- #1
chetzread
- 801
- 1
There's also 215kN force acting to the right of section BC, right?David Lewis said:
How about the 215kN force? It's also acting on section BC, right?Simon Bridge said:
If ignore the force on the right, we should also ignore the forces on the right?David Lewis said:
if i make an imaginary cut, the forces on the left and right of the rod are ignored, then i only have 325kN , how could that be?David Lewis said:
do you mean we only need to cut at C?i thought we must cut at B and C to get section BC ?David Lewis said:
deletedDavid Lewis said:
If so, not all the forces are included for sectionDavid Lewis said:
What David is explaining is that you must start out by specifying your free body, and then do a force balance on your free body, including only forces acting on the specified free body. In this case, David has specified as the free body the portion of the rod to the left of BC. So you cannot include the forces to the right of BC, since they are not acting on your free body.chetzread said:
ok , if i want to cut off section BC from the others , then the force act on the left end of the rod is 715-325= 390kN to the left ( point away from the rod) ?Chestermiller said:
The internal force acting on the free body to the left is pointing to the right. The internal force acting on the free body to the right is pointing to the left.chetzread said:
so , in my working above , it's external force , am i right ?Chestermiller said:
Huh?chetzread said:
the force act on the left end of the rod is 715-325= 390kN to the left ( point away from the rod) ?Chestermiller said:
Yes.chetzread said:
Internal forces refer to forces that act within a system or object. These forces do not change the position or motion of the object as a whole, but they do affect the internal structure and movement of the object.
External forces refer to forces that act on an object or system from outside sources. These forces can change the position or motion of the object as a whole, and can include things like gravity, friction, and applied forces.
Internal and external forces can interact in various ways depending on the object or system. For example, a car's engine (internal force) can propel the car forward, while friction (external force) from the road can slow it down. In some cases, internal and external forces can cancel each other out, resulting in no overall change in the object's motion.
A balanced force is one in which the total amount of force acting on an object is equal in all directions, resulting in no change in the object's motion. An unbalanced force, on the other hand, is when the forces acting on an object are not equal, resulting in a change in the object's motion.
Internal and external forces play a crucial role in determining the stability of structures. Internal forces, such as tension and compression, help support the structure and prevent it from collapsing. External forces, such as wind or earthquakes, can put stress on the structure and potentially cause it to fail. Engineers must carefully consider both internal and external forces when designing structures for stability.
