# how to work out the reaction force on a uniform rod??

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#1
so i know that the sum of the anticlockwise = sum of the clockwise moments, but how to work out the reaction force for a uniform beam with two reaction forces?

in this case we have two unknowns and im not sure how to go about it :/
0
2 years ago
#2
(Original post by Mimi9335)
so i know that the sum of the anticlockwise = sum of the clockwise moments, but how to work out the reaction force for a uniform beam with two reaction forces?

in this case we have two unknowns and im not sure how to go about it :/
Another rule is that all upward forces must equal all downward forces, this gives you two simultaneous equations.
1
2 years ago
#3
(Original post by Mimi9335)
so i know that the sum of the anticlockwise = sum of the clockwise moments, but how to work out the reaction force for a uniform beam with two reaction forces?

in this case we have two unknowns and im not sure how to go about it :/
1
#4
(Original post by Notnek)
so the question is this:

AB is a uniform rod of length 5m and weight 20N,. In these diagrams, AB is resting in a horizontal position on supports C and D. Find the magnitude of the reaction at C and D.

distance from A to C (C is a support): 1.5m
distance from C to D (another support): 2.7m
distance from D (the support), to B (the end of the rod): 0.8m
0
2 years ago
#5
(Original post by Mimi9335)
so the question is this:

AB is a uniform rod of length 5m and weight 20N,. In these diagrams, AB is resting in a horizontal position on supports C and D. Find the magnitude of the reaction at C and D.

distance from A to C (C is a support): 1.5m
distance from C to D (another support): 2.7m
distance from D (the support), to B (the end of the rod): 0.8m
Got it?
0
#6
(Original post by TastyChicken)
Got it?
im still trying to figure out how to apply the idea you mentioned, how would i get to the simultaneous equations bit without finding the moments first?
lol sorry for this hassle but its really bugging me
0
2 years ago
#7
(Original post by Mimi9335)
im still trying to figure out how to apply the idea you mentioned, how would i get to the simultaneous equations bit without finding the moments first?
lol sorry for this hassle but its really bugging me
No worries. Have you drawn out the problem, this often helps visualize what is happening?
Use the two rules to come up with two equations that contain the reaction force for C and D. Then you can apply simultaneous equations to solve it.
First set A as a pivot and calculate the equilibrium of moments, namely clockwise moments must equal anti-clockwise moments. Then use of the rule that all upward forces namely C and D must equal all downward forces ie. 20.
0
2 years ago
#8
(Original post by Mimi9335)
so the question is this:

AB is a uniform rod of length 5m and weight 20N,. In these diagrams, AB is resting in a horizontal position on supports C and D. Find the magnitude of the reaction at C and D.

distance from A to C (C is a support): 1.5m
distance from C to D (another support): 2.7m
distance from D (the support), to B (the end of the rod): 0.8m
There are two reaction forces, not just one, for the two points of contact. If we label these reaction forces as R (at C) and S at (at D) then we have moments to consider. If you take moments about point C, then you will end up with one equation and a single variable because R can be completely ignored. Hence you find S. Secondly, you can consider the fact that the reaction forces must sum to the weight force which means that R+S=20
1
#9
(Original post by RDKGames)
There are two reaction forces, not just one, for the two points of contact. If we label these reaction forces as R (at C) and S at (at D) then we have moments to consider. If you take moments about point C, then you will end up with one equation and a single variable because R can be completely ignored. Hence you find S. Secondly, you can consider the fact that the reaction forces must sum to the weight force which means that R+S=20
yes that makes so much sense! i managed to get the right answer (finally lol)

(Original post by TastyChicken)
No worries. Have you drawn out the problem, this often helps visualize what is happening?
Use the two rules to come up with two equations that contain the reaction force for C and D. Then you can apply simultaneous equations to solve it.
First set A as a pivot and calculate the equilibrium of moments, namely clockwise moments must equal anti-clockwise moments. Then use of the rule that all upward forces namely C and D must equal all downward forces ie. 20.
i drew a diagram and that helped massively to see what was going on, and ive solved it

thank you so much for your help, guys honestly I really appreciate it! May you have all the full marks in the world
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