Mecânica e máquinas simples · GCSE Physics Forces & Machines
Simulador de cadernal e roldanas
Simulador de sistema de roldanas e cadernal: vantagem mecânica e rendimento
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- Sem cadastro
- Dedução ao vivo
- Modo projetor
- Folha de exercícios A4
Janela de simulação 3D● 60 FPS
Variáveis de controle do experimento
N
N
m
N
Deduções e métricas em tempo real
Força motriz F
--
Percurso da corda s
--
Rendimento mecânico η
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Trabalho total W_total
--
Dedução de fórmulas em tempo real
Fórmula fundamental:
--Substituição de valores:
--Estado físico: --
Ferramenta relacionada:
⚙️ Standard Tool: V-Belt Pulley Calculator ↗
Exemplos clássicos e armadilhas de exame
Worked Problem
Problema: A block and tackle with n=3 lifts 400N. Movable pulley weighs 50N, friction negligible. Find effort F and efficiency η.
Derivação passo a passo:
- Effort F = (G + G_mov)/n = (400 + 50)/3 = 150N; efficiency η = G / (n*F) = 400 / (3*150) ≈ 88.9%.
Worked Problem
Problema: A pulley lifts 600N by 3m with effort 250N moving 9m. Find useful work, total work, and efficiency.
Derivação passo a passo:
- W_useful = 600*3 = 1800J; W_total = 250*9 = 2250J; η = 1800 / 2250 = 80%. Here n = s/h = 3.
Folha de investigação em aula e exercícios
Q1. Variant 1: An operator on the ground pulls downward to lift 500N with G_mov=60N. What is the minimum n and effort?
Answer Key: Pulling downward requires rope from fixed pulley (n=2). Effort F = (500+60)/2 = 280N.
Q2. Variant 2: Does the same pulley have identical efficiency lifting 200N vs 600N?
Answer Key: No, efficiency is higher with 600N because useful work G*h forms a larger fraction of total work.
Q3. Variant 3: A pulley with η=75% lifts a load at 0.2m/s with power 40W. Find the load weight G.
Answer Key: Useful power P_useful = 0.75*40W = 30W. Since P_useful = G*v, G = 30 / 0.2 = 150N.
Perguntas frequentes e erros comuns
What is the "odd movable, even fixed" rigging rule?
If the number of load-bearing strands n is odd (3, 5), the fixed end of the rope must be anchored to the movable block. If even (2, 4), anchor to the fixed block.
Does pulling downward from the ground change mechanical advantage?
Yes. The final rope segment coming off the fixed pulley changes direction rather than supporting the load, yielding n=2 strands from two pulleys.
Can a pulley system save work or energy?
No. By the law of conservation of energy, no machine saves work. Effort is reduced by factor n (F=G/n), but distance increases by factor n (s=nh). Total work always exceeds useful work due to friction and pulley weight.
How do you maximize pulley efficiency?
1) Minimize movable pulley weight; 2) lubricate bearings to reduce friction; 3) operate near rated capacity so useful work dominates total work.