First of all, you sayhow then can tensions forces in this photo be equal if their sources are of different weightThis shows a fundamental misunderstanding. The two weights are not the 'sources' of the tension. The tension results from the interaction between the whole rope and both masses.Somewhat expanding on the good answer from @Eeko, you might try the somewhat unusual approach of drawing the free body diagram for a small piece of the rope. Focus on a piece of the rope that isn't in contact with the pulley. What is this piece of rope touching? The only things it touches are the adjacent pieces of rope that it is attached to, and they can only exert tension forces on it (one tension up, the other down).
The only other force that could act on this piece of rope is gravity.Now, taking up as positive Newton's 2nd law reads:$ma = T1 - T2 - mg$,where $T1$ and $T2$ are the two tensions and $m$ here refers to the mass of this piece of rope. We usually approximate ropes as massless.
So this gives us$0 = T1 - T2$.So the tensions exerted above and below this piece of rope have to be equal. Since this has to be true for any part of the rope the tension must be the same throughout the rope.But look at why we got this result.
We had to assume that the rope was massless. (tension the same everywhere in the rope is often called the 'massless rope approximation) If you assume (more realistically.) that it isn't massless then $T1 neq T2$.
If the rope is heavy compared to the hanging masses then you can't get away with this approximation and the tension isn't the same everywhere in the rope. This makes the problem harder. Usually the massless rope approximation is a pretty good approximation and since it makes life so much easier we use it. $begingroup$ Just considering the rope segment, no pulley, tension 2 goes all the way from the left, where mass 2 is hanged. Tension 2 will be pointing down, along with the weight of that segment. And tension 1 is on the right, where mass 1 is hanged, and going up.
You said 'ma' is positive, so tension 1 is bigger than the sum of the other two forces, or bigger than tension 2. If tension results from interaction of two masses, and neither can produce it on its own, how then is tension 1 bigger than tension 2? $endgroup$–Aug 14 '15 at 21:27. Eso health bar addon. $begingroup$ No @user132522 you've misunderstood my argument. Think of this little piece of rope (on either side). The only things it is in contact with are the piece of rope just above it and the piece of rope just below it. Aside from the Earth exerting a gravitational force, the only things that can exert forces on it are the piece of rope just above it (which pulls up on it) and the piece of rope just below it (which pulls down on it).
Call these $T1$ and $T2$ and now reread my answer above. Also, I never said $ma$ is positive. In the approximation $ma=0$ for the piece of rope. $endgroup$–Aug 18 '15 at 3:13.
I think you're misunderstanding what it means when by 'the pulling force equals the tension force'. Imagine pulling on a rope with the other end not fixed to anything. Even if you pull with a large force, the tension in the rope will be zero, since the whole thing is accelerating due to that force. So what's important to understand from this is that tension is determined by pulling on both sides of the rope, not just either side individually.Another helpful method for understanding why the tension must be the same all the way through, is to think of it as an equilibrium problem. Imagine a rope where the tension varies along it's length, for simplicities sake we'll say it varies evenly from a large T on the left, to a smaller t on the right.
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If we look at a small piece of the rope, it will have a larger force pulling it to the left, and a smaller force pulling to the right. So that one piece gets pulled to the left, which decreases tension on the left side, and increases it on the right.Hopefully you can see from that example that having a rope with equal tension throughout is the only stable configuration.
There's no inconsistency because the system isn't in static equilibrium. The net force on the larger mass is $2mg-T$ and it will accelerate downwards. The net force on the smaller mass is $T-mg$ and it will accelerate upwards.
If the string is inextensible, the two accelerations have equal magnitude and you can solve for $T$.BTW, you shouldn't put plus or minus signs on a vector diagram: the arrow shows the direction and the accompanying number or letter shows the magnitude. A negative sign in particular is misleading (does the vector point in the negative coordinate direction or in the opposite sense to the arrow?). There are two points to note:Firstly, the tension T1 and T2 is equal only when the pulley and the rope are massless. If the pulley has mass= it will have considerable inertia momentum. Due to its angular acceleration, its torque will be different from 0, which implies that T1 and T2 is not equal.Also, if the rope is not massless, the tension will also be different.
Imagine each part of the rope then acts as a mass. Then the tension is not the same everywhere in the rope.Secondly, if all these conditions are satisfied, then T1 and T2 are equal. It is plausible as the two forces have two different functions,one acts as a retarding force, whereas the other is an accelerating force.
It is such that the system can run at the same acceleration.
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Tension, for me, is a tricky thing.After finishing a related chapter of my book and watching a video, I still can't get a hang of it.Here is a situation:My knowledge is that tension, just like normal force, happens in just the same way, but with the difference of a string attached.It is understandable that in the picture, the string attached to the hanging mass has a tension directed upward, because it's weight is directed downward. (Action and reaction)But what intrigues me is that applying the same logic, the horizontal mass is being pulled to the right, it would have been understandable if the tension is directed to the left.alsoCan I think of tension as the reaction force when you pull, and normal force when you push?updateIf I was to think tension as a reaction force in the first picture for the horizontal mass, then can the frictional force be the action force?(Ehh, I don't think that makes sentence. Friction is always reaction).
We treat the string/rope like another object. This object exerts forces on other objects such as the hanging mass (in your picture).
However, a string, by its very nature, can never 'push' another object, it can only 'pull' another object. That 'pull' is a force which we give the name tension.Thus, tension will point away from the mass in the direction of the string.
In the case of the hanging mass, the string pulls it up, so the string exerts an upward force on the mass, and the tension will be upwards. In the case of the mass on the table, the string pulls it to the right, so the tension will be to the right.So, for example, suppose you have a rope attached to a mass on a friction-less table, and you pull the rope to the right with a constant force of 1 Newton. The rope will then pull on the mass with a force of 1 Newton to the right, and the mass will start to accelerate to the right. Here, the tension, (i.e.
The force with which the rope pulls on the mass) is to the right with a magnitude of 1 Newton. So, you created tension by pulling on the rope; a tension of 1 Newton.I don't quite understand why you keep referring to the normal force.
A normal force is a force perpendicular to a plane of mass; the mass we refer to here we consider to be an ideal case of a point mass, so there is no normal force. Also, the rope can be pulled in any direction, not just the direction perpendicular to the plane of the mass.Tension is created whenever a rope exerts a force (pull) on another object. Notice that there was no friction in the example above.
You don't need friction to have tension; this experiment could have been done in space. Tension is an internal force in a body, such as a rope, that resists any attempt to pull the rope apart. Simply, tension arises due to intermolecular interactions, and if it did not exist, ropes would fall apart the moment you pull on them.Now, it is necessary to distinguish between internal and external forces for a body. External forces are forces that act on the body due to other bodies, such as friction and gravity.
When you look at the body as a whole, it is easy to see the effect of the force on the body. External forces allow the bulk of the body to accelerate, provided no other external forces cancel them out (equilibrium). For example: a body acted upon by the Earth's gravity:Internal forces of a body are different. Internal forces exist inside a body, and the effects of internal forces cannot directly interact with anything external to the body. In other words, internal forces are forces that one part of a body causes onto another part of the same body (see later). Hence it is not as clear to see the 'direction' of such forces. Internal forces do not lead to bulk acceleration, but instead cause body deformation (e.g.
Stretching a spring, or bending a ruler). Here is a diagram showing the internal forces acting on a block:Well, you can't see anything obvious on the outside, but that not because internal force don't exist. It's because if you were to take all of the internal forces present in a body, they would sum to zero. This is a result of Newton's 3rd Law.
Instead, a better way to visualise internal forces in a body is to make an imaginary cut through the body and see how the forces act on the cut face. This is better demonstrated below in the diagram, where a rope is being pulled apart:By considering an imaginary cut, you look at the two halves and enforce equilibrium (if the whole rope obeys equilibrium, so must any arbitrary sub-length of rope).
By doing so, you find out that in order to satisfy equilibrium, one half must exert a force on the other, and vice versa by Newton's 3rd Law. These particular forces are internal since they're forces caused by one part of the rope acting on another part of the same rope. These internal forces act at the interfaces of the imaginary cut, and, in this case, are known as the tension.
To be more precise, it is the tension at the location on the rope where the imaginary cut is made. Note that you can determine the tension's direction if you look at one half of the rope, but since the tensions occur in pair, there is no obvious direction of tension at that point of the rope for the whole rope.Looking at your example, let's make a few cuts to see the tension forces in the rope:Only the forces acting on/in the rope, on the box or on the hanging mass are included in the diagram above.In short, internal forces like tension at a particular point in a rope doesn't really have a clear cut direction, as they occur in pairs. The tension on a string between two objects (note: your top diagram shows t̲h̲r̲e̲e̲ objects) is analogous to the force between two objects elastically colliding.
The force exerted by the one end of the string is opposite and equal to the force exerted by the other end of the string; both forces must be parallel to the string and pointed towards its center.However, do not confuse the string tension with a force. Even though it will have the same magnitude as the force on either end of the string, and is oriented along the length of the string, tension does NOT have a direction. You can't say 'The tension is headed to the left' and be making any sense.
Learn how to use the tension devices on your sewing machine and how to thread for proper tension.Don’t stress over finding the correct thread tension on your sewing machine. Here’s what you need to know about setting and adjusting thread tension dials.Many sewers avoid the dials on their sewing machines like the plague, certain they’ll only make matters worse if they make adjustments.
In fact, there’s nothing mysterious about setting and adjusting thread tensions on your, whatever its make and model. What’s potentially more confusing is that many apparently tension-related problems are caused by factors other than misadjusted tension dials.Let’s look closely at how to identify and correct “tension” problems, with and without touching the tension settings. Tension devices and proper threadingYou can’t get proper tension without correct threading.All machines have basically the four tension devices shown: thread guides, tension discs, tension regulator for upper thread, and bobbin-case spring for bobbin thread. These ensure that the same amount of thread flows simultaneously from the needle and the bobbin, producing a symmetrical stitch. Meet your tension toolsIn order to form a row of stitches that looks the same on both sides of the fabric, the same amount of thread needs to flow from the spool and the simultaneously. This is accomplished by running the threads through various tension devices, including the thread guides, tension discs, and tension regulator on the machine head for the upper thread(s), and the bobbin-case spring for the bobbin thread. Some machines include a small hole in the bobbin-case finger, through which to feed the bobbin thread to increase the tension for improved stitch definition when, and, without touching your tension settings.The tension discs and tension regulator together are called the tension assembly.
The tension discs squeeze the thread as it passes between them, while the tension regulator controls the amount of pressure on the discs. On older machines, there are only two tension discs, controlled by a screw or knob. On newer models there are three discs controlled by a dial or key pad on the front of the machine, which can regulate two threads at once.In either case, the tension regulator is elementary: When adjusted to a higher number (turned clockwise), the discs move closer together, increasing the amount of pressure. Turned to a lower number (counterclockwise), the discs move apart, decreasing the pressure.
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Using a thicker thread without resetting the dial will increase the pressure and cause the upper thread flow to decrease, unless you’ve got a newer machine that makes automatic upper-tension adjustments. Since the bobbin tension is not self-adjusting, the lower tension may need to be adjusted manually to match.In addition to guiding the thread along its path, each thread guide exerts a small amount of resistance on the thread, adding to the tension from the discs to achieve balanced tension. Bottom line: Always make sure all guides are threaded before stitching.The flat bobbin-case spring exerts pressure on the thread as it comes out of the bobbin case. The amount of pressure is regulated by a small screw at the rear of the spring. Both the spring and screw are easy to locate when the machine has a separate bobbin case.
When the machine has a drop-in bobbin with a built-in bobbin case, locating the tension screw can be more challenging. Both types are shown in the drawings below. In either case, to increase the resistance, use a small screwdriver to turn the screw clockwise (to a higher number) or counterclockwise (to a lower number). Turn the screw in small increments and never more than a quarter-turn between tests.
This helps you keep track of how much you’re changing your settings and reduces the risk of losing this tiny screw. The bobbin-spring screw regulates bobbin-thread tension, whether your bobbin is a separate, drop-in unit (left) or is built into the machine (right).As with the tension dials, the amount of pressure will be increased when thicker threads are run under the bobbin spring. To eliminate the need to fiddle with the bobbin-case screw, many sewers (myself included) have two bobbin cases: one set for general sewing and the other for adjusting to less frequently used threads. Recognizing balanced tensionsWhen the tensions are balanced, the stitched line looks good on both sides of the fabric, as shown at the top of the illustration below, and the seam is at its strongest and most elastic.
The easiest way to spot unbalanced tension is to look for visible knots or loops at the end of each stitch. When the bobbin thread shows on the right side, the needle tension is too tight or the bobbin thread, too loose, as shown at left in the illustration below. When the needle thread shows on the wrong side, the needle tension is too loose or the bobbin thread, too tight, as shown at right in the illustration below. Of course, if you’re sewing on thin or lightweight fabrics, both threads may show on both sides when the tension is balanced, simply because the fabric is so thin. When upper and lower thread tensions are balanced, knot between top and bottom threads is hidden between fabric layers (top). When lower tension is too loose (or upper tension is too tight), knot is visible on right side (left).
When upper tension is too loose (or lower tension is too tight), knot is visible on wrong side (right).Tensions can still need adjustment even if they’re balanced. If both tensions are too tight, the seam may pucker, or break easily when stretched (test this on the more stretchy crossgrain, with at least a 6-inch seam).
If both are too loose, the seam will gap when pressed open, exposing the threads between the sections.How to adjust tensionThere are two types of tension adjustments, a basic adjustment for everyday sewing (this is what your repair person does when adjusting tension, but you can do it, too) and a temporary adjustment, necessary when you change thread types or sizes, fabrics, and stitching operations.To make a basic adjustment, select contrasting colors of a thread in the brand, size, and fiber you use most frequently. Use one color to fill the bobbin, with the machine set on medium speed to reduce the risk of stretching the thread. Insert a new needle in the size you use most frequently and thread the machine, using all the thread guides on the machine head, but skip threading the eye on the bobbin-case finger if you have that feature.Set the stitch length for 2 mm (12 stitches per inch) or for the length you expect to use most frequently. Set the upper-tension regulator at the middle of its range (on most machines, this is 4 or 5), and stitch a test seam on two layers of lightweight muslin, then examine the stitches.
If necessary, use a magnifier to see the stitches clearly. If the tension isn’t perfect, fix it by adjusting the bobbin spring; tighter if the bobbin thread shows on the upper layer, and looser if the needle thread shows on the underlayer.
Make another test seam, and examine the stitches, repeating until the stitch is balanced.Once your stitching is balanced, start a tension log in your sewing-machine manual, indicating the thread brand, size, and type, as well as the number on the upper-tension regulator that produced a balanced stitch. Then draw a picture showing the position of the bobbin screw, like the example below, to use as a reference if you need to record a change in bobbin settings for special threads. To record the bobbin tension for future reference, make note of the bobbin-screw position, including reference to thread opening or open side of bobbin case.To make a temporary tension adjustment, select the threads for the needle and bobbin, then fill the bobbin and thread the machine. Make a test seam on the fabric that you plan to sew, examine the stitches, then see if you can find a balance using the upper-tension assembly alone.Whenever you switch from your standard sewing thread to another thread, first thread your sewing machine and test your setup to see if you can get away with a tension-dial-only, temporary adjustment. If that doesn’t work, get out your second bobbin case, and start moving the screw in quarter-turns to loosen or tighten it, as your sample dictates. Typically, when you use a lighter-than-normal thread for both needle and bobbin, the tensions will stay balanced, even though they’re both lighter.
This is often just what you need to avoid puckering lightweight fabrics, so no adjustment may be necessary. A heavier thread in top and bottom will increase both tensions, and you’ll probably need to set a lighter tension to accommodate heavier fabrics. Don’t touch that dialSo many things can affect the tension that it’s worthwhile to run through the following checklist in the order given before you reach for the tension regulator:. Incorrectly threaded machine: Incorrect threading is responsible for more “tension” problems than any other factor. Did you use all thread guides?
Did you thread with the presser foot down, thus keeping the thread from slipping fully between tension discs? Is thread unwinding freely from the spool, or catching on the spool’s slash? Are you using a bobbin as a spool (which can interfere with the thread flow)? Is the bobbin inserted correctly?. Incorrectly filled bobbin: Remove any thread on the bobbin be-fore you wind on new thread. Wind the bobbin following the machine instructions, so it’s evenly wound at the proper tension. Remove any thread from the outside of the bobbin.
Wind at a consistent, slow or medium speed, especially with polyester and nylon threads, to keep them from stretching; they relax in your seam, causing puckers. Dirty machine: Lint and thread ends lodged between the tension discs, under the throat plate, or around the bobbin case and bobbin, increase the resistance and restrict the thread flow. “Floss” between the tension discs with a lightweight, lint-free cloth, and check in the bobbin area for thread ends and lint. Damaged machine parts: Bent needles and bobbins, and rough or damaged surfaces on the needle eyes, thread guides, tension discs, take-up lever, throat plate, presser foot, bobbin case, and in the bobbin area can all cause problems. If you drop a metal bobbin on a hard floor, throw it away, even if it looks fine; the smallest damage can distort tension.
Avoid damage to the bobbin-tension spring by cutting the thread close to the case before removing the bobbin. Raise the presser foot before removing thread from the upper tension. Needles, threads, and fabrics: Different thread sizes and types on top and in the bobbin can throw off basic tension settings.
A needle that’s too large or small for the thread can also unbalance your stitches, because the size of the hole adds to or reduces the total top tension. June 25thI don't know if my problem is tension-related or not: when I start to sew, the stop motion knob spins free and when I lift the presser foot & remove the fabric, I find several threads @ 3 inches long looped on the bottom of the fabric instead of just a single bobbin thread. The troubleshooting list at the back of my sewing machine book does not address this problem. Could you at least identify the problem for me?
If possible, I would also appreciate an explanation of how to solve the problem. October 15thThis article is very well written and I want to thank you for it. I will print this and post it by my machine.I have a Baby Lock Quilter's Choice Professional on a New Joy Gold Standard frame. I have always experienced alot of thread breakage and I get so frustrated with it and will walk away from it for days.
I have 6 shirt quilts to quilt and Im not looking forward to it. I was experiencing my top thread showing on back, but I finally got that balances out. Now my bobbin thread is showing on top. I will work on balance that tonight.
Back to the thread breaking. I have tried different thread, different needles. I have threaded, unthreaded and rethreaded to no avail. I keep having the same issue. Im almost convinced now, it may be the way the thread is on the spindle. I noticed that when I have the presser foot up and I pull the thread thru, that it is smooth until more thread comes off the spool, then it almost jerk and releases smooth again. Any thoughts??
If you can help solve my ongoing problem, you will have a friend for life!! THANKS SO MUCH!!. October 28thFor the other Sue.It sounds like your machine's timing is off - I had that problem with one of my antique Singers, it didn't matter what I did, it broke thread or knotted severely.Not willing to throw my 1924 model 66 in the trash, or send it to Goodwill where I rescued it from, I looked around until I found a shop that would work on it.
It turns out. One of the lower arms bearings were loose, which made the bobbin case run just slightly out of time.Now, your babylock (I hope!!!) isn't as abused or old as this machine, but if you can't get the tension to tense right (after following the instructions on this page) it might be worth spending a few $$$ to have someone go thru it, and make sure it's timed right.If you're lucky, you'll find a repair guy who will let you watch what he does. Not likely your machine breaks again, but if it does, yo'll know what he did to fix it. IF you're handy with tools (and can find the repair book for the machine) you'll remember what he did, and better, keep your machine running like the techs!!!;). June 2ndI learned about using the right size needles for specific fabric, right type of thread for specific fabric such as polyester for polyester fabric & cotton for cotton fabric, not to use old or cheap thread not just color, even how to hold the fabric as it goes thru the machine matters but I could never get the tension right. I even learned about maintaining it regularly, using a new needle for every project but this is the first time I have learned this much about tension!
I don't understand what you mean about how to 'floss' between the tension discs. I'm not even sure where they are exactly and how to get to them. Can you give me for information on that please?. May 5thIn diet continue with the protein rich diet and foods like cereals, lentils, tofu, peas, fresh cheese, soya,sugar and rice. Here's an example of how the timing approach works.
So her diet would include 1219 calories (using example #1) or 1380 (using example #2) + an additional 40%. Spiropent is a brand name for the chemical Clenbuterol Hydrochloride or Clenbuterol HCL. Need not stick to 8 hours as you might not need that long to feel great.url=advertisements/url.
The problem statement, all variables and given/known dataAn ideal spring of unstretched length.20m is placed horizontally on a frictionless table as shown above. One end of the spring is fixed and the other end is attached to a block of mass M = 8.0kg. The 8.0kg block is also attached to a massless string that passes over a small frictionless pulley. A block of mass m = 4.0kg hangs from the other end of the spring.