Forces and Moments
Forces are vector quantities that cause translational motion, while moments (torques) cause rotational motion. A moment is the product of a force and the perpendicular distance from a point to the line of action of the force. The principle of moments states that for a body in equilibrium, the sum of clockwise moments equals the sum of counterclockwise moments.
Knowledge Check
1.A force of 50 N is applied perpendicular to a wrench at a distance of 0.3 m from the bolt. What is the moment about the bolt?
2.Two forces of 20 N and 30 N act in opposite directions on a seesaw. If the 20 N force is at 2 m from the pivot and the 30 N force is at 1.5 m, which direction does the seesaw rotate?
3.What is the resultant moment about point A if a 100 N force is applied vertically downward at a horizontal distance of 0.5 m from A?
4.A force of 200 N is applied at an angle of 30° to a horizontal bar of length 2 m. What is the moment about the fixed end?
5.A couple consists of two parallel forces of 60 N separated by 0.4 m. What is the magnitude of the couple moment?
6.If a force of 80 N is applied at the end of a 1.2 m lever arm at an angle of 45°, what is the moment?
7.What is the condition for a body to be in rotational equilibrium?
8.A 500 N weight is placed 1.5 m from the left support of a 3 m long simply supported beam. What is the reaction moment at the left support?
9.A force F is applied at point (x,y) with coordinates (3,4) from the origin. What is the moment about the origin if F = (10i + 5j) N?
10.What is the perpendicular distance from point A to a 150 N force if it produces a 45 N·m moment?