In this free practice you will find a system of masses hanging by a thread, attached to a mobile at the other end. In this laboratory, you will be able to modify the masses, both of the mobile and of the weight suspended in the air, and the force of gravity for each environment (the Moon, Earth and Mars), among other parameters. The objective of this practice is to apply Newton's second law and determine the mass ratio, to achieve a desired acceleration in the motion of the body.