Constraint forces do no virtual work: does this always apply?
Answers
Answered by
0
The thread title is my main question, but to give some context, I'll include a particular example that made me ask the question in the first place.
In Hand and Finch, a small block is on a frictionless inclined plane on a frictionless surface. F1F1 is the constraint force on the block that holds it perpendicular to the inclined plane surface, F2F2 is the force on the inclined plane that counteracts gravity (the force by the floor on which the plane sits), and FgBFgB and FgPFgP are the gravitational forces acting on the block and the plane respectively. The inclined plane can slide along the horizontal surface.
The book states that constraint forces F1F1 and F2F2can do no virtual work because they act perpendicular to the directions of motion, and gravity is the only force which can do virtual work in this problem. Thus
δWIP=0δWSB=mgsinαδdδWIP=0δWSB=mgsinαδd
but the inclined plane moves horizontally, and that is because by Newton's third law, −F1−F1 acts on the plane. So even though F1F1 is a constraint force, it seems to have a component parallel to the direction of motion of the inclined plane. So shouldn't there be virtual work done on the inclined plane?
In Hand and Finch, a small block is on a frictionless inclined plane on a frictionless surface. F1F1 is the constraint force on the block that holds it perpendicular to the inclined plane surface, F2F2 is the force on the inclined plane that counteracts gravity (the force by the floor on which the plane sits), and FgBFgB and FgPFgP are the gravitational forces acting on the block and the plane respectively. The inclined plane can slide along the horizontal surface.
The book states that constraint forces F1F1 and F2F2can do no virtual work because they act perpendicular to the directions of motion, and gravity is the only force which can do virtual work in this problem. Thus
δWIP=0δWSB=mgsinαδdδWIP=0δWSB=mgsinαδd
but the inclined plane moves horizontally, and that is because by Newton's third law, −F1−F1 acts on the plane. So even though F1F1 is a constraint force, it seems to have a component parallel to the direction of motion of the inclined plane. So shouldn't there be virtual work done on the inclined plane?
Answered by
2
The thread title is my main question, but to give some context, I'll include a particular example that made me ask the question in the first place.
In Hand and Finch, a small block is on a frictionless inclined plane on a frictionless surface. F1F1 is the constraint force on the block that holds it perpendicular to the inclined plane surface, F2F2 is the force on the inclined plane that counteracts gravity (the force by the floor on which the plane sits), and FgBFgB and FgPFgP are the gravitational forces acting on the block and the plane respectively. The inclined plane can slide along the horizontal surface.
The book states that constraint forces F1F1 and F2F2 can do no virtual work because they act perpendicular to the directions of motion, and gravity is the only force which can do virtual work in this problem. Thus
δWIP=0δWSB=mgsinαδd
δWIP=0δWSB=mgsinαδd
but the inclined plane moves horizontally, and that is because by Newton's third law, −F1−F1 acts on the plane. So even though F1F1 is a constraint force, it seems to have a component parallel to the direction of motion of the inclined plane. So shouldn't there be virtual work done on the inclined plane?
In Hand and Finch, a small block is on a frictionless inclined plane on a frictionless surface. F1F1 is the constraint force on the block that holds it perpendicular to the inclined plane surface, F2F2 is the force on the inclined plane that counteracts gravity (the force by the floor on which the plane sits), and FgBFgB and FgPFgP are the gravitational forces acting on the block and the plane respectively. The inclined plane can slide along the horizontal surface.
The book states that constraint forces F1F1 and F2F2 can do no virtual work because they act perpendicular to the directions of motion, and gravity is the only force which can do virtual work in this problem. Thus
δWIP=0δWSB=mgsinαδd
δWIP=0δWSB=mgsinαδd
but the inclined plane moves horizontally, and that is because by Newton's third law, −F1−F1 acts on the plane. So even though F1F1 is a constraint force, it seems to have a component parallel to the direction of motion of the inclined plane. So shouldn't there be virtual work done on the inclined plane?
Similar questions