# Brake Rotor Heat: Calculating Temperature for 120kg Object at 30mph

• IM31408
In summary, the conversation is about designing a brake rotor for a bike and the need to know how much the rotor will heat up during braking. The person is seeking help in finding the necessary equations and material information to calculate the energy needed to heat up the rotor and to address heat dissipation. They also mention the possibility of using a computer program or conducting physical testing to determine the best design.
IM31408
This isn't so much a homework question but rather something I need to know in order to design something.
I need to know how much a brake rotor will heat up during braking. The force it needs to stop is a 120kg object traveling at 30 mph. I don't know any of the equations necessary to figure this out. I need to know this because I am designing a brake rotor for a bike and it cannot exceed a certain temperature. Any help would be great. Thanks.

E(kin) = ½*m*v*v

m=120kg
v=14m/s (30mph)

E(kin)=11760Jouel

You need to know which material you are using. For the given material you can find how much energy you need to heat one kilogram one degree celcius (or which ever scale you crazy americans use) ;-)

How would I deal with heat dissipation?

I would think you would have to know the exact airflow and turbulance around the break, the air temp. and the air hum. You would need a big computer progran such as SolidWorks to simulate it! With a price tag of around 10.000dollers fore a single user program, it might be a little much! I think Ferrie spends millions on these calculations and simulations.
I would propose testing it! The larger the surface arrea the better (drill a lot of holes) :-)

I can provide you with some basic equations and concepts to help you calculate the temperature of the brake rotor during braking. First, we need to understand the factors that affect the temperature of the brake rotor. These include the mass of the object being stopped, the initial velocity of the object, the friction between the brake pads and rotor, and the thermal properties of the materials involved.

To calculate the temperature of the brake rotor, we can use the equation for heat transfer, which is Q = mcΔT, where Q is the heat transferred, m is the mass, c is the specific heat capacity of the material, and ΔT is the change in temperature. In this case, the heat transferred is equal to the work done by the brake pads on the rotor, which can be calculated using the equation W = Fd, where W is the work, F is the force applied, and d is the distance over which the force is applied.

To determine the force applied by the brake pads, we can use the equation F = ma, where F is the force, m is the mass of the object, and a is the acceleration. In this case, the acceleration can be calculated using the equation a = (vf - vi)/t, where vf is the final velocity (zero in this case, as the object is being stopped), vi is the initial velocity (30 mph), and t is the time it takes for the object to come to a stop. This time can be calculated using the equation t = d/vi, where d is the distance over which the object is being stopped.

Once we have calculated the force applied by the brake pads, we can use the equation for work to determine the heat transferred to the brake rotor. This heat will cause the temperature of the brake rotor to increase by a certain amount, which can be calculated using the equation ΔT = Q/(mc). The specific heat capacity of the material can be found in reference tables or through experimentation.

It is important to note that this calculation is an approximation and may not account for all factors that may affect the temperature of the brake rotor. It is always best to test and monitor the temperature of the brake rotor during actual use to ensure it does not exceed the desired limit. I hope this information helps in your design process.

## 1. What factors affect the temperature of a brake rotor?

The temperature of a brake rotor is affected by several factors, including the speed of the object, the weight of the object, the material of the rotor, and the efficiency of the braking system.

## 2. How is the temperature of a brake rotor calculated for a 120kg object at 30mph?

The temperature of a brake rotor can be calculated using the formula Q = m * c * ΔT, where Q is the heat energy, m is the mass of the object, c is the specific heat of the material, and ΔT is the change in temperature. By plugging in the values for a 120kg object traveling at 30mph, the temperature can be calculated.

## 3. What is the specific heat of a brake rotor material?

The specific heat of a brake rotor material varies depending on the type of material used. Common materials for brake rotors include cast iron, ceramic, and carbon-ceramic, each with their own specific heat values. However, for general calculations, the specific heat of cast iron can be used, which is approximately 0.46 J/g·K.

## 4. Can the temperature of a brake rotor be too high?

Yes, the temperature of a brake rotor can become too high if it exceeds the melting point of the material or if it causes excessive wear on the rotor. This can be dangerous as it can lead to brake failure and loss of control of the vehicle.

## 5. How can the temperature of a brake rotor be reduced?

The temperature of a brake rotor can be reduced by improving the efficiency of the braking system, using materials with higher specific heat values, and increasing the surface area of the rotor to dissipate heat more effectively. Additionally, allowing for longer cooling periods between braking events can also help reduce the temperature of the rotor.

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