Is the way the force is produced i.e. thrust instead of buoyancy the difference?
I need to introduce a little bit of theory which takes you beyond the content of Higher Physics – the new bit is in bold below. When an object is immersed or partially immersed in a fluid then the object displaces the fluid – you can see this for a boat floating on water – the upthrust is equal to the weight of fluid displaced. A good example of this principle when upthrust and weight are equal is the Falkirk Wheel – the weight of a gondola is the same whether or not there is a barge in the gondola – the barge floats because vertical forces balance – the weight of the barge is balanced by the buoyancy force – the additional bit of theory indicates that the weight of the floating barge is equal to the weight of the water it has displaced from the gondola. Take the barge out of the gondola and it is replaced by an equal weight of water. Similarly, if the weight of the balloon is equal to the buoyancy force, the presence of the balloon has no effect on the weight of the box and its conten
