Introduction to mechanics (7)

Question 1

Force

Answer 1

a push or a pull. Can be contact (exerted between bodies that touch each other) or non-contact (exerted over a distance by gravitational, electric and magnetic fields).

Question 2

Turning moment (torque)

Answer 2

the size of a turning effect. The force × perpendicular distance from the pivot. The unit of a moment is Nm or Ncm.

Question 3

Scalar quantity

Answer 3

one which has magnitude only.

Question 4

Vector quantity

Answer 4

one which has magnitude and direction.

Question 5

Resultant vector

Answer 5

the vector that results from adding two or more vectors in a vector sum (e.g. resultant force or resultant displacement).

Question 6

Pivot

Answer 6

the point about which an object rotates.

Question 7

Equilibrium

Answer 7

an object is in equilibrium, when the sum of the forces = 0 and the sum of the turning moments = 0.

Question 8

Centre of mass

Answer 8

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

Question 9

Couple

Answer 9

a pair of forces that provide a turning effect but no translational movement. They act in opposite directions, are parallel, but do not act along the same line.