Module 3 - Section 2 - Mass, Weight And Centre Of Mass Flashcards
What is the mass of an object ?
And what’s it measured in ?
It is the amount of ‘stuff’ ( matter ) in in - its measured in kg
The greater the objects mass, the greater its resistance to…
A change in velocity ( called its inertia )
So the greater the mass of an object the greater its inertia - its tendency to stay motionless unless overcome by a resultant force
Whats happens to the mass of an object if the gravitational field strength changes ?
The mass of an object doesn’t change if the gravitational field strength changes - this is because mass is the amount of matter in an object and gravity doesn’t affect that - if the gravitational field strength changes then the weight changes
What is weight ? And what is it measured in ?
Weight is a fierce and its measured in Newtons like all forces
The equation for weight is w = mg
Gravity being 9.81Nkg*-1
Is mass a scalar or vector quantity ?
Mass is a scalar quantity
What is the centre of mass ( centre of gravity ) ?
The centre of mass of an object is the single point that you can consider its whole weight to act through - so for example a car - the centre of mass would be somewhere in the middle and this is where we consider its whole weight to act through i.e the force only acts through this one point
The object will also always balance around this point
What are the 2 ways of finding the centre of mass ?
By symmetry or by an experiment
How do you find the centre of mass by symmetry ?
The centre of mass for anything regular object is just at its centre - where the lines of symmetry will cross
Just draw the lines of symmetry and where they meet is the centre of mass
How do you find the centre of mass of an irregular object ?
Hang the object freely from a point ( e.g. one corner )
Draw a vertical line downwards from the point of suspension
Then hang the object from a different point and draw a line downwards from the suspension
The centre of mass is where the 2 lines cross
When will an object be stable ?
An object will be nice and stable if it has a low centre of mass and a wide base area - the bit that it lies on
The higher the centre of mass and the smaller the base area …
The less stable an object will be
When will an object topple over ?
An object will topple over if the vertical line drawn downwards from the centre of mass falls outside the base area - this is because of the moments around a pivot
