Braking Energy
Calculate the energy dissipated in braking, E = ½·m·(v₁² − v₂²), from the mass m (kg), the initial velocity v₁ and the final velocity v₂ (m/s). When a vehicle or machine brakes, its KINETIC energy is converted — by brake friction — into HEAT. The dissipated energy is the kinetic-energy change: braking to a stop (v₂ = 0) dissipates all the initial kinetic energy; partial braking, the difference. This heat must be ABSORBED and DISSIPATED by the brake without overheating beyond the limit (above which the friction material loses effectiveness — fading — and may even burn or glaze). That is why brakes for heavy vehicles, long descents (mountain trucks) and severe duty need large thermal capacity (big, vented discs, or auxiliary brakes like engine braking and retarders, dissipating energy by other means without overloading the service brakes). Braking energy grows with the SQUARE of velocity: braking from 100 km/h dissipates FOUR times more energy than from 50 km/h — so high-speed braking is so much more demanding. This is the basis of brake thermal design and overheating checks in repeated or prolonged braking. Enter the mass and the initial and final velocities.
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Energia de frenagem
A energia dissipada em uma frenagem é E = ½·m·(v₁² − v₂²), a partir da massa m, da velocidade inicial v₁ e da velocidade final v₂. Quando um veículo ou máquina freia, sua energia cinética é convertida — pelo atrito do freio — em calor. A energia dissipada é a variação da energia cinética: se freia até parar (v₂ = 0), é toda a energia cinética inicial; se freia parcialmente, é a diferença. Esse calor precisa ser absorvido e dissipado pelo freio sem que ele superaqueça além do limite (acima do qual o material de atrito perde eficiência — o fading — e pode até pegar fogo ou vitrificar). É por isso que freios de veículos pesados, de descidas longas (caminhões em serra) e de aplicações severas precisam de grande capacidade térmica (discos grandes, ventilados, ou freios auxiliares como o motor-freio e o retarder, que dissipam a energia por outros meios). A energia de frenagem cresce com o quadrado da velocidade: frear de 100 km/h dissipa quatro vezes mais energia que de 50 km/h — por isso frenagens em alta velocidade são tão mais exigentes. Este cálculo é a base do dimensionamento térmico de freios e da verificação de superaquecimento em frenagens repetidas ou prolongadas. Informe a massa e as velocidades inicial e final.
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Brake Temperature Rise
Estimate a brake's temperature rise from one braking, ΔT = E ÷ (m·c), from the braking dissipated energy E (J), the mass of the heat-absorbing component m (kg, the disc or drum) and the material specific heat c (J/(kg·°C), ~460 for steel, ~900 for aluminum). When a brake dissipates a braking's kinetic energy (converting it to heat), this heat is initially ABSORBED by the disc or drum mass, raising its temperature. This formula estimates that rise assuming ALL the heat goes into the component mass, with no loss to the environment (a conservative assumption, valid for a quick, isolated braking — in prolonged braking, part of the heat is dissipated by convection and radiation simultaneously). The temperature rise is critical because friction materials have a thermal limit: above a certain temperature (300-500°C for organic materials, more for metallic/ceramic), friction drops sharply (the FADING phenomenon, which has caused many mountain-descent accidents), the material degrades, and the disc can warp or crack from thermal shock. So severe-duty brakes use large discs (more mass, more heat-absorbing capacity), vented (more dissipation) and high-melting-point materials. This calculation is the heart of brake THERMAL design. Enter the dissipated energy, the mass and the specific heat.
Brake Power Dissipated
Calculate the power dissipated by a brake under torque, P = T·(2π·n/60), from the braking torque T (N·m) and the rotation n (rpm). Dissipated power is the rate at which the brake converts mechanical energy to heat — the product of braking torque and angular velocity. It differs from total braking ENERGY: energy is the total heat generated (joules), while power is the INTENSITY of that heat generation (watts), and it determines the brake's steady-state temperature. A brake dissipating much energy but slowly (low power) heats little; one dissipating the same energy fast (high power) heats much more. Dissipated power is critical in brakes working CONTINUOUSLY or repetitively: retention brakes on long descents, industrial equipment brakes (hoists, cranes, conveyors holding load), and dynamometers (which measure engine power precisely by dissipating it in a brake). There, the steady-state dissipated power sets the COOLING capacity needed (ventilation, water cooling) to keep temperature stable. Equating dissipated power to cooling capacity gives the equilibrium temperature. Enter the braking torque and the rotation.
Kinetic Energy Calculator
Compute kinetic energy KE = ½ m v² from mass (kg) and velocity (m/s). Result in joules.
The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.