Unit v friction and rigid body dynamics

GE 8292 ENGINEERING MECHANICS

1. UNI T V-Friction and Element of Rigid Body Dynamics
1. What is angle of repose?
The angle of the inclined plane, at which the body tends to slide down is known as angle
of repose.

2. Define co efficient of friction and limiting friction.
It is defined as the ratio of limiting friction to the normal reaction. It is denoted by µ.

µ= (limiting friction/Normal reaction) = (F/N)
The maximum value of frictional force, which comes to play, when a body just tends
to move, is known as limiting friction.
3. State coulomb’s law of dry friction or state the law of dry friction.

1. The frictional force always acts in a direction opposite to that in which the body tends
to move.
2. The limiting frictional force bears a constant ratio to the normal reaction between
the two surfaces.
3. The frictional force depends up on the roughness/smoothness of the surfaces.
4. The frictional force is independent of the area and the shape of the contacting
surfaces.
4. Define static and dynamic friction.
Static friction is the friction experienced by a body during rest.
Dynamic friction is the friction experienced by a body during motion.
5. Define angle of friction.
The angle between the resultant R and the normal reaction N is called angle of friction.
It is denoted by the symbol ɸ.
µ=tanɸ
6. What you understand by dry friction?
When the two surfaces in contact are dry and there is no lubrication and resisting
force acts opposite to the tendency of motion, then the friction is called dry friction.
7. Give the causes of rolling resistance.
When one body is made to roll freely over a body, a resistance is developed in the
opposite direction known as rolling resistance. This resistance helps to roll the body without
any slipping or turning of the body.

2. 8. What is general plane motion?
If the particles move in parallel planes and motion is neither nor is translation, then
the motion referred to as general plane motion.
9. Define the angular acceleration of rigid body.
The rate of change of angular velocity per unit time is called angular acceleration.
10. What is meant by instantaneous axis of rotation?
At any given instant, the velocities of various particles of a body, such as slab, are the
same if it is rotating about a certain axis perpendicular to the plane of the slab. This axis is called
the instantaneous axis of rotation.
10. What is meant by instantaneous Centre of rotation?
The instantaneous axis intersects the pane of the body at a point of called
instantaneous Centre of rotation.
11. What is meant by impact?
A collision between two bodies, which occurs in a small interval of time, during which
the two bodies exert on each other a relatively large force, is called impact.
12. What are the different types of motion of rigid body?
1. Translation. (Rectilinear and curvilinear motion)
2. Rotation about a fixed axis.
3. General plane motion.