Mechanics Flashcards
Define centroid with examples
center of mass of a geometrical figure having uniform density. eg. centroid of triangle is the intersection of 3 medians of triangle.
Define center of gravity with example
A point on an object where the distribution of weight is equal in all directions.
eg. center point of tennis ball
define equilibrium
When multiple forces act upon a body and it still remains at rest it is said to be equilibrium
define mechanical advantage & velocity ratio
ratio of the load (W) to the applied effort (P) used to lift the load.
the ratio of the distance traveled by the effort (y) to the corresponding distance traveled by the load (x)
Define load and effort
The weight to be lifted by a machine
The force applied on a simple lifting machine to lift the load
Define stress with its units
The applied force per unit cross-sectional area of a body is , measured in N/m² or Pa (Pascals).
Define strain with its units
change in dimension per unit original dimension
No unit
Define modulus of elasticity with units
Within the elastic limit the ratio of longitudinal stress to longitudinal strain is modulus of elasticity. N/m^2
Define modulus of rigidity with its unit
ratio of shear stress to shear strain. Pascal
Define bulk modulus with its unit
ratio of volume stress to volume strain
Define simple lifting machine and compound machine
a simple machine that can lift heavy loads by applying a comparatively smaller effort.
combination of 2 or more simple machines working together.
State relation between mechanical advantage velocity ratio and percentage efficiency
MA = VR / η
Define effort lost in friction
Energy or force wasted due to friction.
State the condition for reversibility of a machine
requires no energy losses.
Define friction and limiting force of friction
*It is a force that opposes the movement of an object.
*The maximum frictional force that prevents one body from sliding over another when an external force is applied
4 applications for centroid
*Indicates center of mass of a uniform solid
*Construction and engineering applications require stress and energy to ensure component stability.
*It is used to balance
-Balancing objects on a point
-balancing two people on sew-saw
*Centroids ensure balanced weight distribution and stability in machinery design.
lami’s theorem
It states that if 3 forces are acting on a point in a body and it remains in equilibrium each force is directly proportional to sine of angle b/w the other 2 forces.
P/sin = Q/sin =R/sin
define coefficient of fiction
Measure of surface slipperiness.
angle of repose
Max slope at which loose material remains stable without sliding.
State any two advantages and any two disadvantages of friction
ADV: *enables us to walk freely
* Breaks of vehicles work due to friction.
DISADV: *Mechanical energy is not conserved
*wear and tear
State Hooke’s Law
within the elastic limit stress is directly proportional to strain
State the types of axial stresses
Tensile stress, Volume stress and shear stress
Define resultant force
Single combined force from multiple forces acting on an object.
Distinguish between resultant and equilibrant
Resultant Force: Combined force from multiple forces.
Equilibrant Force: Balances out other forces
State law of moments.
Moment of a force: Sum of component moments
