In the first picture, the weight pulls down with 1kg of force, and the ceiling pulls up with 1kg of force. If it didn't, there would be an imbalance, causing a

In the first picture, the weight pulls down with 1kg of force, and the ceiling pulls up with 1kg of force. If it didn't, there would be an imbalance, causing a net acceleration downwards. In the second picture, the first weight pulls rightward with 1kg of force, and the second weight pulls leftward with 1kg of force. The situation is exactly the same as the first, except with gravity providing the second force rather than the inter-molecular bonds responsible for maintaining the rigidity of the ceiling.