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- The materials required for this science project:A DC 24V, 500W power supply
- A DC 24V, 30W servomotor
- A DC 24V, 50W servomotor
- A DC 24V, 70W servomotor
- A DC 24V, 100W servomotor
- A multi meter
- An ammeter
- A stopwatch


1. For this science project, the independent variable is the rating of the DC motor used – 30 watt, 50 watt, 70 watt and 100 watt. The dependent variable is the energy lost due to friction in the DC motor. This is determined by measuring the voltage, current and time taken for the motor to stop after the power is turned off. The constants (control variables) are the size of the power supply and the type of DC motor used.

2. The experiment is done by selecting 4 different ratings of DC motors from the same series and manufacturer. This is to ensure that the construction of the DC motors  is the same and to eliminate the friction factor that may result from different types of construction. The suggested power rating for this experiment is 30 watt, 50 watt, 70 watt and 100 watt.

3. The DC motor is connected to the 500 watt DC power supply. It is allowed to turn freely without any load. The multi meter and ammeter are used to measure the input current and DC voltage at the motor input. The measurements are recorded in the table below.

4. The power supplied to the motor is calculated as below :

Power (W) = Input DC voltage (V) x Input DC current (A)

This power will be the work (Joule) required to be done by the internal friction of the motor, in order to bring the motor to a stop.

5. The power to the motor is switched off and the stopwatch started. The time needed for the motor to stop is recorded in the table given below.

6. The amount of friction power required to bring the motor to stop is calculated as :

Friction power (W) = work done to stop motor (Joule) / time to stop motor (seconds)

The results are recorded in the table given below.

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Complexity level:
Project cost ($):
Time required:
1 hour to prepare, 1 day for the science project experiment
Material availability:
Motors will have to be purchased from an appropriate hobby store
Safety concerns:

Handle all electrical devices and motors with care to prevent electric shock/injury from moving parts. The assistance and supervision of a suitably qualified adult is required.