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What are the factors that affect the size of a moment?
force and the perpendicular distance
State the principle of moments for an object in equilibrium
the sum of clockwise moments equals the sum of anticlockwise moments
Explain what is meant by the perpendicular distance
distance between the pivot and the line of action of the force
A force of 10 N is applied perpendicularly to a door at a distance of 0.5 m from the hinges. Calculate the moment.
Moment = 10 N × 0.5 m = 5 Nm
To turn a nut, a moment of 15 Nm is needed. What force must be applied at the end of a 0.3 m long spanner?
Force = Moment / Distance = 15 Nm / 0.3 m = 50 N
A force of 50 N creates a moment of 10 Nm. Calculate the perpendicular distance from the pivot
Distance = Moment / Force = 10 Nm / 50 N = 0.2 m
Two children are on a seesaw. Child A (400 N) sits 1.5 m from the pivot. Calculate the moment created by Child A.
Moment = 400 N × 1.5 m = 600 Nm (anticlockwise)
Two children are on a seesaw. Child A (400 N) sits 1.5 m from the pivot. Child B (300 N) sitting on the other side. How far must Child B sit from the pivot for the seesaw to be equilibirum?
Moment A = Moment B. 600 Nm = 300 N × d; d = 600 Nm / 300 N = 2m
A mechanic applies a force of 100 N perpendicular to a 0.5 m long wrench. What is the moment?
Moment = 100 N × 0.5 m = 50 Nm
A moment of 12 Nm is required to open a window. If you push with a force of 30 N, how far from the pivot must you apply this force?
Distance = Moment / Force = 12 Nm / 30 N = 0.4 m
A mechanic applies a force of 100 N perpendicular to a 0.5 m long wrench. If the mechanic used another 1 m long wrench, what force would be needed to create the same moment like 0.5 m wrench?
Moment / Distance = 50 Nm / 1 m = 50 N
Calculate the moment created by a 200 N force acting at a perpendicular distance of 25 cm from a pivot
50 Nm
A door is 0.8 m wide. If you push at the very edge with a force of 20 N perpendicular to the door, what is the moment about the hinges
Moment = 20 N × 0.8 m = 16 Nm
A crowbar is used to lift a rock. The effort force is 250 N applied 1.2 m from the pivot. Calculate the moment
Moment = 250 N × 1.2 m = 300 Nm
A see-saw is balanced. Sarah (weight 350 N) sits 2 m from the pivot. David sits 2.5 m from the pivot on the other side. What is David's weight?
Moment Sarah = Moment David. (350 N × 2 m) = (Weight_David × 2.5 m); Weight_David = 700 Nm / 2.5 m = 280 N
A force of 15 N is applied to a spanner at a distance of 20 cm. Calculate the moment in Nm
Moment = 15 N × 0.2 m = 3 Nm
