Discussion
From this experiment, it can be determined that the value of the coefficient of friction between the wire and the belt is 0.2782 (which is dimensionless). In addition, T1 becomes smaller (so the belt tension ratio becomes greater) when the angle of contact is increased, which can be explained by considering equation 2, as T2 cannot change for a given stationary mass. Comparing the experimental results to the theoretical predictions (made from the calculated value of μ, there is a relatively good agreement, especially when neglecting the πc result. The slightly higher gradient of the experimental results is likely due to an error (systematic) in the calibration of the load cell, causing it to become more inaccurate at higher tensions. …show more content…
The main reason for this power loss is likely due to the slipping of the belt with respect to the driven pulley. This is because the two surfaces of the wire and pulley are not physically attached, but rather the transmission of force relies on the friction between the two surfaces. Therefore, under this scenario it can be considered that the wire was not effectively in contact with the pulley the whole time (it ‘slipped’) and so some power was wasted. This problem is largely reduced by using a toothed (or timing) belt as opposed to a flat belt (see figure 2), as they have teeth on the inner surface effectively locking the belt in place relative to a segment of the pulley (also toothed). Other reasons for the discrepancy include inaccurate readings on the power pack, resistance in wiring, friction in the bearing of the motor (and general internal friction) as well as losses from the pulley as …show more content…
At low loads the reason for the lack of efficiency is down to the extent of the slipping as the tensions are less, however the reason for the decreasing efficiency at high torques is down to losses in the engine itself. With engines, the term ‘stall torque’ refers to when the torque is great enough that the output rotational speed becomes zero, as the mechanical resistance increases to the extent that more current cannot be consumed from the supply. This will be the greatest possible torque as there will be no slip, but the rotational power will be zero as the body is not moving. In this scenario, the motor effectively simply functions as a large resistor, and so is very prone to overheating as almost all the power is dissipated as heat inside the motor. Conversely, the minimum torque occurs when there’s no load to pull, and this is usually called the ‘free rpm’. As , the maximum power possible (and so maximum efficiency possible) occurs exactly in the middle of zero and peak torque (and so in the middle of zero and maximum angular velocity). In addition, it must be considered that electric motors themselves are not 100% efficient, due to effects such as internal resistance and internal friction, so there is some simplification in using the power outputted by the power supply rather than a reading from
From this experiment, it can be determined that the value of the coefficient of friction between the wire and the belt is 0.2782 (which is dimensionless). In addition, T1 becomes smaller (so the belt tension ratio becomes greater) when the angle of contact is increased, which can be explained by considering equation 2, as T2 cannot change for a given stationary mass. Comparing the experimental results to the theoretical predictions (made from the calculated value of μ, there is a relatively good agreement, especially when neglecting the πc result. The slightly higher gradient of the experimental results is likely due to an error (systematic) in the calibration of the load cell, causing it to become more inaccurate at higher tensions. …show more content…
The main reason for this power loss is likely due to the slipping of the belt with respect to the driven pulley. This is because the two surfaces of the wire and pulley are not physically attached, but rather the transmission of force relies on the friction between the two surfaces. Therefore, under this scenario it can be considered that the wire was not effectively in contact with the pulley the whole time (it ‘slipped’) and so some power was wasted. This problem is largely reduced by using a toothed (or timing) belt as opposed to a flat belt (see figure 2), as they have teeth on the inner surface effectively locking the belt in place relative to a segment of the pulley (also toothed). Other reasons for the discrepancy include inaccurate readings on the power pack, resistance in wiring, friction in the bearing of the motor (and general internal friction) as well as losses from the pulley as …show more content…
At low loads the reason for the lack of efficiency is down to the extent of the slipping as the tensions are less, however the reason for the decreasing efficiency at high torques is down to losses in the engine itself. With engines, the term ‘stall torque’ refers to when the torque is great enough that the output rotational speed becomes zero, as the mechanical resistance increases to the extent that more current cannot be consumed from the supply. This will be the greatest possible torque as there will be no slip, but the rotational power will be zero as the body is not moving. In this scenario, the motor effectively simply functions as a large resistor, and so is very prone to overheating as almost all the power is dissipated as heat inside the motor. Conversely, the minimum torque occurs when there’s no load to pull, and this is usually called the ‘free rpm’. As , the maximum power possible (and so maximum efficiency possible) occurs exactly in the middle of zero and peak torque (and so in the middle of zero and maximum angular velocity). In addition, it must be considered that electric motors themselves are not 100% efficient, due to effects such as internal resistance and internal friction, so there is some simplification in using the power outputted by the power supply rather than a reading from