“Mass Pulley Experiment”

Force and Energy, Velocity and Acceleration, and power 

In this lab experiment we used the Lego Windstorm motor to lift weights with a pulley. We used this, to explore Newton’s 2nd Law, the law of conservation of energy, velocity and acceleration and power.

The point of the experiment is to find the speed, acceleration, time and the amount of battery discharge that the robot uses.

By setting the power level of the motor, this will set the toque on the motor wheel which will result in a particular force used to lift the masses.  The higher the power level, the greater the force will be.

To find this data we use two methods, by doing it a few times with the power level fixed but changing the mass and by changing the power and then keeping the mass constant.

1.

Exploring Newtons’s 2nd law, F=ma, BY KEEPING THE power level fixed and changing the mass. We ran it 3 times.

In this case the power level is stated in %, so it was fixed at 75%.

And yes the acceleration varies with the power level. We can see in the graph bellow because if the power level decreases the mass increases.

Power level %         Mass (kg) 

75                                    0.25

75                                   0.18

75                                   0.12

75                                   0.07

Then, we keep the mass the same and change the power level.Mass (kg)

Mass (kg)      Power level %

0.07                    60

0.07                    45

0.07                    30

0.07                    20

And these are the results for acceleration that we get for each trial and they certainly change.

Acceleration vs Force, here I show how we use a different power level % and also get a different acceleration (RPM/s)

Power level %                Acceleration RPM/s) 

75                                            46.96716

60                                             29.09715

45                                             16.62116

30                                             6.525699

20                                             2.437297

2.  We now will explore the Law of Conservation of energy by  computing:

,  with h as the height that the center of mass of the weights travel.

With the power level fixed, study how the battery energy drainage changes as a function of mass.  Since the energy of the battery is converted to the potential energy of the masses, you would expect that the greater the masses, the greater is the battery drainage.  However, the battery level reading is not that accurate, so you should repeat your measurements several times and look at the average battery drainage as a function of mass.

These are the results in the scatter graph bellow.

3. Now we calculate the average power used by the motor which equals:

,

Power Level %          Power= mgh/t (W)

75                                        0.09292694760

60                                         0.07127272730

45                                          0.055675362

30                                          0.034885579

20                                          0.021346966

The graph bellow shows the results. We also added a linear trend line with an equating and R2, the curve is exactly linear.