Mechanics Definitions

Question 1

Vector

Answer 1

Both magnitude and direction.
Displacement, force, velocity, momentum & acceleration.

Question 2

Scalar

Answer 2

Only has a magnitude.
Distance, speed, power, energy, mass & time.

Question 3

Resultant force

Answer 3

The single equivalent force that can be used to represent all of the other forces acting in a system to simplify analysis.

Question 4

Co-planar

Answer 4

all exists on the same plane (2 dimensional)

Question 5

Concurrent

Answer 5

all forces act through a current point

Question 6

Equilibrium

Answer 6

There is no resultant force, no acceleration. Therefore (according to Newton’s 1st Law), the object will remain stationary or moving at a constant velocity.

Question 7

What are the conditions of equilibrium of co-planar forces acting on a point?

Answer 7

1 - the total resultant force is zero/adding the components equals zero.
2 - if the forces are added together, they will form a closed triangle.

Question 8

Free-Body Diagram

Answer 8

Used to show the forces acting on a point, arrows must start at a point where the force is acting. WEIGHT is the force due to gravity and must act from the centre of gravity.

Question 9

Centre of Gravity

Answer 9

a point from which the weight of the system may be considered to act

Question 10

Centre of Mass

Answer 10

a point in a body around which the resultant torque (moment) due to the pull of gravity is zero

Question 11

Orthoganal

Answer 11

at right angles

Question 12

Moment Equation

Answer 12

Force x Perpendicular Distance Between the Line of Action of the Force and the Pivot

Question 13

Couple

Answer 13

a pair of co-planar forces where the two forces are equal in magnitude but act in opposite directions

Question 14

Moment of a Couple Equation

Answer 14

Force x Perpendicular Distance Between Lines of Action of Forces

Question 15

Negligible Mass

Answer 15

ignore mass

Question 16

Uniform Mass

Answer 16

mass acts at the centre of the object

Question 17

Principle of Moments

Answer 17

In equilibrium, the sum of the clockwise moments about a point equals the sum of the anti-clockwise moments.

Question 18

Principle of Equilbrium

Answer 18

1 - The total resultant force is zero.
2 - Resultant moment about any point is zero.

Question 19

Unstable Equilibrium

Answer 19

The centre of mass can move easily beyond the pivot point and continue turning when the force is removed, to make things more stable. (Tilt or topple?)

Question 20

Stable Equilibrium in a Glass Bottle

Answer 20

Wide base, low centre of mass.
Difficult to push over.
When a small force is applied and removed, the bottle will return to its original position (TILT).

Question 21

Unstable Equilibrium in a Glass Bottle

Answer 21

Narrow base, high centre of mass. Easy to push over.

Question 22

The process when an object topples over.

Answer 22

A force is applied, and the weight produces a clockwise turning moment about the pivot. As the block tilts farther, the line of action of the force passes through the pivot (unstable equilibrium). The line of action of weight is outside of the base are, and the weight produces an anticlockwise moment about the pivot - toppling it over.