Topic 4: forces/density/pressure

Question 1

Define center of gravity

Answer 1

a point where the entire weight of the object seems to act.

Question 2

Define center of mass

Answer 2

a point where the entire mass of the object seems to be concentrated.

Question 3

Define both center of mass and center of gravity

Answer 3

the point through which a single force has no turning effect on the body.

Question 4

define moment

Answer 4

the turning effect of a force

Question 5

what is the equation for moment

Answer 5

moment = force x perpendicular distance between pivot and line of action of force

Question 6

What are the units for moment

Answer 6

Newton meters, Nm

Question 7

What is a couple

Answer 7

a pair of forces. same magnitude but opposite directions. parallel but not along the same line. cause a rotation.

Question 8

What is the torque of a couple

Answer 8

the turning force produced by the couple.

Question 9

what is the equation for the moment (torque) of a couple

Answer 9

moment = force x perpendicular distance between lines of action.

Question 10

what is the principle of moments

Answer 10

total clockwise moments about a point are equal to the total anti-clockwise moments about the same point.

Question 11

What does it mean when an object is in equilibrium

Answer 11

no net force and no net moment acting on the body. the forces and moments are balanced.