Buoyancy Reading Guide Page 114 - 115 Name:______
Grade 8 Science
Use pages 114 – 115 in your textbook to answer the following questions. Please use complete sentences unless you are filling in a blank.
1. Complete using notes from Bill Nye ideo: The buoyant force on an object immersed in a fluid is equal to the __ weight of the displaced fluid ______
2. Why do fish need swim bladders?
They use it to change their buoyancy so they can change depth.
3. What does the fish use to fill the swim bladder?
They fill it with gas from inside their bodies or air that they gulp.
4. (Think!) What happens to the volume of the fish’s body when the bladder is expanded?
The fish’s body expands in volume.
5. (Think!) Why does a change in volume change the buoyant force on the object?
When the object’s volume increases, it displaces MORE water, which increases the buoyant force’
6. What is needed for a relaxed swimmer to have positive buoyancy?
A relaxed swimmer needs to have lungs filled with air to float easily. (increases the volume of the body)
7. (Think) Explain why a wet suit increases buoyancy.
It increases your volume, but it has a low density, so it doesn’t increase your weight much – it gives you more buoyancy.
8. What is ballast?
Ballast is any material carried on ships, submarines, hot air balloons or dirigible that acts as a weight and changes buoyancy.
9. Why do empty ships need to use water for ballast?
The ballast helps the ship stay stable and to travel at the appropriate level in the water.
10. What are two ways that a hot air balloon can increase its buoyancy?
A hot air balloon can increase the volume of the gas inside by heating it (particles move farther apart with more heat!)
or
it can release some ballast to reduce its weight.
11. Why does heating the air increase buoyancy?
When the volume of the gas increases, the balloon displaces more of the fluid around it, so it has more buoyancy.
12. (Think!) Would a ship on the Great Lakes need more or less ballast than a ship on the ocean? Explain why.
A ship will float higher in salt water than in fresh water, because the displaced salt water will have more weight, so a ship on the ocean needs more ballast.