition.
Applying same force condition to find acceleration of the ball in equation F = m x a, will it give me result? :(
"A neutron walks into a bar and asks how much for a drink, the barman replies for you NO CHARGE"

Offline susovan

Re: Force = m x a and F = P x A. Difference?
« Reply #4 on: December 27, 2017, 04:02:17 PM »
The force acting in the case is the thrust upwards and the weight of pallet downwards. Weight is force due  to gravity and can be calculated by  multiplying the mass  X 9.8.

The resultant force on each pallet can be derived by
R = Thrust - weight.

Acceleration the speed increases each second. It can be calculated using the equation.

Accleartion = resultant force ( Newton ) / mass (kg).

Suppose your pallet weight is 50 grams and the thrust or force is 5N for 1 sec.
To find weight 50 gms needs to be changed to kg ( devided by 1000kg ). This gives mass of 0.050kg. 
Weight is mass X 9.8 = 0.49 N

The resultant force is the thrust - Weight :  5 N - 0.49 = 4.51N.

Acceleration = resultant force devided by mass = 4.51 / 0.050 = 90m/ s.  :021:

Offline nethan

Re: Force = m x a and F = P x A. Difference?
« Reply #5 on: December 28, 2017, 10:00:13 PM »
:111: in what context you're saying? can you elaborate?

i am solving a problem where my weight of ball needed is calculated with the help of F = P x A formula, weight is the counter force that will act against pressure to keep my ball in stable condition. If i am suppose to lift the ball, my pressure should be high as compared to the stable condition pressure. So i applied more pressure and found the force that is applied on the ball due to that pressure for same weight of the ball that was taken for stable condition.
Applying same force condition to find acceleration of the ball in equation F = m x a, will it give me result? :(
Okay. Let me make it simple for you. Remember to ALWAYS look at the units of these two equations.
Let me do it for you.
Two cases:
1. F = m*a
2. F = P*A
Case 1. Force is mass times acceleration
Mass = Kg
Acceleration = m/s2
Hence F = kg*m/s2

Case 2. Force is Pressure times Area
Pressure = kg/m2(for your case only, as you are neglecting gravitational acceleration to find minimum weight of the ball for applied pressure. Otherwise it will be kg/(m*s2) -hope you understood my point.
Area = m2
Hence F = kg

Comparing case 1 and case 2, you will find additional m/s2 in case 1.
In case 1, unit of F is kilogram-force. Take a look at the wiki hyperlink to understand what Kgf is.
You cannot directly use the value of Force = P*A into Force = m*a unless you multiply it by acceleration.
« Last Edit: December 28, 2017, 10:07:02 PM by nethan »
“The greatest challenge in life is discovering who you are, The second greatest is being happy with what you find.”
― Auliq Ice

Offline jigarmech

Re: Force = m x a and F = P x A. Difference?
« Reply #6 on: December 29, 2017, 10:26:40 AM »
thanks @susovan and @nethan
"A neutron walks into a bar and asks how much for a drink, the barman replies for you NO CHARGE"

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