Question

Now, consider a beaker of water placed on a scale. your object (the combined body) is then suspended in the water. comment on each of the following student predictions regarding what happens to the reading of the scale. with which do you agree or disagree?

1. we predict the reading of the scale will not change because the object is suspended in the water and never touches the bottom of the beaker.
2. we predict the reading of the scale will increase by an amount equal to the object's weight because water is incompressible so we are effectively weighing the object and the beaker together.
3. we predict the reading of the scale will decrease by an amount equal to the tension force suspending the object.

Answer 1

The scale's reading will increase by the object's weight due to Archimedes' principle, with the buoyant force equaling the weight of the displaced fluid, despite the object not touching the bottom of the beaker.

Step-by-step explanation:

When an object is suspended in water, its presence still exerts a force on the surrounding fluid, and, by extension, on the beaker and the scale below. The reading of the scale will change due to Archimedes' principle, which states that the buoyant force on a submerged object is equal to the weight of the fluid it displaces. Therefore, the second prediction is more accurate: the scale will increase by an amount equal to the object's weight, indicating not just the water's weight but also the apparent weight of the object.

This is because even though the object does not touch the bottom, it displaces a volume of water whose weight must be supported by the beaker and, in turn, by the scale. This displaced water's weight adds to the total weight measured by the scale. The first and third predictions fail to consider this displacement effect and are thus incorrect.