Newton's 1st Law
Sir Isaac Newton's first law of motion states that an object in motion will continue in that motion forever until acted upon by an outside force. A perfect example of this principle being ignored in Infinity War comes right at the beginning of the film. When Thanos destroys the ship with all the Asgardians on board there is quite a large explosion. With an explosion of that magnitude debris (like Thor who was inside the ship when it exploded) would be hurled away from the spot of the explosion at a non zero velocity. When the Guardians find Thor though, he is just floating around where the ship was with no real noticeable velocity. By looking at the motion of objects in the background and comparing it to Thor it seems that the perceived motion of Thor is coming from the motion of the Guardian's ship, and not from Thor. In reality, the debris that was flung into space, like Thor, should be a ways away from the spot of the explosion because it would not have any outside forces stopping its motion so it should travel in a straight line away from the wreck at the speed the explosion set it at.
Newton's 2nd Law
Newton's second law of motion states that if there is an acceleration of on object with mass, then there must be a force applied to it to cause the acceleration. The biggest disregard for this law in the film is how Ebony Maw and Doctor Strange just levitate in the air without any sort of thrust upward. For them to float they would need to supply a force greater than and in the opposite direction to their gravitation force to lift themselves off the ground and then a force equal to their weight while in the air. Neither of these magicians supply any sort of visible force to allow them to float in mid-air but the movie just looks past that and allows them to do it anyway.
Newton's 3rd Law
Newton's third law of motion states that every force exerts a force with equal magnitude but in the opposite direction to the original force. One moment where this seemed to be ignored in Infinity War is when Thanos pulls one of Titan's moons and throws it at Iron Man. While the movie shows Thanos pulling and exerting a force to pull the moon downward, there is not indication of Thanos having an equal and opposite force acting against him. If there was an equal and opposite force, he would either be flung from the surface of Titan or if he was anchored enough, Titan would shift toward the moon.