dynamics lab 2

dynamics lab 2Braking system

Object: To determine limiting coefficient of frictionTheory:When motor is disengaged by switching off the power source of the magnetic clutch, wheel is independent of motor. If a weight W is applied at the lever arm end, this weight will cause a normal reaction N on the wheel due to lever arm, resulting in brake applied on the wheel. Now we keep adding the weights on the wheel at the specified place, till the wheel just starts to slip. This weight W multiplied by the wheel radius will give the applied torque, which is resisted by the friction torque due to brake. When the wheel just starts to rotate, we can then use the following equation:

Frictional Force = Coefficient of Friction x Normal reaction force

Ff = x NProcedure:1. First of all, the brake is applied to the stationary wheel, by hanging known weight W1 with lever arm, while motor disengaged by switching off the power supply of magnetic clutch.2. Hang the weight hanger at the specified point on the wheel3. Keep on adding the weights in small increments.4. Note the value of W when the wheel just begins to slip.

Observation and Calculations:

N = (b/a) WWhere a = 7 inch b = 14 inch W1 = Weight of Lever arm = 2kg W2 = weight hung on Lever arm W = Net weight applied for braking = W1 + W2N = 2WN = 2(W1 + W2)

Serial No.Net weight applied for brakingW (N)Weight Hung with wheel

W (N)N(N)

1. (2 + 0.5) x 9.8 = 24.5 5 x 9.8 = 49.049.01.00

2. (2 + 0.6) x 9.8 = 25.5 6 x 9.8 = 58.851.21.15

3. (2 + 0.7) x 9.8 = 26.56.5 x 9.8 = 63.753.01.20

The graph of W-N is a straight line passing through origin and has a gradient equal to the coefficient of friction i.e. = (W2 W1)/ (N2 N1) = 50/45 = 1.11Hence the limiting coefficient of friction is mathematically found to be equal to 1.11

Sources of Error:1. An uncalibrated gage meter which measures deflection or slipping could result in incorrect results.2. Slipping of the wheel occurs instantly and person has no idea when it is going to occur hence more weight can be added giving mislead results.