Effect of acceleration on a mass
Ive got a query which im thinking should be simple but I cant for the life of me think how to solve it.
I have a mass of 500 kg resting on a beam. It is subjected to vibration of 2m/s2 directly down, how would I calculate the extra force subjected on the beam due to this acceleration?
Is it as simple as working out the force of the mass while stationary then working out the force applied due to acceleration (m*a) and then adding them together?
I have a mass of 500 kg resting on a beam. It is subjected to vibration of 2m/s2 directly down, how would I calculate the extra force subjected on the beam due to this acceleration?
Is it as simple as working out the force of the mass while stationary then working out the force applied due to acceleration (m*a) and then adding them together?
Original post by Diggedy
Ive got a query which im thinking should be simple but I cant for the life of me think how to solve it.
I have a mass of 500 kg resting on a beam. It is subjected to vibration of 2m/s2 directly down, how would I calculate the extra force subjected on the beam due to this acceleration?
Is it as simple as working out the force of the mass while stationary then working out the force applied due to acceleration (m*a) and then adding them together?
I have a mass of 500 kg resting on a beam. It is subjected to vibration of 2m/s2 directly down, how would I calculate the extra force subjected on the beam due to this acceleration?
Is it as simple as working out the force of the mass while stationary then working out the force applied due to acceleration (m*a) and then adding them together?
No, unfortunately not that simple.
You need to provide a little more background.
Firstly, what is causing the mass to vibrate?
Is there another "driving" force acting on it?
Is this mass performing simple harmonic motion?
What exactly do you mean by a downwards vibration of 2m/s/s?
Is the vibration the result of the elasticity in the beam?
Sorry to sound so nit-picky, but in order to give a meaningful answer you need to provide more information.
To do the physics you need to consider the forces acting on the mass causing its motion, one of which is coming from the beam, and the Newton's 3rd Law reaction to that force.
Acceleration is the result of a force.
It's the wrong way to start the solution by thinking of "the result of acceleration" in this case.
(edited 9 years ago)
Thanks for the reply.
Load is attached to bracket (simple cantilever beam) which is attached to moving machinery. The machine used to be stationary so the load calcs for the bracket were just based on the weight of the mass. This has now changed and when the machine moves along the ground it bounces which creates a vibration of 2m/s2 in the vertical axis. (measured with an accelerometer).
I want to know what the new load is acting on the bracket due to this vibration
Load is attached to bracket (simple cantilever beam) which is attached to moving machinery. The machine used to be stationary so the load calcs for the bracket were just based on the weight of the mass. This has now changed and when the machine moves along the ground it bounces which creates a vibration of 2m/s2 in the vertical axis. (measured with an accelerometer).
I want to know what the new load is acting on the bracket due to this vibration
Isn't this, in the simplest case, the same problem as the person standing in a lift with the lift (and person) accelerating downwards at 2m/s/s?
What is the force of the lift floor on the person (mass 500kg!) in this case. This is also the force of the person on the lift floor.
By the way, if this is a vibration, then the person and lift also move upward at 2m/s/s.
What is the force now?
By the way.
Over one complete vibration the mean value of the force must equal the weight of the person.
At some points it is greater and at others it is less.
Somehow I think there is more to this and I don't want to trivialise the problem.
The beam has elasticity and the mass on it will surely vibrate with some sort of oscillatory motion?
It's acceleration will surely not be constant at 2m/s/s. I imagine that to be a peak value. It will also not be exclusively downwards. In fact, the beam will need to provide a greater force on the mass to accelerate it upwards, will it not? Assuming the only two forces on the mass are its weight and that of the beam.
What is the force of the lift floor on the person (mass 500kg!) in this case. This is also the force of the person on the lift floor.
By the way, if this is a vibration, then the person and lift also move upward at 2m/s/s.
What is the force now?
By the way.
Over one complete vibration the mean value of the force must equal the weight of the person.
At some points it is greater and at others it is less.
Somehow I think there is more to this and I don't want to trivialise the problem.
The beam has elasticity and the mass on it will surely vibrate with some sort of oscillatory motion?
It's acceleration will surely not be constant at 2m/s/s. I imagine that to be a peak value. It will also not be exclusively downwards. In fact, the beam will need to provide a greater force on the mass to accelerate it upwards, will it not? Assuming the only two forces on the mass are its weight and that of the beam.
(edited 9 years ago)
Your right there is more to it but I think to determine the elasticity of the beam would be difficult as its actually a fabricated steel bracket. I am treating it as a simple beam as the end result is FEA analysis using software, I just need to be somewhere in the region. . I did consider it to be the same as the lift scenario but I was figuring, like your pointing out that maybe that is too simple. My end result after the FEA analysis will be to prove the software result with the use of strain gauges so I dont want to over complicate the problem, but I dont want to be too general all the same. Perhaps I should have explained my end goal in the first post, i apologise for the vagueness.
Your also right about the peak, the peak is actually 2m/s2, the average is slightly lower but I want to use the worst case for my analysis.
Your also right about the peak, the peak is actually 2m/s2, the average is slightly lower but I want to use the worst case for my analysis.
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