Some fish have bladders full of gas inside their bodies. They can control the amount of gas inside these bladders. Explain how these bladders can be used by the fish to move up or down in the water.
Fish use their gas-filled bladders, also known as swim bladders, to maintain and control their buoyancy in the water. These bladders are flexible sacs located in their abdominal cavity, and they help the fish to move up and down in the water column without expending much energy.
When a fish wants to move upwards, it needs to decrease its overall density to become positively buoyant. To achieve this, the fish contracts special muscles located around the swim bladder, forcing the gas inside to compress. As the gas compresses, it takes up less space, reducing the bladder's overall volume. This decreased volume allows the fish's body to become denser than the water around it, causing it to rise towards the water's surface.
Conversely, when a fish wants to move downwards, it needs to increase its overall density to become negatively buoyant. The fish relaxes the muscles surrounding the swim bladder, allowing the gas inside to expand. As the gas expands, it takes up more space, increasing the volume of the bladder. This increased volume reduces the fish's overall density, making it less dense than the water around it and causing it to sink towards the bottom.
By adjusting the amount of gas in their swim bladders, fish can finely control their buoyancy and maintain their desired depth in the water column. This ability is crucial for activities such as foraging, avoiding predators, and conserving energy while swimming.
please shorten that
Fish control the amount of gas in their swim bladders to move up or down in the water. When they want to rise, they compress the gas, becoming more buoyant. When they want to sink, they let the gas expand, becoming less buoyant. This allows them to adjust their depth in the water without using much energy.
Explain why a body weighs less in water (which has a density of 1 g/mL) than it does in air.
A 500 g mass is weighed in air and then in water. This experiment is repeated with salt water (density of 1.2 g/mL) and methylated spirits (density of 0.8 g/mL). Compare the weight of the body in these liquids to the results for water. Explain the differences.
A body weighs less in water than it does in air due to buoyancy, which is caused by the upward force exerted by a fluid on a submerged object. When an object is placed in a fluid, it displaces some of that fluid. The displaced fluid exerts an upward force on the object, counteracting the force of gravity, and reducing the weight of the object.
In the given experiment, the weight of a 500 g mass is first measured in air. When it is weighed in water, the weight appears to decrease. This is because the body displaces some of the water, and the upward buoyant force exerted by the water reduces the apparent weight of the body. Since water has a density of 1 g/mL, the buoyant force acting on the body is equal to the weight of the water displaced.
When the experiment is repeated with saltwater, which has a higher density of 1.2 g/mL, the buoyant force exerted on the body will be greater compared to water. This means that the apparent weight of the body will be even lower in saltwater compared to water.
Conversely, when the body is weighed in methylated spirits, which has a lower density of 0.8 g/mL, the buoyant force exerted on the body will be lower compared to water. As a result, the apparent weight of the body will be higher in methylated spirits compared to water.
These differences in weight measurements in different liquids are because the buoyant force depends on the density of the liquid. The higher the density of the liquid, the greater the buoyant force, and the lower the apparent weight of the body. Conversely, lower liquid density results in a lower buoyant force and a higher apparent weight.