 # Physics in LEGO Mindstorms: Energy Accumulation and Conservation. Part 4 - experiment for energy in Joules ProPreview

We dispay the speed of rotation of the wheels on the brick screen. We use the math blocks to do a proper calculations from rotation to radians per second. Knowing the speed, the radiuses and the mass of the wheels we find energy in Joules accumulated in the construction.

• #117
• 29 Nov 2015
• 10:35

### English

We did number of calculations and we went through the theoretical part of conserving energy into the construction that we built. Last we built an EV3 program that was showing on the display the speed of rotation of our motor. If I now start the program

what you can see is that the speed of rotation of our motor is about 960 degrees. Previously it was 800 but I suppose that the battery was not that charged and now because of the battery we can see that it is rotating faster. This is the speed of rotation of our motor in degrees per second . so it's about 960 degrees per second. Because we did a calculation we need actually the speed of rotation

in radians per second. Now I'll show you how to improve the program so that you can show the speed of rotation in radians per second.

This here is the program developed previously. It was a motor, we reset the rotation sensor, we start with the large motor, we waited for a second and we measure the number of degrees that it rotated and we displayed this value on the display of the brick.

and we are doing this in a loop for 20 times, so actually 20 seconds and this will show the speed of rotation for 1 second, the speed of rotation in degrees, the angular velocity. But we want to show this in radians per second. How can we do this? We must convert this value of degrees to radians. We'll take 1 mathematical block

and we can choose advanced and in the advanced tab we need the following.

These are the degrees per second, so we must delete these degrees per second on 360. So we divide,

a is divided by 360 degrees and the result from this is multiplied by 2 pi and pi is 3,14. So that's the formula for converting degrees per second to radians per second.

We take the result and we display it on our brick.

This here is the brick, let's start the program, we start the program, it starts rotating and the result is actually the radians per second. It's about 16,7 radians per second, that's the speed of rotation of our motor. Now I'll stop this and let's try to connect this motor to our construction. In our construction we have 3 wheels. We have the first, the second and the third wheels. Let's try to rotate them with the motor.

We have here the axle for rotation. What will happen now is that the motor will input some power to the system. Because of the motor the wheels will start rotating and they'll start rotating faster and faster and more energy will be accumulated. Let's transfer the brick right here so that you can also see it and I'll now start the program.

You can see that the construction is rotating faster and faster.

The maximum speed that we reach is about 8 radians per second. So when we have the 3 wheels and we are trying to rotate these 3 wheels with the motor. The maximum speed that we reached was about 8 radians and this is the speed of the whole system. The motor is inputting a speed with 8 radians and we can calculate 8 by 25 it's about 200 radians per second, the speed of rotating of the 3 wheels. The conclusion here is that this motor has a finite power.