Modelling assumptions Flashcards
What 3 assumptions are made when the object is modelled as a particle?
- the mass of the object is concentrated at a single point
- rotational forces can be ignored
- air resistance can be ignored
What 3 assumptions can be made when an object is modelled as a rod?
- the mass is concentrated along a line
- no thickness
- rigid
What is a lamina?
An object with an area but negligible thickness (like paper)
What assumption can be made if an object is modelled as a lamina?
mass is distributed across a flat surface
What assumption can be made with a uniform body?
mass is concentrated at the centre of mass
What 2 assumptions can be made when an object is light?
- treat object as having zero mass
- tension is the same at both ends of a light string
What assumption can be made with an inextensible string?
acceleration is the same in both objects connected by a taut, inextensible string
What assumption can be made when a surface is smooth?
no friction between surface and any object on it
What assumption can be made when a surface is rough?
objects in contact with the surface experience a frictional force if they are moving or being acted on by a force
What assumption can be made with a wire?
it has one-dimension
What 2 assumptions can be made with a smooth and light pulley?
- pulley has no mass
- tension is the same on either side of the pulley
What 2 assumptions can be made with a bead?
- moves freely along wire or string
- tension is the same either side of the bead
What 2 assumptions can be made with a peg?
- dimensionless
- fixed
Air resistance is usually modelled as being __________.
negligible
What 3 assumptions can be made with gravity?
- all objects with mass are attracted towards the Earth
- Earth’s gravity is uniform and acts vertically downwards
- g is constant and is taken as 9.8 m/s2 (unless otherwise stated in the question)
What does it mean when an object is modelled as a particle? (1 mark)
The dimensions of the object are negligible.
What does it mean when an object is modelled as a rod? (1 mark)
All dimensions but one are negligible, like pole or beam
What does it mean when an object is modelled as a laminate? (1 mark)
The object has an area but negligible thickness, like paper.
What is meant by a ‘uniform body’? (1 mark)
The mass is distributed evenly.
What is meant by a ‘light object’? (1 mark)
The mass of the object is small in comparison with other masses, like a string/pulley.
What is meant by a ‘wire’? (1 mark)
A rigid thin length of metal.
What is the normal reaction? (2 marks)
The upward force that acts perpendicular to a surface when an object is in contact with the surface.
