Mechanics Flashcards
What is a vector?
A quantity which had both magnitude and direction
What is a scalar?
A scalar quantity had a magnitude only
State what is means by the following modelling assumption: Particle
And state what the term means
Dimensions of the object are negligible
1) Mass of the object is concentrated at a single point
2) Rotational forces and air resistance can be ignored
State what is means by the following modelling assumption: Rod
And state what the term means
All dimensions but one are negligible
1) Mass is concentrated along a line
2) No thickness
3) Rigid
State what is means by the following modelling assumption: Lamina
And state what the term means
Object with area but negligible thickness
1) Mass is distributed across a flat surface
State what is means by the following modelling assumption: Uniform body
And state what the term means
Mass is distributed evenly
1) Mass of the object is concentrated at a single point at the geometrical centre of the body (centre of mass)
State what is means by the following modelling assumption: Light object
And state what the term means
Mass of the object is small compared to other masses
1) Treat object as having 0 mass
2) Tension the same at both ends of a light string
State what is means by the following modelling assumption: Inextensible string
And state what the term means
A string that does not stretch under load
1) Acceleration is the dame in objects connected by a taut inextensible string
State what is means by the following modelling assumption: Smooth surface
1) Assume that there is no friction between the surface and any object on it
State what is means by the following modelling assumption: Rough surface
And state what the term means
If a surface is not smooth
1) Objects in contact with the surface experience a frictional force if they are moving or are acted on by a force
State what is means by the following modelling assumption: Wire
And state what the term means
Rigid thin length of metal
1) Treated as one dimensional
State what is means by the following modelling assumption: Smooth and light pulley
1) Pulley has no mass
2) Tension is the same on either side of the pulley
State what is means by the following modelling assumption: Bead
And state what the term means
Particle with a hole in it for threading on a wire or string
1) Moves freely along wire/string
2) Tension is the same on either side of the bead
State what is means by the following modelling assumption: Peg
And state what the term means
A support from which a body can be suspended or rested
1) Dimensionless and fixed
2) Can be rough or smooth as specified
State what is means by the following modelling assumption: Air resistance
And state what the term means
Resistance experienced as an object moves through air
1) Usually modelled as being negligible
State what is means by the following modelling assumption: Gravity
And state what the term means
Force of attraction between all objects
1) Assume that all objects with mass are attracted towards the Earth
2) Earth’s gravity is uniform and acts vertically downwards
3) g is constant and is taken as 9.8 m/s²
Define velocity
Rate of change of displacement
Average velocity =
Displacement from starting point / Time taken
Average speed =
Total distance travelled / Time taken
Define acceleration
The rate of change of velocity
What is the constant acceleration equation with s, u, v and t in it?
s = ((u + v)/2)t
What is Newton’s First Law of motion?
An object at rest will stay at rest and that an object moving with constant velocity will continue to move with constant velocity unless an unbalanced force acts on the object
What will a resultant force on an object cause?
Will cause the object to accelerate in the same direction as the resultant force
What is Newton’s second law?
The force needed to accelerate a particle is equal to the product of the mass of the particle and the acceleration produced. F = ma
What is Newton’s third law?
For every action there is an equal and opposite reaction
Describe the forces if a rigid body is on the point of tilting
The reaction at any other support (or the tension in any other wire/string) is zero
When is a particle/rigid body in static equilibrium?
If it is at rest and the resultant force acting on the particle is zero
Describe what is true for a body in static equilibrium:
1) The body is stationary
2) The resultant force is zero
3) The resultant moment is zero
