Questions tagged [friction]

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13
votes
1answer
375 views

Additional jacking force to overcome stiction/dry friction

It is common to lift bridges to replace bearings, etc. In an ideal world the lifting capacity required of the jacks would be the self-weight of the bridge divided by the number of jacks (+ allowances ...
9
votes
2answers
2k views

What causes friction in magnetic bearings?

Magnetic bearings work by levitating a rotating shaft so that it is not in contact with its supports. This greatly reduces the friction of the system. In all of the literature that I have seen on ...
9
votes
0answers
235 views

What type of ultrasonic transducer would be suitable for ultrasonic welding? [closed]

Project background: I am working on a project where i need to weld plastic using ultrasonic transducers. Problem: Since I'm still learning engineering, I have a hard time figuring out what all the ...
8
votes
5answers
7k views

How do you attach something temporary to a smooth metal shaft?

I want to attach something small to the smooth metal shaft of a small motor (2-3 mm in diameter), like fan blades, but I want it to be temporary. If I make it too loose, then the fan won't turn at ...
8
votes
2answers
5k views

Not a good idea to rub two of the same material against each other?

I've read that it's not a good idea to rub two surfaces of the same material against each other, e.g., plastic against plastic, metal against metal. Plastic against metal is preferred. Why is this the ...
7
votes
5answers
7k views

How can I improve traction on a wheeled vehicle yet reduce friction?

This is inspired by a project I undertook for my Physics class last year; I'd like to apply it in the future. Background: For the project, I and a few classmates were required to build a small car ...
7
votes
2answers
456 views

Wheelbarrow minimize wear

I have a question about the design principle. To explain my problem I made the sketch "wheelbarrow". To minimize wear, which design is preferred?
7
votes
2answers
121 views

Adding a lubricant to an already lubricious material, how is CoF affected?

I have a dry film moly-graphite lubricant (CoF=.075) and a lubricious CVD coating (CoF=.05). The CoF of each of these lubricious materials was determined using the same ASME standardized test. The ...
6
votes
2answers
1k views

Are jeweled bearings commonly used for applications other than mechanical timepieces?

Jeweled bearings use a metal spindle with a jewel lined pivot hole (pictured below). They have been important in the manufacture of mechanical timepieces since the early 1700's. Their importance ...
5
votes
3answers
913 views

Why is the friction factor in laminar flow independent of pipe roughness?

The Darcy friction factor is defined as: $$f_D =\frac{64}{Re}$$ with $Re$ I mean Reynolds number (global). I was wondering why Darcy in laminaire flow is independent of pipe roughness (wall roughness)?...
5
votes
1answer
75 views

Quantifying and measuring friction under extreme conditions

I want to quantify friction between a bullet and barrel to test different friction-proofing coatings and treatments. Is there a controlled test I could do at low speeds in a lab between samples of ...
5
votes
1answer
304 views

Deriving the amplitude of a coulomb (dry friction) damped spring

This is my first time posting anything, but I could not figure out the derivation of the amplitude of the spring for the 4 first oscillations. I am not acquainted with the effect and calculations of ...
4
votes
1answer
92 views

Dimension of the unidirectional mechanical clutch

This is a problem from the book Engineering Mechanics Statics vol-1 by Meriam Kraige. The elements of a unidirectional mechanical clutch are shown in the figure.A torque $M$ applied to the outer ring ...
4
votes
0answers
125 views

Calculating a pull force between two pieces of plastic

I have an HDPE pin, 2 mm high, 2 mm diameter, that I impress into a flat plaque of hot HDPE. It is not hot enough to melt the pin, but still hot enough that the material will shrink 4% in 24 hours. ...
3
votes
4answers
21k views

Why use bushings of different material than what they contact?

I've heard that materials that need to slide against each other should be of different materials. Why is that?
3
votes
2answers
680 views

Suggestions for low friction surface materials for a “beltless static treadmill”

I'm currently developing a treadmill for clinic gait research. If I were to build a flat treadmill with no moving surfaces what materials or coatings would be worth exploring as walking surface. ...
3
votes
1answer
170 views

Ideal funnel design for powders

I'm designing a funnel/bottle for a powder. My goal is to have all of the bottle's powder contents come out when inverted. However, the powder has a tendency to stick to itself (like flour or brown ...
3
votes
1answer
479 views

Normal force between two boards

This is a problem from the book Engineering Mechanics Statics vol-1 by Meriam Kraige The rectangular steel yoke is used to prevent slippage between the two boards under tensile loads $P$ .If the ...
3
votes
3answers
912 views

Is a gear usually held to a shaft by friction or an adhesive?

So, where I work, we have this arcade game, which is a classic claw machine. IN order to raise the claw up and down the machine makes use of a worm gear, like so: (although for the meticulously ...
3
votes
1answer
136 views

Recreating Focaults Pendulum

I am having issues building a recreation of Focaults Pendulum (basic, inexpensive, undergrad project). At this point, I am going to purchase aircraft cable or suspension cable unless someone can ...
3
votes
1answer
2k views

Practical uses of superfluids [closed]

I am wondering whether and how superfluids (possibly at room-temperature, if that is possible at some point) can be of any practical use in mechanical or electrical engineering or other fields. I ...
3
votes
1answer
769 views

Determine coefficients of friction based on the torque required to rotate a part on a shaft

I'm trying to model a part that rotates on a shaft. I measured empirically that it has a static torque of around 500 N·mm and a dynamic torque of around 400 N·mm. I want to simulate it in CAD but my ...
2
votes
2answers
214 views

How to add friction to a rope without using abrasion

I have a pay-out winch. It is a spool of rope that has a disk brake attached to it, so I can control the torque required to rotate the spool. When the torque is very large, however, the rope begins ...
2
votes
3answers
188 views

Understanding net torque from an actuator

This will probably sound like a silly question, but here goes.... Let's say I have an actuator, with a torque rating of 1 Nm. I then connect it to a wheel, which starts rotating at a constant ...
2
votes
4answers
2k views

Is there any material that has a higher kinetic friction than static friction?

Is there a material that has higher kinetic friction than static friction? You can assume it's sliding on any surface you want. Better if you come up with one that has this property on a standard ...
2
votes
3answers
386 views

Why is the Bush of a motor not replaced with a ball bearing?

Ball bearing reduces friction to a large extent than sliding friction. Motors use a metal ring called bush which slides against the shaft when the shaft is rotating. If a force is exerted on the shaft ...
2
votes
1answer
87 views

Calculating Bending Force on a Fixed Metal Plate

At work we've had a steel pipe support break on us, and I can't for the life of me figure out what happened. Here's some background info: A long (125m) steel heating pipe (ø51mm) is suspended, resting ...
2
votes
1answer
27 views

Friction versus ratcheting pawl

We are working to design a lock mechanism and need to hold a square plunger out of a hole for extended periods of time (potentially years). The square plunger is under pressure from springs to return ...
2
votes
2answers
83 views

Acceleration of spool on conveyor belt

A spool has a mass of 500 kg and a giration radius of $k_G = 1.30m$. The spool lies on the surface of a conveyor belt, the static coefficient of friction is $\mu_S=0.5$. The spool is not moving at ...
2
votes
1answer
46 views

Why Does Particle Size Matter For Bridge Pillars here?

I was watching this engineering video here and it talks about a technique used to prevent the pillars of a bridge from falling over in an earthquake. The pillars of the bridge are partially submerged ...
2
votes
1answer
338 views

Calculate max deceleration without front wheel slipping (bicycle)

I am trying to calculate the maximum braking force/deceleration for a bicycle. Note: the question assumes only the front brake is used Free body diagram: For dry tarmac where I know there is enough ...
2
votes
2answers
49 views

How to keep lighting “barn doors” open

I have two alum plates (45cm x 20cm x 1mm) that are hinged on the long side with two 30 x 80 hinges (30 x 40 each tang) in the middle, and "L" bracket / 20mm brace at the ends secured with a M4 loc ...
2
votes
3answers
108 views

Building a machine from an ideal physics problem

I have a physics professor for whom I'd like to build a machine. Featured in a problem he is notorious for assigning students, originally from Kleppner and Kolenkow's "Mechanics," the machine causes ...
2
votes
1answer
531 views

Does oil actually “attract” dirt?

The conventional wisdom consistently holds that "oil (or grease) attracts dirt", giving rise to the need for seals and dry-lubricants. But I've always considered that to be loose thinking, the truth ...
2
votes
1answer
362 views

Material with strongest grip on Aluminium 6061

Attached is an example picture of a clamp that will be attached to a pipe made of Aluminium 6061-T4. The clamp should have very tight grip on the pipe and prevent it from slipping or rotating but the ...
2
votes
2answers
447 views

Materials to use for a low friction cable-pull

I'm posting this question on this stack-exchange site, because it appeared to be the one made for this kind of questions. If this happens to not be the case, I'm sorry, I didn't know better. Also ...
2
votes
2answers
2k views

Good material for friction disk for a torque hinge?

What kind of material(s) would make a good friction disk, or disks, for a friction hinge, or torque hinge? This will be for the hinge on an arm that needs to be adjustable and also hold it's position ...
2
votes
0answers
374 views

how to calculate required torque and rpm to through a 160 gram cricket ball horizontally at 160km/h velocity?

I am going to design a bowling machine. In this design, I'm going to use two motors that are being placed vertically and their shaft are attached with two horizontal identical wheels with a space of ...
2
votes
2answers
601 views

How Can You Calculate Force to Overcome Friction From an O-Ring Seal?

I essentially have a piston in a tube that is sealed with an O-Ring and actuated with a solenoid. The friction of the O-Ring however, is higher than estimated (guessed as far as I can tell) by the ...
2
votes
0answers
93 views

Torque needed to keep a wheel spinning at high RPM

I have a treaded wheel which is 16'' diameter and 4'' across (trailer wheel). If I want it to spin constantly at 2750 RPM, what amount of torque do I need to apply to combat friction and air ...
2
votes
0answers
57 views

how to calculate the speed ratio (Rotational speed to advancing speed) in friction stir welding

I am a student and I work in the friction stir welding of a hardened aluminium alloy 7075-T6, and I want to confirm about this information before I put it in the article. I found in the literature ...
1
vote
2answers
365 views

Does a washer really increase static friction force?

Suppose I have a bolt that goes through a hole in a plate and is under tension. If I place a washer between the bolt head and the plate, does static frictional force (torque actually) really double? I'...
1
vote
2answers
196 views

Disc Brakes - Swept Area , why is larger better?

I am trying to understand why a bigger swept area on disc brakes provides higher braking force for the same force being exerted on the brake lever/pedal by the rider. If we use the same exact brake ...
1
vote
2answers
170 views

What is the exact concept of bearings?

Mechanics books always highlight that the main advantage of bearings is to reduce friction, especially when we talk about them in rotational motion applications. The example of ball bearings is always ...
1
vote
3answers
1k views

Applications with combination of high friction and low wear?

What would be some common applications involving high friction and low wear rates? for example, gear-driven mechanisms which require high friction between the gear teeth but ideally low wear between ...
1
vote
2answers
67 views

Which design to maximize friction for a device standing on concrete?

I have a device 4cm X 5cm X 15cm that stands on asphalt/concrete/road. So, the device is taller than its base which makes contact with the asphalt. I want to maximize the friction so that the device ...
1
vote
1answer
30 views

Inertia and friction between gears

I have a question regarding inertia and friction between gears. I have a gear which is connected to the rod at one end and an electric motor which is connected to the other end. I know the torque of ...
1
vote
1answer
108 views

Hydraulic Brakes - Why motorcycle brakes more powerful than bicycle brakes?

I was wondering why motorcycle brakes have so much more stopping power than bicycle hydraulic brakes (Than can be found on mountain bikes for example). The rotor has a bigger size which gives better ...
1
vote
2answers
409 views

Mechanical device that creates friction when rotating?

I am designing a mock-up aircraft throttle, like one of these: In an airplane, it it slides forward and backward to control the thrust of the engines. The problem is, I am not sure how to go about ...
1
vote
1answer
249 views

Apply constant load to an electric motor - low tech way

I want to know how much I can over-drive a small electric motor. Its speed at the rated voltage is too slow, so I want to find a higher voltage that won't blow it. It will only be used intermittently, ...