Dynamics

Question 1

What is kinematics?

Answer 1

Study of the geometry of motion alone.

Question 2

What is kinetics?

Answer 2

Study of the unbalanced forces that act to alter the motion.

Question 3

What is the kinetics of particles?

Answer 3

When all of the applied forces are concurrent through the centre of mass, there will be no rotation and the object may be treated as a particle.

Question 4

What is mass?

Answer 4

a measure of an object’s reluctance to accelerate

Question 5

What is the direct application of Newton II?

Answer 5

Since a particle will accelerate only in the direction of the unbalanced applied force, we may apply the law separately in each orthogonal component direction (x,y or n,t) as they will not interact.

Question 6

What is momentum?

Answer 6

the unbalanced force equals the rate of change of momentum.

Question 7

What is the work energy method?

Answer 7

Only the tangential force component (n-t coordinates) does work on a particle.

Question 8

What is a conservative force?

Answer 8

The work done by a weight force is independent of the path taken

Question 9

What is gravitational potential energy?

Answer 9

The gravitational potential energy of a particle of mass m is the negative of the work done against the gravitational field to elevate the particle a distance h above some arbitrary reference plane

Question 10

What is elastic potential energy?

Answer 10

Elastic potential energy is stored within an elastic element, such as a spring, when work is done on that spring by either an extension or compression force. The work may be recovered during the spring’s release. The elastic force is a conservative force.

Question 11

What is the law of conservation of dynamical energy?

Answer 11

Where the only forces are elastic, gravitational and “non-working” constraint forces, the term U will be zero and the energy expression becomes ∆E = 0 , which is the law of conservation of dynamical energy.

Question 12

What is rectilinear translation?

Answer 12

every point on the body moves in parallel straight lines, nor does any line attached to the object rotate. Describing the kinematics of any point on the object completely defines the motion of every point.

Question 13

What is curvilinear translation?

Answer 13

every point on the body moves on congruent curves, and any line attached to the object does not rotate. Describing the kinematics of any point on the object completely defines the motion of every point.

Question 14

What is fixed axis rotation?

Answer 14

every point on the body moves on a circular path about a fixed axis. The angular motion kinematic equations are analogous to those of rectilinear motion. Angular displacement = θ in radians.

Question 15

What is the General Plane Motion?

Answer 15

the object executes a combination of translation and rotation. All lines on a rigid object, lying in its plane of motion, have the same ∆θ, ω and α.

Question 16

What is the mass centre? (3)

Answer 16

When the line of action of an unbalanced force acts through the mass centre, translational acceleration only will result, i.e. no rotational acceleration.

Alternatively, the mass centre is that point about which an object will rotate when subject to a (pure) applied couple. i.e. the mass centre will remain stationary while all other points orbit about it with circular motion.

For translational acceleration purposes, all of the mass may be considered to be concentrated at the mass centre, often designated as G.

Question 17

What is a moment of inertia?

Answer 17

is a measure of reluctance of an object to accelerate angularly. It is dependent on the distribution of mass about the axis of rotation

Question 18

What is the significance of the centred area of the beam’s cross section?

Answer 18

centroid area is a neutral axis (strain from bending is 0)

Question 19

What is the significance of the second moment of area of the beam’s cross section about the neutral axis?

Answer 19

A beam’s resistance to bending is related to I

Question 20

What is the difference between gauge pressure and absolute pressure?

Answer 20

absolute pressure is = gauge pressure + atmospheric pressure

Question 21

Explain why the bottom of the submarine experiences a force and state in which direction it acts.

Answer 21

Pressure at a point acts in all directions within a fluid and perpendicular with any solid surface in contact with the fluid.

Question 22

Why is there a force experienced by the pipe bend? (2)

Answer 22

pipe applies force to change direction of fluid

must be an equal or opposite reaction of force on the pipe