Centre of Mass/Equilibrium Flashcards
Define the CoM.
A conceptual point, where all the mass of the body can be considered to be concentrated.
How would someone find the CoM of an object?
Evenly compress the mass down until you reach a common point.
If a resultant force pushes an object, about what point will it rotate?
If the resultant force is not through the objects CoM, then it will rotate about its CoM.
Define Gravity.
Gravity is a force acting between masses. It is always attractive and depends on the masses involved in their separation.
In a uniform gravitational field, what relationship will the CoM and CoG have?
CoM and CoG will coincide.
How is the CoG calculated for geometric shapes?
CoM can be calculated as we know the distribution of all the points making it up.
Find the midpoint of all these points collectively to calculate CoG.
How is the CoG calculated for rigid bodies (e.g. not geometric shapes)?
The balance/knife edge method.
CoG is directly above the point of support.
It is unethical to put a human on a knife edge
What are the 2 main rules that apply when a system is in equilibrium?
- The sum of the forces on the body are zero.
2. The sum of the moments about a point are zero.
What is a moment/torque (in literal terms)?
The product of a force and the perpendicular distance from the line of action of the force, to the pivot point.
What equation is used to calculate a moment/torque?
Moment = Force x Perpendicular Distance
If a force is pushing into the pivot point, how much rotational movement will occur?
None.
In terms of moments, is the clockwise motion negative or positive?
Negative.
Measured in Nm.
In terms of moments, is the anticlockwise motion negative or positive?
Positive.
Measured in Nm.
What is a statograph?
A device used for finding the CoG by summing moments about one axis (like a seesaw).
Individual lies on the statograph with their head at the scale end and feet at the pivot end.
A reaction board will sum the moments about how many axis to find CoG?
2
