# What is Brakes: Definition and 85 Discussions

A brake is a mechanical device that inhibits motion by absorbing energy from a moving system. It is used for slowing or stopping a moving vehicle, wheel, axle, or to prevent its motion, most often accomplished by means of friction.

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1. ### Thermal energy dissipated from the brakes in a car

My sign doesn't check out and I don't get why that'd be the case. Forces that act --> ##F_{fr} and F_g## derivation: ##\Delta K = W_{NC} + W_C (1)## ##\Delta K + \Delta U = W_{NC}## ##\frac 12 mv_2^2 - \frac 12 mv_1^2 + mgy_2 - mgy_1 = W_{NC}## NOTE: ##y_2## assumed to be datum line so ##y_2 ==...
2. ### Front brakes provide 70% of stopping power. But why?

I'm not disputing that front brakes on a vehicle provide the majority of stopping power, but why is that? I originally thought it was because of added traction at the front due to weight transfer, but even my bike moving at a walking pace has more powerful front brakes than the identical rear...
3. ### Eddy Current Brakes: where to with its current?

I've seen a documentary about the Yukon Route Railroad. Some trains are run by old steam engines (with Diesel). They also equipped their engines with eddy current brakes and said, that the resulting current is conducted into resistors and via thermal energy removed into air. I assume that...
4. D

### BLDC motor as generator to power eddy current brakes

Hi everyone - here's a concept that I'd like a few opinions on: As part of a project, I'm looking at using a brushless DC motor mounted on a high-speed vehicle as a generator. Once the vehicle hits its top speed, the batteries should disconnect from the motor and the vehicle's own velocity will...
5. ### Why does the car skid when brakes are applied too hard?

When the car is accelerating let's assume the force on it is ma. In order to stop this force we have to apply the brakes which apply a force in the opposite direction. But this force should not exceed ma. It is because the additional force will act on the tyres and create an additional...
6. ### Sizing hydraulic (brake) lines

On older GM cars, the brake lines are 3/16" from the front port of the master cylinder, splitting into two 3/16" for each front wheel, and 1/4" from the rear port of the master cylinder, splitting into two 3/16" for each rear wheel. This is the case for drum/drum or disc/drum configurations...
7. ### Eddy Current brakes operating at high speeds

Hi all, I'm currently working on eddy current brakes designed to stop a vehicle from speeds around 135 m/s. While researching eddy current brakes, I found the equations used to find the force generated tend to break down at higher speeds. The design is linear, stopping on an aluminum rail...
8. ### Work done on brakes vs kinetic energy lost by vehicle

When doing work on the brakes of a car or bicycle, how much of that energy is actually removed from the total kinetic energy of the vehicle? What is the most efficient braking system?
9. ### I Bike going downhill brakes front wheel

I'm an avid bike rider and a first year physics student. A couple days ago a friend of mine told me about how his friend was going downhill on her bike, used her front brake, and went over. I would like to determine what the minimum speed for a given slope angle is for the biker to do a full...
10. ### Calculating the force in suspension as a car hits the brakes

Hello, Firstly thank you for reading my post. This is an interesting question I was wondering if anyone here could teach me how to work out. Say if you had a large go-kart (FSAE/Formula Student if anyone knows of that) and you were driving at 120kph and hit the brakes and stopped in 3 seconds...
11. ### What is the meaning of 'uni directional control' for electromechanical brakes?

hello i have a system consisting of bi directional rotating shaft.i would like to integrate a brake in the system for stopping the shaft. i m interested in an electromechanical brake in thomas linear compnay's catalogue(http://www.thomsonlinear.com/en/product/SB-70B24-E32S). They have mentioned...
12. ### Using KE in elevator-system to design brakes?

Homework Statement Hello! I am doing some rough design on an elevator-system and I have now come to the brake. Here is my system: The text is norwegian but "rdriv" in the first image is "Rdrivskive" in the second image and it's this wheel that is dragging the rope. The "Brems" is where I...
13. ### Why would changing to a larger brake master cylinder decrease braking pressure?

Hi, I am in the process of restoring the brakes a 1974 Porsche 914 and upon reading up on a Porsche forum found a discussion about changing the original 17mm brake master cylinder with a 19mm one. A number of individuals indicated that doing so would reduce braking pressure and I was unclear as...
14. ### Is a heat vs Mu chart Misleading? What factors into Mu? (brake pads)

So I was trying to understand some Mu charts of Brake pads for cars. I thought that Mu was basically a "calculated, or measured constant " which could be used to compare friction between 2 materials. like a solid iron Rotor, and a brake pad. I was thinking that a simple chart that shows...
15. ### Automotive Do the brakes provide friction to tyres of bicycle/car?

Hello, members. I know that the cars and bicycles move on the road simply due to friction. How do the brakes of bicycle and car work to stop them? Do the brakes provide friction to tyres of bicycle/car to stop them from moving? I'm confused, could you please explain to me why do the brakes...
16. ### Calories generated in brakes of a machine

Homework Statement A 1000 kg mass car is driving at 3 [m/sec], how many kcal develop in the brakes till full stop Homework Equations Kinetic energy: E=\frac{1}{2}mv^2 Energetic equivalent of a kcal: 4186 [joule] The Attempt at a Solution ##E=\frac{1}{2}1000\cdot 9=4500[joule]##...
17. ### Calculate Car Deceleration and Stopping Distance | Cars Slam on Brakes

Homework Statement Car 1 travels 50km/hr Car 2 travels 100km/hr The Cars are 45m apart Car 1 slams on brakes and stops in 8m a) Calculate deceleration of Car 1? (Car 1 has the same deceleration as Car 2) b) Use deceleration to find the distance it took Car2 to stop? c) Did the...
18. ### Find the tension between two train carts as the train brakes.

This was from my last exam. I got this problem wrong. I feel like I should have known how to do it but I blanked out or something. Just coming here to figure out how it's supposed to be done. (This is from what I remember, numbers may be off from what was on the test) I know I got it wrong...
19. ### Band Brakes: Specifications, Durability, Safety & Performance

Can anyone elobrate what is the (specification, durability, safety, and performance ) for band brakes used in conveyor system...??Your help is much appreciated. Thank you.
20. ### Work, Force, and Brakes: Solving the Physics Problem

Homework Statement Use this information to answer the next 4 questions: The brakes of a 1452 kg car bring it to a stop from a speed of 17.2 m/s in a distance of 100 m. Homework Equations 15. How much work do the brakes do? 2.15 x 105 J 1.42 x 106 J 2.50 x 106 J...
21. ### Train brakes by lack of pressure?

Hi! An attempted explanation for the tragedy of Lac-Megantic is that the only running locomotive was shut down by the fire brigade when extinguishing it, and as this locomotive stopped to provide pressurized air to the train, the wagon's brakes opened and the train ran away. Which I can't...
22. ### When do the park brakes need to be applied=f(critical inclined angle)

The coefficient of static friction is defined at the critical/Maximum inclination angle at which the block "begins" to slide. Hence, for a vehicle on an inclined plane at this critical angle, the braking force at this critical angle is given by: i.e F_{braking}=\mu_{static} N at \theta _{max}...
23. ### Brakes on a car-Energy related question

In terms of energy, why does a car going fast absolutely needs good brakes? What are the main physical constraints to optimize? Friction should be increased. But, that's what I pretty much I have to say. What else could be said? I've been racking my brains for two hours picturing a car in my...
24. ### Do Disc Brakes Add Extra Weight to Cars?

what is the approximate weight of brake system used in cars? will disc brakes increase the weight?
25. ### Understanding the Viscosity of Glycerine and Oil in Hydraulic Brakes

Viscocity of glycerine is high than that of oil then why it can't be used in hydraulic brakes..?
26. ### Calculating Speed for Warmed Brakes on a Hill

Hello. I have got one interesting question for you. Imagine that you are driving a car down the hill. What is the speed to the most warmed brakes? Today I thought about it and I wonder how it somehow calculate numerically but I don't know how. Have you got any ideas?
27. ### Rotational Kinetic Energy of disc brakes

The disc brakes of a high performance car are often made of carbon fiber instead of iron, thereby reducing the mass. If both types of discs are of the same size and shape, and each iron disc has a mass of 4 kg and each carbon disc has a mass of 1 kg, what is the reduction in rotational kinetic...
28. ### Air brake over hydraulic brakes

Air brake over hydraulic brakes! Why air brakes are used in long vehicles like trains, instead of hydraulic brakes?
29. ### Why do trucks have bigger brakes?

I am a little confused about why a passenger truck like a Chevy 2500 or a Ford F250 requires brake rotors with larger diameters than a car like a Toyota. I have a degree in Physics, and although I have not used it in 10 years I specifically remember learning that mass does not effect braking...
30. ### Automotive Rear disc brakes on 88 monte carlo racecar problems

Have a 88 monte carlo racecar, reciently installed a 9in ford with disc brakes using metric calipers, can't use aftermarket master cylinders or proportonal valve, an have a problem with no rear braking, tried a corvette master cyclinder but didnt seem to help, any ideas??
31. ### If a 1000 kg car is moving at 10 m/s brakes to stop in 5 seconds.

Homework Statement Hey, if a 1000 kg car is moving at 10 m/s brakes to stop in 5 seconds. What would the avergae breaking force be? Homework Equations The Attempt at a Solution
32. ### A question about DC Motors, Clutches, and Brakes.

I am making a functional model friction crane. I am in the design and material gathering phase right now, but I have a question about DC Motors and how they would behave in a certain situation. I plan on having a DC motor spinning a shaft with a clutch on it. When the clutch is engaged...
33. ### Find torque in disc brakes given normal force and coefficient of friction

Homework Statement In the disc brakes that slow down a car, a pair of brake pads squeezes a spinning rotor; friction between the pads and the rotor provides the torque that slows down the car. If the normal force that each pad exerts on a rotor is 85 N, and the coefficient of friction is 0.62...
34. ### How do brakes bring a car to rest?

Homework Statement If only an external force can change the state of motion of a body, how can the internal force of the brakes bring a car to rest? The Attempt at a Solution I think that it may be because friction between brakes and wheels converts kinetic energy into heat. Or perhaps...
35. ### I remember my teacher saying that anti-lock brakes worked better

I remember my teacher saying that anti-lock brakes worked better because of the static friction coeffiecient was higher than the kinetic friction, but i never understood why. Is it beacuse when you stab the brakes their is a larger impulse?
36. ### How far does the car travel before its brakes are applied to slow down?

Two cars start from rest at a red stop light. When the light turns green, both cars accelerate forward. The blue car accelerates uniformly at a rate of 5 m/s2 for 4.3 seconds. It then continues at a constant speed for 9.7 seconds, before applying the brakes such that the car’s speed decreases...
37. ### Something's wrong with my brakes. Help?

'92 Chevy Lumina sedan 3.1L engine They're really soft. They work, but not like brakes in every other vehicle I've ever driven. When I push down, I have to pump a bit to get to a reasonable level of responsiveness. I can hear what sounds like air squeezing out as I pump. I've replaced...
38. ### Force exerted by aircraft dive brakes- where did I go wrong?

Homework Statement An aircraft of 5000kg mass is diving vertically downwards at a speed of 500 knots. The pilot operates the dive brakes at a height of 10 000m and reduces the speed to 325 knots at 7000m. If the average air resistance of the remainder of the aircraft during the deceleration...
39. ### Magnetic Fields & Metal: Exploring Currents & Brakes

let's say we have a square piece of metal and we put this piece in a variable magnetic field, would it get heated? is this the idea of a current? If we have a rotating metal disk (as the case of a saw for instance), and then we put this rotating disk in a constant uniform magnetic field such...
40. ### Speed of a truck wthout brakes down a hill

1. Hi, I'm trying to find the speed that a truck rolling down a hill which brakes have failed. The hill has a drop of 85 meters vertically and a horizontal of 1510 meters. The hill is like a right angle where the bottom right is the 90 degrees. The bottom left is 3.2 degrees and the top right...
41. ### Defining dimensions of a linear eddy current brakes permanent magnets

I am designing an eddy current brake system for use in roller coaster design. I have the flux density required to reduce the speed to what i want it to be. what i need to do from that is work out the dimensions needed to obtain his flux density. the configuration is for identical magnets...
42. ### Disk brakes along the rim of the wheel?

Disk brakes along the rim of the wheel?? Hi friends, I have a doubt. I heard that when we keep the disc brake along the rim of the wheel, less energy is required to stop the wheel. Why is it so?? Why is it not used in today's bikes?:confused:
43. ### Distance traveled if a driver hits the brakes

Homework Statement A person driving her car at 51 km/h approaches an intersection just as the traffic light turns yellow. She knows that the yellow light lasts only 2.0 s before turning to red, and she is 30 m away from the near side of the intersection (Fig. 2-29). The intersection is 15 m...
44. ### Brakes, static equilibrium problem is my Free Body Diagram correct?

Homework Statement Calculate minimal force P of the brakes during the stopping of the wheel. http://img823.imageshack.us/img823/6017/problemzy.jpg Solution is P=34.3 [N] Homework Equations (Written on scan above) The Attempt at a Solution...
45. ### Eddy Current Brakes: Explaining the Mechanics

Hey guys, our professor did a demo for us after the class since they just received new equipment, and unfortunately he didn't want to explain to us all the mechanics of what we witnessed because I'm currently following the mechanics course, but this was an E&M related demonstration. I know a...
46. ### Calculating Work Done by Brakes: A Step-by-Step Guide

Homework Statement the driver of a car mass 1368kg braked momentarily to slow down from 92km/h (25.556m/s) to 63 km/h (17.5m/s) how much work was done by the brakes (friction). Homework Equations w = Fd F=ma difference between initial acceleration and final acceleration s 8.056m/s...
47. ### After brakes are applied how far does the car travel? - integrating twice

Homework Statement t seconds after the brakes of a car are put on, the acceleration of the car is a(t) = -6t - 4 ft/sec^2. If the automobile was moving at the speed of 32 ft/sec when the brakes were put on, how far does it go before stopping? Homework Equations a(t) = -6t - 4 ft/sec^2...
48. ### A Level mechanics: Force exerted on a car by a trailer when brakes are applied

Hi :) I have an A Level Mechanics 2 exam in 3 days. I managed to 'solve' this problem from my book, but I'm having some trouble with the underlying concepts. It would be really nice if someone could explain part (c) of the question to me (I've included my solution below but I don't understand...
49. ### Which forces does work as a car brakes?

Homework Statement Which forces does work? http://www.screencast.com/users/ntrinh3/folders/Jing/media/3f09a85d-142c-4f73-a8a8-1ad506d5c2b8 Homework Equations W=fdcos(theta) The Attempt at a Solution I always thought normal and friction does no work because it is perpendicular to...
50. ### Understanding Antilock Brakes: A Primer

Whatever the outcome of the Prius brake recall, it sounds like educating the public on antilock brakes will be part of the answer. Wozniak is quoted as indicating the car would coast for a bit on an icy road, rather than stop immediately, and that this was "scary". It's "scary" if you...