Mechanical Engineering: Ch 11: Friction (30 of 47) Wedge (Splitting Wood) Example

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In this video I will find the resultant force of the when a W=720lb is applied to a wedge splitting wood.
Next video in this series can be seen at:
• Mechanical Engineering...

[@Ducky_shades]

The videos are great and I love them. I am sure I am not the only one, but I notice in your videos there is usually a free-body diagram ready, this is problematic if you come across a problem in which you need to interpret a question. Suggestion: do some videos with a plain problem and break it down from a diagram, it becomes more beautiful.

[@MichelvanBiezen]

Thanks for the tip! We do both as it speeds up the video a bit.

[@GeorgePatterson-Waite]

for this example, how could you work out the force applied from the wedge on the log if you only knew how much (length) the wedge had been pushed in? imagine there was a wedge cut out in the log which the wedge fit into and then you started to move it down through the log by a known distance? how would you calculate the force applied to the edges of the log (against the wedges) as the wedge moves down in known increments? (assuming the tapered hole in the log has no bottom and is a straight through hole)

[@MichelvanBiezen]

If the distance is not known then you cannot solve the problem.

[@Mr71paul71]

so what ever force you put into the wedge is increased by 2.4 times in the force generated to split the wood. wedges are pretty interesting tools

[@renatoberaldo2335]

i wonder how one person can have this amount of science knolowedge in mind .. amazing.... and why dont you fix your calculator on the board ?

[@smallbeno1824]

Why was the 12 degrees divided then added to 16.7

[@MichelvanBiezen]

6 degrees + 16.7 degrees = 22.7 degrees. The angle at which the forces act must take into account the friction force.

[@arinzeanthony7447]

Does it also mean we should find the frictional force between that wedge and the ground? Cause I did and got nearly the same answer.

[@MichelvanBiezen]

Not sure what you mean by "between the wedge and the ground".

[@arinzeanthony7447]

@@MichelvanBiezen for example, if the wedge is divided, it goes right and as a result the frictional force between the wedge and the floor moves to the left. I tried it that way and got almost the same answer as yours. That's why I was asking whether my approach was correct because I don't understand this method, I use the "resolution of force method" to solve mine, so I was trying to figure a way of solving that with my method.

[@coryshannon449]

A question about some numbers. So the output force is 2.3907 times the input on both sides, but the mechanical advantage is 9.4093 times the input. When do we consider the mechanical advantage of a wedge rather than its reaction force? And I have a follow up question if that's alright.

[@MichelvanBiezen]

The machanical advantage is usually expressed in terms of the ration of the force generated divided by the force applied.

[@coryshannon449]

@@MichelvanBiezenthank you for responding! I thought that a wedges mechanical advantage was its length divided by width. Or 2 divided by the tangent of the angle. My follow up question is how do I apply the reaction force to cutting a given material with known shear and tensile strength? How does the pressure on the edge effect the cutting process if I reduce its sharpness or bluntness?

[@MichelvanBiezen]

Because the cos of a small angle is nearly one, the ration of the length over the width of the blade approximates the force exerted by the sides / force applied to the wedge.

[@coryshannon449]

@@MichelvanBiezen so how do I use this knowledge and apply it to cutting vegetables meats and woody things?

[@jakeyoung3117]

Why are the reaction forces not perpendicular to the wedge?

[@MichelvanBiezen]

The reaction force is a vector sum of the normal force and the friction force.

[@jakeyoung3117]

That makes sense, thank you!

[@HumbledGoat]

I hope you read this in time as I have a deadline tomorrow, but which formula do I have to use to calculate how much force you need to clove a piece of wood? Which material property do you have to look for in the stress-strain curve? I want to know how much force you need to split a 2000mm long chestnut pole with a diameter of 80mm into 4 pieces with a hydraulic cylinder. Thanks for the video by the way :)

[@MichelvanBiezen]

Without context, it is difficult to determine which equation (or method) to use. My guess is that if they didn't give you the dimensions of the wedge blade (and angle), that they expect you to use the shear stress/strain equation. You will need to find the shear strength of the wood in question.

[@HumbledGoat]

​@@MichelvanBiezen Hey thanks Michel for the quick response, I think that will do for now. It is for my internship (as a product designer), the person who made the machine doesn't have a 'list of requirements'. So I'm making one for him. I do have all the dimensions as I also drew the machine in Solidworks. One of the logical requirements is that the machine is capable of splitting a 2000mm chestnut pole. I wanted to specify the requirement by clarifying the minimum force needed to split it. I'm glad you mentioned the wedge blade because this also affects it. I'm not a mechanical engineer with hard physics, more a designer, yet I do like to figure out the technical aspects, as this will also show willingness to become a solid all-rounder. By the way you have a Dutch surname, are your parents from Holland?

[@MichelvanBiezen]

You may want to look up some specifications on these types of machines on the internet. You'll get a better understanding that way without tackling the physics equations. I grew up in Belgium (the name is Flemish).

[@HumbledGoat]

@@MichelvanBiezen Okay dankjewel voor de tip ;)

[@MichelvanBiezen]

Met plezier.

[@manikkumar8171]

Thank you so much

[@yh7184]

why is this exclusive to mechanical engineering? Btw you're great sir!

[@MichelvanBiezen]

There is indeed a lot of overlap between the sciences and engineering. However that said, the techniques used in mechanical engineering are often different than the techniques used in physics.

[@michaelduke9086]

Voice is different. What happened?

[@MichelvanBiezen]

We do get sick at times, but the videos must go on.......

[@michaelduke9086]

Physics - Mechanics: Torsion (3 of 14) What is the "Second Moment of Area"? How do I access 4, 5....14? Please don't get sick. TKS

[@MichelvanBiezen]

We are still working on those. They will be published soon.

[@creatosoloperte]

thanks!

[@MichelvanBiezen]

Welcome!