Mechanics Flashcards
(22 cards)
What is the acceleration equation?
acceleration = (final velocity - initial velocity) / time
On a displacement-time graph, how would you find:
- velocity?
- average speed?
- average velocity?
- gradient
- total distance / time
- total displacement / time
What does area represent on an acceleration-time graph?
Change in velocity
On a velocity-time graph, describe the motion of:
- positive straight line up
- horizontal straight line
- negative straight line above x axis
- constant acceleration
- constant velocity
- deceleration
On a velocity-time graph, describe the motion of:
- negative straight line under x axis
- line on x axis
- area under graph
- negative acceleration
- not moving
- change in displacement
What are the SUVAT equations?
- v = u + at
- s = 0.5(u + v)t
- s = ut + 0.5at^2
- s = vt - 0.5at^2
- v^2 = u^2 + 2as
Give the variable acceleration equations
v = ds/dt
a = dv/dt = d^2s/dt^2
To go from a to v to s, integrate instead of differentiate
What does the coefficient of friction, u, measure?
What does its value indicate?
The level of roughness of a surface.
If u = 0, the surface is smooth. u can be larger than 1, but often is between 0 and 1
What is the equation for maximum friction?
When does this occur?
Fr = uR
where Fr = friction, u = coefficient of friction, R = normal reaction
This occurs when the particle is moving, or on the point of moving
What is the equation for friction when the object is not at the point of moving?
Fr <= uR
What is the equation of a moment?
Moment = force x distance
How should you change your moments calculation if it is on the point of tilting?
The pivot without the weight applied is removed from the equation
What does it mean if a rod is uniform?
The weight acts from the centre
What is the equation for weight?
Weight = mass x gravity
Give some generic modelling assumptions
- All forces acting on the object act on the centre of mass (so have no spinning effect)
- Air resistance is negligible / constant
- Objects modelled as a particle are assumed to have no size
What is Newton’s second law?
F = ma
What is Newton’s third law?
For two objects, A and B, in contact with each other, the force exerted on A by B is equal in magnitude but opposite in direction by the force exerted on B by A.
What do the modelling assumptions of a string connecting two particles?
- Light = tension is the same throughout the length of the string and mass is negligible
- Inextensible = acceleration of the masses is the same
- String is horizontal / vertical = force acts in only that direction
What direction is a negative moment (conventionally), and vice versa?
Negative moments are clockwise, positive moments are anticlockwise
What is a lamina?
An object which can be modelled as a plane area with mass but negligible thickness
What does it mean if a rod is ‘about to tilt’ around a point?
Any normal reactions acting at any other supports along the rod will be zero. The tension in any strings supporting the rod at any other points will be zero
What does it mean if an object is non-uniform?
The centre of mass could be at any point on the object
