Force = Mass x Acceleration
This equation is the basis for selecting sizing shakers and determining if your shaker can perform a specific shock or vibration test.
The premise is this: the more mass you put on your shaker, the less acceleration the shaker can produce. And vice-versa: the less mass you put on your shaker, the more acceleration it can produce. You may have noticed that all shakers have a force rating, and it’s exactly these ratings that determine what combination of mass and acceleration can be achieved on a given shaker.
But wait a second! Have you ever found that you cannot reach the maximum acceleration based on the shaker’s force rating and the calculated F=MA? As an example:
- I have a 500 kilogram force- shaker
- I want to perform a 5g sine test
- My max product mass is 100 kg (using M=F/A – 500 Kilogram force/5g)
- Run the test and any shaker can only reach 4.75g’s
It may seem that Force doesn’t always equal Mass x Acceleration. Why is this? The most common reason for this is due to the weight of the armature inside the shaker. When you add the weight of the armature and any other moving mass (such a driver bar when connecting a slip table to the armature), the maximum weight of your test item is reduced. The equation is correct, just remember to add up all of the moving masses.
Here are many software making these calculations automatically. Include many popular shaker models with their ratings pre-loaded for user convenience. Just enter the total moving mass and software calculates the maximum acceleration possible for a given test type
In the software we enter the Product mass, Armature mass and the software adds up a total moving mass automatically ( model vice specified already). With a shaker force of 500 -kilogram force the maximum acceleration is calculated.
Here we can see that the maximum acceleration is less than 5g’s because the total moving mass is (100+05, considering 5 kg mass of armature of selected shaker) 105 Kilogram force.
We now have to make a decision to either reduce our product mass or find a larger force rating shaker. If we reduce the product mass to 95 kilogram we can now reach our desired acceleration of 5g’s.