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Resolving Forces

Resolving Forces

You can add forces together to give a resultant force. Did you know that a single force can also be broken down into component forces at right angles to each other?

Resolving forces is the process of finding two or more forces that, when combined, will produce a force with the same magnitude and direction as the original.

Vectors can have two parts when directed at an angle to the customary coordinate axis. Each of these is directed along with one of the axes, either horizontally or vertically. The process of breaking down a force into its Cartesian coordinate components is a common task when solving statics problems.

If a force pulled a particle upwards and to the right, that single force could be resolved into two separate components. The one directed upwards (vertical components), and the other directed right (horizontal component). This process can be done with the help of trigonometric functions.

Let's assume that the force exerted on the particle is 60N and is at an angle of 40 degrees above the horizontal. We can model this in the figure below to help resolve our force into two significant components.

Forces, Resolving forces, StudySmarterResolving forces example

Answer:

With this example, we will have to make projections on our figure to complete the right-angled triangle. From this, we see which sides of the triangles we will find – the sides of the triangles equal to either the horizontal or the vertical components of the force.

Forces, Resolving forces, StudySmarterResolving forces projection

Let the horizontal component be

And the vertical component be

Solving for the horizontal component:

Solving for the vertical component:

Resolving concurrent forces in equilibrium

When forces are applied to a body so that their lines of action meet at a point, they are considered concurrent forces. The result of these forces on a body can also be found with the help of trigonometric functions.

Given that the particle below is in equilibrium find the value of A and B.

Forces, Resolving forces, StudySmarterResolving forces acting on a particle in equilibrium

Answer:

First, let's complete the two right-angled triangles opposite the angles (shown below).

Forces, Resolving forces, StudySmarterResolving forces acting on a particle in equilibrium

According to trigonometry, the triangle with the side 2AN is a hypotenuse, 2Asin45 ° N is the side opposite the angle, and 2Acos45 ° N is the side adjacent to the angle. In the second triangle, AN is the hypotenuse, Asin45 ° N is the side opposite the angle, and Acos45 ° N is the side adjacent to the angle.

All forces will be resolved into their horizontal and vertical components separately. Let's start by resolving all of the forces in the diagram vertically. All values of forces that are working upwards are treated as positive values, and those that are working downwards are treated as negative values, as they are vectors.

The sum of upward and downward forces in equilibrium is zero.

2Asin45 ° N - Asin45 ° N - 50N = 0

Asin 45 ° N-50N = 0

Asin 45 ° N = 50N

Now, we're going to resolve horizontally to find the value of B.

All values of forces that work to the right are considered positive, and those that work to the left are considered negative.

The sum of all forces to the left and right is equal to zero in equilibrium.

2Acos45 ° N + Acos45 ° N - B = 0

3Acos45 ° N = B

We will now substitute A into the equation.

Resolving forces in a truss

A truss is a plane that takes advantage of the inherent geometric stability of triangles to distribute weight in harmony and to handle changing compressions and tension. They are a support system for structures that consist of a web of triangles to distribute pressure and tension evenly. A roof is a very good example of a truss.

There are a couple of steps to finding forces in a truss. Let's look at an example:

To analyse the following truss, you would have to break it down.

Resolving forces, Truss, StudySmarterTruss

Answer:

Step 1 . Create a free-body diagram of the entire truss which should include all forces. Ignore the individual triangles and label all distances and known triangles.

Resolving forces, Truss, StudySmarterThe free-body diagram of a truss

Step 2 . We will pick the pivot with the most unknowns and sum all the moments around it. We will pick point A in this case, and the formula here will be . The three moments around pivot A are:

  • Reaction force at B causing counterclockwise moment.
  • 500 lb applied force, causing a clockwise moment.
  • 150 lb applied force causing a clockwise moment

Resolving forces, Truss, StudySmarterMoments around pivot A in a truss

Step 3 . Sum all forces in the x-direction and equate it to 0.

Resolving forces, Truss, StudySmarterResolving truss to find x component

Step 4 . Sum all forces in the y-direction and equate it to 0.

We already found , so we will substitute that into the equation.

Resolving forces, Truss, StudySmarterResolving truss to find y component

Step 5 . We will use the method of joints to solve for tension and compression for each member since we now know what the three reaction forces are. Now, create a free-body diagram for each joint and label each member of the two endpoints:

Resolving forces, Truss, StudySmarterFree-body diagram of a joint in a truss

Step 6. We will now use trigonometric functions to resolve diagonal vectors into x and y components.

Resolving forces, Truss, StudySmarterresolving forces in a joint in a truss

Step 7 . Sum all forces in the y-direction and equate it to 0.

Step 8. Sum all the forces in the x-direction and equate it to 0.

Step 9. You can now repeat steps 5 through to 8 for every joint.

Resolving Forces - Key takeaways

  • A single force can be broken down into component forces at right angles to each other.
  • Resolving forces is the process of finding two or more forces that, when combined, will produce a force with the same magnitude and direction as the original.
  • Trigonometric functions help resolve forces into component forms.
  • A truss is a plane that takes advantage of the inherent geometric stability of triangles. It distributes weight in harmony and handles changing compressions and tension.
  • To resolve a force, make projections on your diagram to form right-angled triangles and use trigonometric functions to find the unknown x and y components.

Frequently Asked Questions about Resolving Forces

Resolving forces is the process of finding two or more forces that, when combined, will produce a force with the same magnitude and direction as the original.

First make projections on your diagram to form right-angled triangles and use trigonometric functions to find the unknown x and y components.

Project your angle of incline from the origin of the unbalanced force acting on the particle. Now you can have your right-angled triangle in addition to a known angle to help resolve forces using trigonometry.

Two components

Final Resolving Forces Quiz

Question

When two forces are broken down into two forces, the two forces are called....

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Answer

Component force

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Question

What is resolving forces about?

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Answer

Resolving forces is the process of finding two or more forces that, when combined, will produce a force with the same magnitude and direction as the original. 

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Question

Vectors, when directed at an angle to the customary coordinate axis can be considered to have how many parts?


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Answer

Two parts

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Question

When a force is resolved, the force directed upwards is called___

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Answer

The vertical component

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Question

When a force is resolved, the force directed to the right is called___


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Answer

Horizontal component

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Question

What mathematical functions are used to resolve forces?

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Answer

Trigonometric functions

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Question

What are concurrent forces?

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Answer

If the forces applied to a body are such that their lines of action meet at a single point, they are called concurrent forces

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Question

What is a truss?

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Answer

A truss is a plane that takes advantage of the inherent geometric stability of triangles to distribute weight in harmony and to handle changing compressions and tension. 

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Question

What is a common example of a truss?

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Answer

A roof 

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Question

A force is being exerted on the particle is 12N and is at an angle of 68 degrees above the horizontal, what is the magnitude of the vertical component?


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Answer

11.1N

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Question

All values of forces that are working upwards are treated as:


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Answer

Positive values

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Question

All values of forces that are working downwards are treated as:


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Answer

Negative values

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Question

To analyse a truss, you must create a free-body diagram of the entire truss which should include all forces and ignore the individual triangles. Is this statement true or false?

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Answer

True

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Question

If a force was being exerted on a particle with the magnitude of 120N and is at an angle of 56 degrees above the horizontal, what will be the component forces if resolved?

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Answer

67.1N to the horizonal

99.5N to the vertical

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